Cytochrome P450db; K+ channel

Quinidine HydroHClone monohydrate has an IC50 of 19.9±1.41 μM and a Hill slope of 1.15±0.15 (n=7), indicating that it inhibits WT mSlo3 (KCa5.1) channels. Similarly, quinidine hydrochloride monohydrate has a stronger inhibitory potency against F304Y mSlo3 (IC50 = 2.42±0.60 μM, n = 9, P<0.005; Hill slope = 0.98±0.12), but a lower inhibitory potency (IC50 = 38.4±6.77 μM, n = 5, P<0.001; Hill slope = 1.05±0.16) against R196Q mSlo3. There is a time dependence detected in the inhibition of F304Y mSlo3 by quinidine hydrochloride monohydrate [1].

When comparing baseline to other time points or comparison experiments, the direct application of quinidine hydrochloride monohydrate to the sciatic nerve produced dose-related decreases in the amplitudes of the descending compound muscle action potential (CMAP) and ascending somatosensory evoked potential (SSEP). Left versus right contralateral limbs treated with glucose. When quinidine hydrochloride monohydrate was applied, the latency of the SSEP and CMAP potentials increased in comparison to the baseline and contralateral side [2].

Mouse (m) Slo3 (KCa 5.1) channels or mutant forms were expressed in Xenopus oocytes and currents recorded with 2-electrode voltage-clamp. Gain-of-function mSlo3 mutations were used to explore the state-dependence of the inhibition. The interaction between quinidine and mSlo3 channels was modelled by in silico docking.
Key results: Several drugs known to block KSper also affected mSlo3 channels with similar levels of inhibition. The inhibition induced by extracellular barium was prevented by increasing the extracellular potassium concentration. R196Q and F304Y mutations in the mSlo3 voltage sensor and pore, respectively, both increased channel activity. The F304Y mutation did not alter the effects of barium, but increased the potency of inhibition by both quinine and quinidine approximately 10-fold; this effect was not observed with the R196Q mutation. Conclusions and implications: Block of mSlo3 channels by quinine, quinidine and barium is not state-dependent. Barium inhibits mSlo3 outside the cell by interacting with the selectivity filter, whereas quinine and quinidine act from the inside, by binding in a hydrophobic pocket formed by the S6 segment of each subunit. Furthermore, we propose that the Slo3 channel activation gate lies deep within the pore between F304 in the S6 segment and the selectivity filter.[1]

Twenty-seven rats were treated with 1, 3, and 5 μmol quinidine in 0.1 ml 5 % glucose. The mixed-nerve somato-sensory evoked potential (M-SSEP), dermatomal-SSEP (D-SSEP), and compound muscle action potentials (CMAP) were evoked and recorded. After positioning Gelfoam strips saturated with quinidine and 5 % glucose around the left and right sciatic nerves, potentials were measured at baseline, immediately after treatment, every 15 min for the 1st hour, and every 30 min for the next 3 h. After 2 weeks, the walking behaviors and potentials were again analyzed and myelinated fibers in the sciatic nerve were counted. Results: Quinidine applied directly to sciatic nerves reduced the amplitude and prolonged the latency in SSEPs and CMAP, compared to baseline and the contralateral right limbs (controls). This persisted for at least 4 h. After 2 weeks, electrophysiological tests and walking behavior showed no significant difference between the controls and experimental limbs. There was also no difference in the number of myelinated fibers in the sciatic nerves. Conclusions: Quinidine decreases amplitude and prolongs latency in the sciatic nerve in a dose-related manner without local neural toxicity.[2]

Absorption
The absolute bioavailability of quinidine sulfate is approximately 70%, but it ranges from 45% to 100%. The less-than-complete quinidine sulfate bioavailability is a result of first-pass metabolism in the liver. In contrast, the absolute bioavailability of quinidine gluconate ranges from 70% to 80%, and relative to quinidine sulfate, quinidine from quinidine gluconate has a bioavailability of 1.03. The tmax of quinidine sulfate extended-release tablets is approximately 6 h, while the tmax of quinidine gluconate goes from 3 to 5 h. The peak serum concentration reached with immediate-release quinidine sulfate is delayed for about an hour when taken with food. Furthermore, the ingestion of grapefruit juice may decrease the rate of absorption of quinidine.

Route of Elimination
The elimination of quinidine is achieved by the renal excretion of the unchanged drug (15 to 40% of total clearance) and its hepatic biotransformation to a variety of metabolites (60 to 85% of total clearance). When urine has a pH lower than 7, 20% of administered quinidine appears in urine unchanged. However, this proportion decreases to as little as 5% as it becomes more alkaline. The renal clearance of quinidine involves both glomerular filtration and active tubular secretion, moderated by pH-dependent tubular reabsorption.

Volume of Distribution
Quinidine has a volume of distribution of 2-3 L/kg in healthy young adults, 0.5 L/kg in patients with congestive heart failure, and 3-5 L/kg in patients with liver cirrhosis.

Clearance
The clearance of quinidine ranges from 3 to 5 mL/min/kg in adults. In pediatric patients, quinidine clearance may be two or three times as rapid.

The volume of distribution of quinidine is 2 to 3 L/kg in healthy young adults, but this may be reduced to as little as 0.5 L/kg in patients with congestive heart failure, or increased to 3 or 5 L/kg in patients with cirrhosis of the liver. At concentrations of 2 to 5 mg/L (6.5 to 16.2 umol/L), the fraction of quinidine bound to plasma proteins (mainly to (alpha)1-acid glycoprotein and to albumin) is 80 to 88% in adults and older children, but it is lower in pregnant women, and in infants and neonates it may be as low as 50 to 70%. Because (alpha)1-glycoprotein levels are increased in response to stress, serum levels of total quinidine may be greatly increased in settings such as acute myocardial infarction, even though the serum content of unbound (active) drug may remain normal. Protein binding is also increased in chronic renal failure, but binding abruptly descends toward or below normal when heparin is administered for hemodialysis.

...Essentially completely absorbed after oral admin; max effects occur within 1-3 hr, and persist for 6-8 more hr. Large fluctuations in plasma concentration... if repeated doses are given at this interval. ...IM admin... gluconate yields peak effects in 30-90 min.

...All administered compound is excreted by kidney, and about 10-50% appears in urine as unchanged quinidine, within 24 hr.

The bioavailability of quinidine is 70 to 80% after oral use but varies between individuals and preparations. The sulfate salt is rapidly absorbed in 60 to 90 minutes. Polygalacturonate salts produce peak quinidine concentrations in 5 to 6 hours; gastrointestinal absorption of gluconate salts is intermediate (peak 3-4 hours).

View More

ABOUT 90% OF QUINIDINE IN PLASMA IS BOUND TO PLASMA PROTEINS (ALPHA/ACID GLYCOPROTEIN AND ALBUMIN) THE DRUG ENTERS ERYTHROCYTES & ... BINDS TO HEMOGLOBIN; AT STEADY STATE, CONCN OF QUINIDINE IN PLASMA & ERYTHROCYTES ARE APPROXIMATELY EQUAL. QUINIDINE ACCUMULATES RAPIDLY IN MOST TISSUES EXCEPT BRAIN, & ... VOL OF DISTRIBUTION IS 2-3 L/KG. /QUINIDINE/

METABOLITES AND SOME OF THE PARENT DRUG (20%) ARE EXCRETED IN URINE; ELIMINATION HALF-TIME IS ABOUT 6 HR. /QUINIDINE/

LIVER METABOLISM & RENAL EXCRETION ARE THE MAIN ROUTES OF ELIMINATION. ENTEROHEPATIC CIRCULATION WOULD NOT SIGNIFICANTLY ALTER ABSORPTION KINETICS AS REFLECTED BY BLOOD CONCENTRATION. PMID:7264866

PEAK PLASMA CONCN OF 0.29 UG/ML OF QUINIDINE WERE MEASURED @ 4 HR AFTER ADMIN OF SUSTAINED RELEASE CAPSULE (250 MG QUINIDINE BISULFATE) AND DECLINED STEADILY DURING THE NEXT 8 HR, WHILE AFTER ADMIN OF SUSTAINED RELEASE TABLET (300 MG QUINIDINE SULFATE) THEY WERE FAIRLY EVEN DURING 2-10 HR AFTER DOSING. PLASMA CONCENTRATIONS WERE HIGHER AT LATER TIMES FOR THE CAPSULE THAN FOR THE TABLET. THE BIOAVAILABILITY OF QUINIDINE FROM THE CAPSULES DURING 12 HR WAS 184% COMPARED TO THE TABLET. MEAN QUINIDINE PLASMA CONCN WERE SIGNIFICANTLY GREATER @ 3, 4, 6, 8, & 10 HR AFTER ADMIN OF THE CAPSULE THAN AFTER THE TABLET.

For more Absorption, Distribution and Excretion (Complete) data for QUINIDINE SULFATE (24 total), please visit the HSDB record page.

---

Metabolism / Metabolites
Quinidine is mainly metabolized in the liver by cytochrome P450 enzymes, specifically CYP3A4. The major metabolite of quinidine is 3-hydroxy-quinidine, which has a volume of distribution larger than quinidine and an elimination half-life of about 12 hours. Non-clinical and clinical studies suggest that 3-hydroxy-quinidine has approximately half the antiarrhythmic activity of quinidine; therefore, this metabolite is partly responsible for the effects detected with the chronic use of quinidine.

Lactate conjugates of quinidine and its 3-hydroxy metabolite were detected in overdose suicide patient.

Quinidine is metabolized in the liver, principally via hydroxylation to 3-hydroxyquinidine and 2-quinidinone. Some metabolites have antiarrhythmic activity. Approximately 10-50% of a dose is excreted in urine (probably by glomerular filtration) as unchanged drug within 24 hr.

Quinidine metabolites include 3-hydroxyquinidine N-oxide, 2'-oxoquinidinone, desmethylquinidine, and quinidine N-oxide. While metabolism is highly variable between individuals, at least in cases of quinidine-induced torsade de pointes, the metabolites do not appear to contribute to the formation of dysrhythmias.

Quinidine undergoes extensive hepatic oxidative metabolism... One metabolite, 3-hydroxyquinidine, is nearly as potent as quinidine in blocking cardiac sodium channels or prolonging action potentials.

Most quindiidne is eliminated hepatically via the action of cytochrome P450 IIIA.

QUINIDINE YIELDS 2'-HYDROXYQUINIDINE AS METABOLITE IN MAN. /QUINIDINE; FROM TABLE/

MOST URINARY METABOLITES ARE HYDROXYLATED AT ONLY ONE SITE, EITHER ON THE QUINOLINE RING OR ON THE QUINUCLIDINE RING; SMALL AMOUNTS OF DIHYDROXY COMPOUNDS ARE ALSO FOUND. THE FRACTION OF A DOSE OF QUINIDINE THAT IS METABOLIZED & THE METABOLIC PATHWAY APPEAR TO VARY CONSIDERABLY FROM PATIENT TO PATIENT.

Quinidine is metabolized in the liver, principally via hydroxylation to 3-hydroxyquinidine and 2-quinidinone. The metabolites may be pharmacologically active. Approximately 10-50% of a dose is excreted in urine (probably by glomerular filtration) as unchanged drug within 24 hr. /Quinidine/

Quinidine has known human metabolites that include Quinidine-N-oxide and 3-Hydroxyquinidine.

---

Biological Half-Life
The elimination half-life of quinidine is 6-8 hours in adults and 3-4 hours in pediatric patients.

Quinidine generally has a plasma half-life of 6-8 hr in healthy inividuals, but half-life may range from 3-16 hr or longer. In one study in patients with Plasmodium falciparum malaria, the elimination half-life of the drug averaged 12.8 hr (range: 6.6-24.8 hr).

The usual plasma half-life of approximately 7 hours after intravenous administration is increased in the presence of chronic liver disease.

THE ELIMINATION HALF-LIFE OF QUINIDINE RANGES FROM 4 TO 10 HR IN HEALTHY PERSONS, WITH USUAL MEAN VALUE OF 6 TO 7 HR. HALF-LIFE IS SIGNIFICANTLY PROLONGED IN ELDERLY PERSONS, EVEN WHEN THEY ARE APPARENTLY HEALTHY. /QUINIDINE/

... EXCRETED IN URINE; ELIMINATION HALF-TIME IS ABOUT 6 HR. /QUINIDINE/

Quinidine generally has a plasma half-life of 6-8 hr in healthy individuals, but half-life may range from 3-16 hr or longer. In one study in patients with Plasmodium falciparum malaria, the elimination half-life of the drug averaged 12.8 hr (range: 6.6-24.8 hr).

Hepatotoxicity
Chronic therapy with quinidine is associated with a low rate of serum enzyme elevations, which are usually mild, asymptomatic and self limited even without alteration in dose. In addition, there have been many reports of acute hypersensitivity reactions to quinidine that include hepatic involvement. The reactions usually arise after 1 to 2 weeks of therapy, but can appear within 24 hours of restarting quinidine or with rechallenge. The clinical features are marked by fatigue, nausea, vomiting, diffuse muscle aches, arthralgias and high fever. Blood testing at an early stage shows increases in serum aminotransferase and alkaline phosphatase levels as well as mild jaundice, which can deepen for a few days even after stopping quinidine. The pattern of serum enzymes elevations is typically cholestatic or mixed. Rash is uncommon and eosinophilia is not typical, despite the presence of other signs of hypersensitivity (fever, arthralgias). Autoantibodies are not typically found. Liver biopsies usually show mild injury and small epithelioid granulomas, as are often found in many organs during systemic hypersensitivity reactions. A similar clinical signature of liver injury occurs with quinine, an optical isomer of quinidine that is used predominantly as an antimalarial agent. In recent years, there have been few reports of liver injury attributed to quinidine, probably because it is now rarely used.
Likelihood score: A (well established cause of clinically apparent liver injury).

---

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Limited information indicates that maternal doses of quinidine up to 1.8 grams daily produce low levels in milk and would not be expected to cause any adverse effects in breastfed infants, especially if the infant is older than 2 months. Exclusively breastfed infants should be carefully monitored if this drug is used during lactation, possibly including measurement of serum levels to rule out toxicity if there is a concern.

◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.

◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

---

View More

Adverse Effects
Occupational hepatotoxin - Secondary hepatotoxins: the potential for toxic effect in the occupational setting is based on cases of poisoning by human ingestion or animal experimentation.
Skin Sensitizer - An agent that can induce an allergic reaction in the skin.

---

Protein Binding
From 6.5 to 16.2 µmol/L, 80 to 88% of quinidine is bound to plasma proteins, mainly α1-acid glycoprotein and albumin. This fraction is lower in pregnant women, and it may be as low as 50 to 70% in infants and neonates.

---

Toxicity Summary
IDENTIFICATION: Quinidine is a class lA antiarrhythmic drug. Origin of the substance: Quinidine is the d- isomer of quinine. Quinidine is an alkaloid that may be derived from various species of Cinchona. Cinchona barks contain 0.25 to 3.0% quinidine. Quinidine is also prepared from quinine. Quinidine is a powder or white crystals, odorless with a bitter taste. Quinidine bisulfate is colorless crystals which is odorless and has a bitter taste. Quinidine gluconate is a white powder which is odorless and has a bitter taste. Quinidine poly-galacturonate is a powder. Quinidine sulfate is a white powder or odorless crystals with a bitter taste. Indications: Description: Premature ventricular extrasystoles and ventricular tachycardia; supraventricular arrhythmia; maintenance of sinus rhythm after cardioversion of atrial flutter or fibrillation. HUMAN EXPOSURE: Main risks and target organs: Cardio-toxicity is the main risk of quinidine poisoning. Quinidine may induce central nervous system symptoms. Summary of clinical effects: Toxic effects appear within 2 - 4 hours after ingestion but the delay may vary according to the quinidine salt and to the preparation forms. Symptoms may include disturbances of cardiac rhythm (especially in patients with underlying cardiovascular disease), neurotoxicity and respiratory depression. Diagnosis: Cardiac disturbances: circulatory arrest, shock, conduction disturbances, ventricular arrhythmias, ECG changes, Neurological symptoms: tinnitus, drowsiness, syncope, coma, convulsions, delirium. Respiratory depression. Quinidine concentrations may be helpful in diagnosis but are not useful for clinical management. Contraindications: Allergy or idiosyncrasy to cinchona alkaloids; atrioventricular or complete heart block; intraventricular conduction defects; absence of atrial activity; digitalis intoxication; myasthenia gravis and ventricular dysrhythmia of the torsades de pointes type Precautions include the following: Congestive heart failure, hypotension, renal disease, hepatic failure; concurrent use of other antiarrhythmic drugs; old age and breast-feeding. Routes of entry: Oral: Oral absorption is the most frequent cause of intoxication. Parenteral: Intoxication after IV administration is rare but has been reported in patients treated with IV quinidine for cardiac dysrhythmia. Absorption by route of exposure: Oral: Quinidine is almost completely absorbed from the gastrointestinal tract. However, because of hepatic first-pass effect, the absolute bioavailability is about 70 to 80% of the ingested dose and may vary between patients and preparations. The time to plasma peak concentration is 1 to 3 hours for quinidine sulfate, 3 to 6 hours for quinidine gluconate and about 6 hours for quinidine polygalacturonate. Sustained-release quinidine is absorbed continuously over 8 to 12 hours. Parenteral: Absorption of quinidine after intramuscular injection may be erratic and unpredictable with incomplete absorption of the administered dose, probably due to precipitation of drug at the site of injection. Other studies indicate no difference between the rate of quinidine absorption when given by intramuscular injection or oral absorption. Distribution by route of exposure: Oral: Protein binding: About 70 to 80% of the drug is bound to plasma protein. Plasma protein binding is decreased in patients with chronic liver disease. Tissue: Quinidine concentrations in liver are 10 to 30 times higher than those in plasma. Skeletal and cardiac muscle, brain and other tissues contain intermediate amounts. The red cell plasma partition ratio is 0.82. Biological half-life by route of exposure: Elimination half-life: The half-life is about 6 to 7 hours. It is increased in chronic liver disease and in the elderly. It does not appear to be altered in congestive heart failure or renal failure. Metabolism: 50 to 90% of quinidine is metabolized in the liver to hydroxylated products. Metabolites include 3-hydroxyquinidine, 2 oxoquinidinone, 0-desmethylquinidine, quinidine-N-oxide. The principal metabolite is 3 hydroxyquinidine which exerts similar effects to quinidine and may account for part of the observed antiarrhythmic effects. The elimination kinetics of hydroxyquinidine appear to be similar to those of quinidine. Elimination by route of exposure Kidney: The amount excreted unchanged in urine is variable but is about 17% of an administered dose. Up to 50% of a dose of quinidine (unchanged + metabolites) is excreted in urine within 24 hours after administration. Renal excretion is dependent upon the pH of the urine. Excretion varies inversely with urine pH. Excretion is reduced in renal insufficiency and in congestive heart failure. Liver: 50 to 90% of a dose of quinidine is metabolized in the liver. Bile: Approximately 1 to 3% is excreted in the feces via the bile. Breast milk: Quinidine is excreted in breast milk. Mode of action Toxicodynamics: Quinidine reduces the permeability of heart muscle to electrolytes (membrane stabilizer) and is a general cardiac depressant. It has a negative inotropic effect; inhibits the spontaneous diastolic depolarization; slow conduction; lengthens the effective refractory period; and raises the electrical threshold. This results in depression of contractility, impaired conductivity (atrioventricular and intraventricular) and decreased excitability but with possible abnormal stimulus re-entry mechanism. Quinidine has an anticholinergic effect and peripheral vasodilator properties. In experimental studies the following progression changes was observed: ECG: bradycardia, prolongation of the PR interval, lengthening of the QT interval, widening of the QRS with development of an idioventricular rhythm and then in ventricular standstill. Sometimes the terminal event was ventricular fibrillation. Blood pressure decreases progressively. A significant decrease of blood pressure was noted with the appearance of QRS widening and blood pressure was close to zero when slow idioventricular rhythm appeared. Electrolytes abnormalities: decrease in plasma concentrations of potassium, sodium and magnesium with the development of acidosis. Electrolytes: Hypokalaemia may occur and is probably related to an intracellular transport of potassium by a direct effect on cellular membrane permeability. Neurologic symptoms: Syncope and convulsions may represent a direct toxic effect on CNS or may be related to cerebral ischaemia due to circulatory or respiratory failure. Pharmacodynamics: Quinidine slows the rate of firing of the normal and of ectopic rhythmic foci; it raises the threshold for electrically induced arrhythmias; it protects against ventricular arrhythmias; and it prevents or terminates circus movement flutter. Teratogenicity: Quinidine has been implicated as a cause of light cranial nerve damage to the fetus at doses much larger than those needed to treat arrhythmias. Interactions: Several interactions have been reported. Quinidine has a synergistic action with warfarin (decrease of prothrombin level). Quinidine potentiates both non-depolarizing and depolarizing neuromuscular blocking agents. The cardiodepressant effects of other antiarrhythmic agents are increased by concurrent use of quinidine; amiodarone increases quinidine concentrations in the blood. Quinidine concentrations are reduced by: rifampicin, anticonvulsants, nifedipine and acetazolamide. Quinidine concentrations are increased by antacids, cimetidine, verapamil and amiodarone; the risk of quinidine toxicity is increased by terfenadine, astemizole, and thiazide and loop diuretics. Quinidine increases the plasma concentrations of propafenone and digoxin. Main adverse effects: Numerous adverse effects during quinidine therapy have been reported. Cardiovascular: Hypotension after IV administration; Syncope; proarrhythmic effect: "torsades de pointes"; and ECG: widening of QRS interval; prolongation of PR and QT intervals. CNS: Cinchonism: headache, fever, visual disturbances, mydriasis, tinnitus, nausea, vomiting and rashes. Gastrointestinal: Nausea, vomiting, diarrhoea, colic have been reported. Hepatic: Granulomatous hepatitis or hepatitis with centrilobular necrosis. Skin: Skin rashes with drug fever and photosensitivity may result. Hematologic: Thrombocytopenia (immunologic reaction) has been noted. Clinical effects: Acute poisoning: Ingestion: Severity of quinidine poisoning is related to the cardiotoxic effects. Symptoms appear usually within 2 to 4 hours and may include: cardiovascular symptoms: hypotension, cardiogenic shock, cardiac arrest. ECG may show: decrease of T wave; prolongation of QT and QRS intervals; atrioventricular block; ventricular dysrhythmia (torsade de pointes). Neurological symptoms: tinnitus, drowsiness, syncope, coma, convulsion, blurred vision and diplopia. Respiratory symptoms: hypoventilation and apnea. Cardiotoxicity may be enhanced if other cardiotoxic drugs have been ingested (antiarrhythmic drugs, tricyclic antidepressants). Parenteral exposure: After IV administration symptoms appear more rapidly. Chronic poisoning: Ingestion: The most relevant symptoms of chronic poisoning are: ECG disturbances; syncope due to ventricular dysrhythmia, (torsade de pointes) and cinchonism gastrointestinal disturbances Course, prognosis, cause of death: The usual course of quinidine poisoning is dominated by the cardiovascular disturbances which usually occur within 2 to 4 first hours but may first appear as late as 12 hours after exposure (and perhaps even later after ingestion of a slow- release preparation). Symptoms may last for 24 to 36 hours. Patients who survive 48 hours after acute poisoning are likely to recover. Death may result from cardiac arrest by asystole or electromechanical dissociation and, rarely, by ventricular fibrillation. Systematic description of clinical effects: Cardiovascular: Acute: Cardiovascular symptoms are the major features of quinidine toxicity. Tachycardia due to anticholinergic effects is usually observed initially or in moderate intoxication. In severe intoxication, bradycardia due to atrioventricular block may occur. Hypotension and shock: hypotension due to peripheral vasodilation is common. In severe intoxication, cardiogenic shock with increased central venous pressure is usually observed and is related to decreased cardiac contractility. Cardiac arrest may occur, which may be related to electromechanical dissociation, ventricular dysrhythmia or asystole. Cardiac dysrhythmias are common and may include: atrioventricular block, idioventricular rhythm, ventricular tachycardia and fibrillation, torsades de pointes. ECG changes are always present in symptomatic intoxication: repolarization abnormalities, decreased T wave, increase of U wave, prolongation of QT and PR intervals, widening of QRS complexes (> 0.08 sec), atrioventricular block. Syncope due to torsade de pointes may occur. Chronic: ECG changes with repolarization abnormalities, decreased T wave and increase of QT interval are a common feature during quinidine therapy. Syncope is related to transient torsade de pointes and occurs in 1 to 8% of patients receiving quinidine. The occurrence of torsade de pointes is not correlated with plasma quinidine levels but is favored by an increase in the QT interval. Respiratory: Acute: Respiratory depression or apnea is mostly associated with severe cardiac disturbances such as shock or ventricular dysrhythmia. Pulmonary edema with normal pulmonary capillary wedge pressure following an attempted suicide has been documented. Neurological: CNS: Acute: Drowsiness, delirium, coma and convulsions may appear without cardiac symptoms. However, cardiac failure should always be considered when CNS symptoms appear. Cinchonism may sometimes appear. Chronic: Cinchonism. Delirium has been reported. Peripheral nervous system: Chronic: Quinidine can potentiate the neuromuscular blocking action of some skeletal muscle relaxants and may cause the return of respiratory paralysis if it is given shortly after recovery from neuromuscular blockade. Autonomic nervous system: Acute: Quinidine has an anticholinergic effect. However, this effect is usually limited to the vagal system. Skeletal and smooth muscle: Chronic: An increase in serum concentrations of skeletal muscle enzymes has been reported in a man treated with quinidine. Gastrointestinal: Acute: Nausea and vomiting may occur. Chronic: Gastrointestinal toxicity (nausea, vomiting, diarrhea and colic) is the most frequent side effect of quinidine. Hepatic: Chronic: Hepatotoxicity has been reported, with an increase in serum concentrations of transaminases, LDH, alkaline phosphatase, and cholestasis. Renal: Acute: No direct nephrotoxic effect has been reported. Acute renal failure related to cardiogenic shock may occur. Dermatological: Chronic: Skin lesions have been attributed to the use of quinidine and include skin rash, photosensitivity and lichen planus. Eye, ear, nose, throat: local effects: Acute: Cinchonism is rarely observed in acute poisonings. Toxic amblyopia, scotoma and impaired color perception may occur at toxic doses. Chronic: Chronic cumulative overdose may cause cinchonism: headache, tinnitus, vertigo, mydriasis, blurred vision, diplopia, photophobia, deafness, and corneal deposits have been reported in a patient who took quinidine for two years. Hematological: Chronic: Thrombocytopenia and hemolytic anemia of immunologic origins have been reported. Immunological: Chronic: Quinidine may cause several immunologic mediated reactions: thrombocytopenia, hemolytic anemia, angioneurotic edema, skin rash, fever. Metabolic: Acid-base disturbances: Acute: Metabolic acidosis may occur in severe intoxication with shock. Fluid and electrolyte disturbances: Acute: Hypokalemia is frequently observed. Special risks: Pregnancy: Chronic: Quinidine has been implicated as a cause of cranial nerve damage to the fetus at doses much larger than those needed to treat arrhythmia. In a neonate born to a woman taking quinidine throughout pregnancy, serum levels were equal to that of the mother. The child's ECG was normal and there was no evidence of teratogenicity. Breast-feeding: Chronic: Quinidine is present in breast milk at levels slightly lower than serum levels. The dose of quinidine received by an infant taking 1l of milk would be below therapeutic doses. However, breast-feeding is not recommended because of potential quinidine accumulation in the immature newborn liver.

---

IDENTIFICATION: Quinidine is a class lA antiarrhythmic drug. Origin of the substance: Quinidine is the d- isomer of quinine. Quinidine is an alkaloid that may be derived from various species of Cinchona. Cinchona barks contain 0.25 to 3.0% quinidine. Quinidine is also prepared from quinine. Quinidine is a powder or white crystals, odorless with a bitter taste. Quinidine bisulfate is colorless crystals which is odorless and has a bitter taste. Quinidine gluconate is a white powder which is odorless and has a bitter taste. Quinidine poly-galacturonate is a powder. Quinidine sulfate is a white powder or odorless crystals with a bitter taste. Indications: Description: Premature ventricular extrasystoles and ventricular tachycardia; supraventricular arrhythmia; maintenance of sinus rhythm after cardioversion of atrial flutter or fibrillation. HUMAN EXPOSURE: Main risks and target organs: Cardio-toxicity is the main risk of quinidine poisoning. Quinidine may induce central nervous system symptoms. Summary of clinical effects: Toxic effects appear within 2 - 4 hours after ingestion but the delay may vary according to the quinidine salt and to the preparation forms. Symptoms may include disturbances of cardiac rhythm (especially in patients with underlying cardiovascular disease), neurotoxicity and respiratory depression. Diagnosis: Cardiac disturbances: circulatory arrest, shock, conduction disturbances, ventricular arrhythmias, ECG changes, Neurological symptoms: tinnitus, drowsiness, syncope, coma, convulsions, delirium. Respiratory depression. Quinidine concentrations may be helpful in diagnosis but are not useful for clinical management. Contraindications: Allergy or idiosyncrasy to cinchona alkaloids; atrioventricular or complete heart block; intraventricular conduction defects; absence of atrial activity; digitalis intoxication; myasthenia gravis and ventricular dysrhythmia of the torsades de pointes type Precautions include the following: Congestive heart failure, hypotension, renal disease, hepatic failure; concurrent use of other antiarhythmic drugs; old age and breast-feeding. Routes of entry: Oral: Oral absorption is the most frequent cause of intoxication. Parenteral: Intoxication after IV administration is rare but has been reported in patients treated with IV quinidine for cardiac dysrhythmia. Absorption by route of exposure: Oral: Quinidine is almost completely absorbed from the gastrointestinal tract. However, because of hepatic first-pass effect, the absolute bioavailability is about 70 to 80% of the ingested dose and may vary between patients and preparations. The time to plasma peak concentration is 1 to 3 hours for quinidine sulfate, 3 to 6 hours for quinidine gluconate and about 6 hours for quinidine polygalacturonate. Sustained-release quinidine is absorbed continuously over 8 to 12 hours. Parenteral: Absorption of quinidine after intramuscular injection may be erratic and unpredictable with incomplete absorption of the administered dose, probably due to precipitation of drug at the site of injection. Other studies indicate no difference between the rate of quinidine absorption when given by intramuscular injection or oral absorption. Distribution by route of exposure: Oral: Protein binding: About 70 to 80% of the drug is bound to plasma protein. Plasma protein binding is decreased in patients with chronic liver disease. Tissue: Quinidine concentrations in liver are 10 to 30 times higher than those in plasma. Skeletal and cardiac muscle, brain and other tissues contain intermediate amounts. The red cell plasma partition ratio is 0.82. Biological half-life by route of exposure: Elimination half-life: The half-life is about 6 to 7 hours. It is increased in chronic liver disease and in the elderly. It does not appear to be altered in congestive heart failure or renal failure. Metabolism: 50 to 90% of quinidine is metabolized in the liver to hydroxylated products. Metabolites include 3-hydroxyquinidine, 2 oxoquinidinone, 0-desmethylquinidine, quinidine-N-oxide. The principal metabolite is 3 hydroxyquinidine which exerts similar effects to quinidine and may account for part of the observed antiarrhythmic effects. The elimination kinetics of hydroxyquinidine appear to be similar to those of quinidine. Elimination by route of exposure Kidney: The amount excreted unchanged in urine is variable but is about 17% of an administered dose. Up to 50% of a dose of quinidine (unchanged + metabolites) is excreted in urine within 24 hours after administration. Renal excretion is dependent upon the pH of the urine. Excretion varies inversely with urine pH. Excretion is reduced in renal insufficiency and in congestive heart failure. Liver: 50 to 90% of a dose of quinidine is metabolized in the liver. Bile: Approximately 1 to 3% is excreted in the feces via the bile. Breast milk: Quinidine is excreted in breast milk. Mode of action Toxicodynamics: Quinidine reduces the permeability of heart muscle to electrolytes (membrane stabilizer) and is a general cardiac depressant. It has a negative inotropic effect; inhibits the spontaneous diastolic depolarization; slow conduction; lengthens the effective refractory period; and raises the electrical threshold. This results in depression of contractility, impaired conductivity (atrioventricular and intraventricular) and decreased excitability but with possible abnormal stimulus re-entry mechanism. Quinidine has an anticholinergic effect and peripheral vasodilator properties. In experimental studies the following progression changes was observed: ECG: bradycardia, prolongation of the PR interval, lengthening of the QT interval, widening of the QRS with development of an idioventricular rhythm and then in ventricular standstill. Sometimes the terminal event was ventricular fibrillation. Blood pressure decreases progressively. A significant decrease of blood pressure was noted with the appearance of QRS widening and blood pressure was close to zero when slow idioventricular rhythm appeared. Electrolytes abnormalities: decrease in plasma concentrations of potassium, sodium and magnesium with the development of acidosis. Electrolytes: Hypokalaemia may occur and is probably related to an intracellular transport of potassium by a direct effect on cellular membrane permeability. Neurologic symptoms: Syncope and convulsions may represent a direct toxic effect on CNS or may be related to cerebral ischaemia due to circulatory or respiratory failure. Pharmacodynamics: Quinidine slows the rate of firing of the normal and of ectopic rhythmic foci; it raises the threshold for electrically induced arrhythmias; it protects against ventricular arrhythmias; and it prevents or terminates circus movement flutter. Teratogenicity: Quinidine has been implicated as a cause of light cranial nerve damage to the fetus at doses much larger than those needed to treat arrhythmias. Interactions: Several interactions have been reported. Quinidine has a synergistic action with warfarin (decrease of prothrombin level). Quinidine potentiates both non-depolarizing and depolarizing neuromuscular blocking agents. The cardiodepressant effects of other antiarrhythmic agents are increased by concurrent use of quinidine; amiodarone increases quinidine concentrations in the blood. Quinidine concentrations are reduced by: rifampicin, anticonvulsants, nifedipine and acetazolamide. Quinidine concentrations are increased by antacids, cimetidine, verapamil and amiodarone; the risk of quinidine toxicity is increased by terfenadine, astemizole, and thiazide and loop diuretics. Quinidine increases the plasma concentrations of propafenone and digoxin. Main adverse effects: Numerous adverse effects during quinidine therapy have been reported. Cardiovascular: Hypotension after IV administration; Syncope; proarrhythmic effect: "torsades de pointes"; and ECG: widening of QRS interval; prolongation of PR and QT intervals. CNS: Cinchonism: headache, fever, visual disturbances, mydriasis, tinnitus, nausea, vomiting and rashes. Gastrointestinal: Nausea, vomiting, diarrhoea, colic have been reported. Hepatic: Granulomatous hepatitis or hepatitis with centrilobular necrosis. Skin: Skin rashes with drug fever and photosensitivity may result. Hematologic: Thrombocytopenia (immunologic reaction) has been noted. Clinical effects: Acute poisoning: Ingestion: Severity of quinidine poisoning is related to the cardiotoxic effects. Symptoms appear usually within 2 to 4 hours and may include: cardiovascular symptoms: hypotension, cardiogenic shock, cardiac arrest. ECG may show: decrease of T wave; prolongation of QT and QRS intervals; atrioventricular block; ventricular dysrhythmia (torsade de pointes). Neurological symptoms: tinnitus, drowsiness, syncope, coma, convulsion, blurred vision and diplopia. Respiratory symptoms: hypoventilation and apnea. Cardiotoxicity may be enhanced if other cardiotoxic drugs have been ingested (antiarrhythmic drugs, tricyclic antidepressants). Parenteral exposure: After IV administration symptoms appear more rapidly. Chronic poisoning: Ingestion: The most relevant symptoms of chronic poisoning are: ECG disturbances; syncope due to ventricular dysrhythmia, (torsade de pointes) and cinchonism gastrointestinal disturbances Course, prognosis, cause of death: The usual course of quinidine poisoning is dominated by the cardiovascular disturbances which usually occur within 2 to 4 first hours but may first appear as late as 12 hours after exposure (and perhaps even later after ingestion of a slow- release preparation). Symptoms may last for 24 to 36 hours. Patients who survive 48 hours after acute poisoning are likely to recover. Death may result from cardiac arrest by asystole or electromechanical dissociation and, rarely, by ventricular fibrillation. Systematic description of clinical effects: Cardiovascular: Acute: Cardiovascular symptoms are the major features of quinidine toxicity. Tachycardia due to anticholinergic effects is usually observed initially or in moderate intoxication. In severe intoxication, bradycardia due to atrioventricular block may occur. Hypotension and shock: hypotension due to peripheral vasodilation is common. In severe intoxication, cardiogenic shock with increased central venous pressure is usually observed and is related to decreased cardiac contractility. Cardiac arrest may occur, which may be related to electromechanical dissociation, ventricular dysrhythmia or asystole. Cardiac dysrhythmias are common and may include: atrioventricular block, idioventricular rhythm, ventricular tachycardia and fibrillation, torsades de pointes. ECG changes are always present in symptomatic intoxication: repolarization abnormalities, decreased T wave, increase of U wave, prolongation of QT and PR intervals, widening of QRS complexes (> 0.08 sec), atrioventricular block. Syncope due to torsade de pointes may occur. Chronic: ECG changes with repolarization abnormalities, decreased T wave and increase of QT interval are a common feature during quinidine therapy. Syncope is related to transient torsade de pointes and occurs in 1 to 8% of patients receiving quinidine. The occurrence of torsade de pointes is not correlated with plasma quinidine levels but is favored by an increase in the QT interval. Respiratory: Acute: Respiratory depression or apnea is mostly associated with severe cardiac disturbances such as shock or ventricular dysrhythmia. Pulmonary edema with normal pulmonary capillary wedge pressure following an attempted suicide has been documented. Neurological: CNS: Acute: Drowsiness, delirium, coma and convulsions may appear without cardiac symptoms. However, cardiac failure should always be considered when CNS symptoms appear. Cinchonism may sometimes appear. Chronic: Cinchonism. Delirium has been reported. Peripheral nervous system: Chronic: Quinidine can potentiate the neuromuscular blocking action of some skeletal muscle relaxants and may cause the return of respiratory paralysis if it is given shortly after recovery from neuromuscular blockade. Autonomic nervous system: Acute: Quinidine has an anticholinergic effect. However, this effect is usually limited to the vagal system. Skeletal and smooth muscle: Chronic: An increase in serum concentrations of skeletal muscle enzymes has been reported in a man treated with quinidine. Gastrointestinal: Acute: Nausea and vomiting may occur. Chronic: Gastrointestinal toxicity (nausea, vomiting, diarrhea and colic) is the most frequent side effect of quinidine. Hepatic: Chronic: Hepatotoxicity has been reported, with an increase in serum concentrations of transaminases, LDH, alkaline phosphatase, and cholestasis. Renal: Acute: No direct nephrotoxic effect has been reported. Acute renal failure related to cardiogenic shock may occur. Dermatological: Chronic: Skin lesions have been attributed to the use of quinidine and include skin rash, photosensitivity and lichen planus. Eye, ear, nose, throat: local effects: Acute: Cinchonism is rarely observed in acute poisonings. Toxic amblyopia, scotoma and impaired color perception may occur at toxic doses. Chronic: Chronic cumulative overdose may cause cinchonism: headache, tinnitus, vertigo, mydriasis, blurred vision, diplopia, photophobia, deafness, and corneal deposits have been reported in a patient who took quinidine for two years. Hematological: Chronic: Thrombocytopenia and hemolytic anemia of immunologic origins have been reported. Immunological: Chronic: Quinidine may cause several immunologic mediated reactions: thrombocytopenia, hemolytic anemia, angioneurotic edema, skin rash, fever. Metabolic: Acid-base disturbances: Acute: Metabolic acidosis may occur in severe intoxication with shock. Fluid and electrolyte disturbances: Acute: Hypokalemia is frequently observed. Special risks: Pregnancy: Chronic: Quinidine has been implicated as a cause of cranial nerve damage to the fetus at doses much larger than those needed to treat arrhythmia. In a neonate born to a woman taking quinidine throughout pregnancy, serum levels were equal to that of the mother. The child's ECG was normal and there was no evidence of teratogenicity. Breast-feeding: Chronic: Quinidine is present in breast milk at levels slightly lower than serum levels. The dose of quinidine received by an infant taking 1l of milk would be below therapeutic doses. However, breast-feeding is not recommended because of potential quinidine accumulation in the immature newborn liver. /Quinidine/ International Programme on Chemical Safety; Poisons Information Monograph: Quinidine (PIM 463) (1990) Available from, as of April 7, 2009: https://www.inchem.org/pages/pims.html

[1]. Wrighton DC, et al. Mechanism of inhibition of mouse Slo3 (KCa 5.1) potassium channels by quinine, quinidine and barium. Br J Pharmacol. 2015 Sep;172(17):4355-63.
[2]. Cheng KI, et al. Application of quinidine on rat sciatic nerve decreases the amplitude and increases the latency of evoked responses. J Anesth. 2014 Aug;28(4):559-68

Quinidine is a cinchona alkaloid consisting of cinchonine with the hydrogen at the 6-position of the quinoline ring substituted by methoxy. It has a role as an alpha-adrenergic antagonist, an antimalarial, an anti-arrhythmia drug, a sodium channel blocker, a muscarinic antagonist, a potassium channel blocker, a P450 inhibitor, an EC 1.14.13.181 (13-deoxydaunorubicin hydroxylase) inhibitor, an EC 3.6.3.44 (xenobiotic-transporting ATPase) inhibitor and a drug allergen. It derives from a hydride of a cinchonan.

---

Quinidine is a D-isomer of [quinine] present in the bark of the Cinchona tree and similar plant species. This alkaloid was first described in 1848 and has a long history as an antiarrhythmic medication. Quinidine is considered the first antiarrhythmic drug (class Ia) and is moderately efficacious in the acute conversion of atrial fibrillation to normal sinus rhythm. It prolongs cellular action potential by blocking sodium and potassium currents. A phenomenon known as “quinidine syncope” was first described in the 1950s, characterized by syncopal attacks and ventricular fibrillation in patients treated with this drug. Due to its side effects and increased risk of mortality, the use of quinidine was reduced over the next few decades. However, it continues to be used in the treatment of Brugada syndrome, short QT syndrome and idiopathic ventricular fibrillation.

---

Quinidine is an Antiarrhythmic and Cytochrome P450 2D6 Inhibitor. The mechanism of action of quinidine is as a Cytochrome P450 2D6 Inhibitor.
Quinidine is a natural cinchona alkaloid which has potent antiarrhythmic activity and has been used for decades in the treatment of atrial and ventricular arrhythmias. Quinidine has been associated with fever, mild jaundice and clinically apparent liver injury in up to 2% of treated patients.

---

Quinidex has been reported in Cinchona calisaya, Ciliosemina pedunculata, and other organisms with data available.
Quinidine Sulfate is the sulfate salt form of quinidine, an alkaloid with antimalarial and antiarrhythmic (Class la) properties. Quinidine sulfate exerts its anti-malarial activity by acting primarily as an intra-erythrocytic schizonticide through association with the hemepolymer (hemozoin) in the acidic food vacuole of the parasite thereby preventing further polymerization by heme polymerase enzyme. This results in accumulation of toxic heme and death of the parasite. Quinidine sulfate exerts its antiarrhythmic effects by depressing the flow of sodium ions into cells during phase 0 of the cardiac action potential, thereby slowing the impulse conduction through the atrioventricular (AV) node, reducing the rate of phase 0 depolarization and prolonging the refractory period. Quinidine sulfate also reduces the slope of phase 4 depolarization in Purkinje-fibres resulting in slowed conduction and reduced automaticity in the heart.

---

View More

Quinidine is an alkaloid extracted from the bark of the Cinchona tree with class 1A antiarrhythmic and antimalarial effects. Quinidine stabilizes the neuronal membrane by binding to and inhibiting voltage-gated sodium channels, thereby inhibiting the sodium influx required for the initiation and conduction of impulses resulting in an increase of the threshold for excitation and decreased depolarization during phase 0 of the action potential. In addition, the effective refractory period (ERP), action potential duration (APD), and ERP/APD ratios are increased, resulting in decreased conduction velocity of nerve impulses. Quinidine exerts its antimalarial activity by acting primarily as an intra-erythrocytic schizonticide through association with the heme polymer (hemazoin) in the acidic food vacuole of the parasite thereby preventing further polymerization by heme polymerase enzyme. This results in accumulation of toxic heme and death of the parasite.

---

An optical isomer of quinine, extracted from the bark of the CHINCHONA tree and similar plant species. This alkaloid dampens the excitability of cardiac and skeletal muscles by blocking sodium and potassium currents across cellular membranes. It prolongs cellular ACTION POTENTIALS, and decreases automaticity. Quinidine also blocks muscarinic and alpha-adrenergic neurotransmission.

---

Drug Indication
Quinidine is indicated for the management and prophylactic therapy of atrial fibrillation/flutter, as well as the suppression of recurrent documented ventricular arrhythmias. It is also used in the treatment of Brugada syndrome, short QT syndrome and idiopathic ventricular fibrillation.

---

Therapeutic Uses
Adrenergic alpha-Antagonists; Anti-Arrhythmia Agents; Antimalarials; Enzyme Inhibitors; Muscarinic Antagonists

Quinidine is indicated in the treatment of recurrent, documented, life-threatening ventricular arrhythmias, such as sustained ventricular tachycardia. Quinidine should not be used to treat ventricular arrhythmias of lesser severity, such as asymptomatic ventricular premature contractions. /Included in US product labeling/

Quinidine is indicated in the treatment of symptomatic atrial fibrillation or flutter in patients whose symptoms are not controlled by measures to reduce the rate of ventricular response. /US Product Labeling/

Chronic quinidine treatment is indicated for some patients at high risk for symptomatic atrial fibrillation pr flutter, such as those who have had previous episodes taht are so frequent and poorly tolerated as to outweigh the risk of porphylactic therapy with quinidine.

---

Drug Warnings
Skin reactions to quinidine are rare and include morbilliform and scarlatiniformeruptions, urticaria, rash, pruritus, exfoliative dermatitis, eczema, severe exacerbation of psoriasis, lichenoid reactions, flushing, pigmentary abnormalities, photodermatitis (photosensitivity), and contact dermatitis.

... Adverse reactions are not related to plasma concentration and include drug fever cholestatic hepatitis, systemic lupus erythematosus, asthma, anaphylaxis, thrombocytopenia, hemolytic anemia (especially in glutcose-6-phosphate dehydrogenase deficiency), and hypoprothrombinemia. Skin changes range from maculopapular eruption to thrombocytopenic purpura, cutaneous vasculitis, photosensitivity, and bullous lesions.

Drug induced agranulocytosisis a clinical entity characterized by a selective reduction of circulating neutrophils, usually to a level less than 0.2X10+9/l in relation to the administration of the drug. Quinidine is an antiarrhythmic agent widely used on an outpatient basis with some well known hematological side effects. Its midterm administration has been related to a few cases of agranulocytosis. The case of a 60 yr old man with atrial fibrillation is described who presented quinidine induced agranulocytosis of abrupt onset only 3 days after the exposure to the drug, recovering normal levels of neutrophils during the third hospitalization day.

---

Pharmacodynamics
Quinidine is an antimalarial schizonticide, and a class Ia antiarrhythmic agent used to interrupt or prevent reentrant arrhythmias and arrhythmias due to increased automaticity, such as atrial flutter, atrial fibrillation, and paroxysmal supraventricular tachycardia. In most patients, quinidine can lead to an increase in the sinus rate. Quinidine also causes a marked prolongation of the QT interval in a dose-related manner, acts peripherally as an α-adrenergic antagonist, and has anticholinergic and negative inotropic activity. The QT interval prolongation caused by quinidine can lead to increased ventricular automaticity and polymorphic ventricular tachycardias, such as _torsades de pointes_. The risk of _torsades_ is increased by bradycardia, hypokalemia, hypomagnesemia or high serum levels of quinidine. However, this type of rhythm disturbance may appear in the absence of any of them. Patients treated with quinidine may also be at risk of a paradoxical increase in ventricular rate in atrial flutter/fibrillation, and patients with sick sinus syndrome treated with quinidine may develop marked sinus node depression and bradycardia.

---

Mechanism of Action
Quinidine has a complex electrophysiological profile that has not been fully elucidated. The antiarrhythmic actions of this drug are mediated through effects on sodium channels in Purkinje fibers. Quinidine blocks the rapid sodium channel (INa), decreasing the phase zero of rapid depolarization of the action potential. Quinidine also reduces repolarizing K+ currents (IKr, IKs), the inward rectifier potassium current (IK1), and the transient outward potassium current Ito, as well as the L-type calcium current ICa and the late INa inward current. The reduction of these currents leads to the prolongation of the action potential duration. By shortening the plateau but prolonging late depolarization, quinidine facilitates the formation of early afterdepolarisation (EAD). Additionally, in patients with malaria, quinidine acts primarily as an intra-erythrocytic schizonticide, and is gametocidal to _Plasmodium vivax_ and _P. malariae_, but not to _P. falciparum_.

The exact mechanism of antiarrhythmic action of quinidine has not been determined conclusively, but the drug is considered a class I (membrane stabilizing) antiarrhythmic agent. Like other class I antiarrhythmic agents, quinidine is believed to combine with fast sodium channels in their inactive state and thereby inhibit recovery after repolarization in a time- and voltage-dependent manner, which is associated with subsequent dissociation of the drug from the sodium channels. Quinidine exhibits electrophysiologic effects characteristic of class IA antiarrhythmic agents. The electrophysiologic characteristics of the subgroups of class I antiarrhythmic agents may be related to quantitative differences in their rates of attachment to and dissociation from transmembrane sodium channels, with class IA agents exhibiting intermediate rates of attachment and dissociation.

Like lidocaine and procainamide, quinidine suppresses automaticity in the His-Purkinje system. In usual doses, quinidine may decrease the automaticity of ectopic pacemakers, but the extent of this effect also depends upon the anticholinergic effect of the drug on the sinoatrial node, atria, and atrioventricular node. Extremely high concentrations of quinidine may increase myocardial automaticity. The drug decreases conduction velocity in the atria, ventricles, and His-Purkinje system, and may decrease or cause no change in conduction velocity through the AV node. Quinidine probably suppresses atrial fibrillation or flutter by prolonging the effective refractory period and increasing the action potential duration in atrial and ventricular muscle and in the His-Purkinje system. Because prolongation of the effective refractory period is greater than the increase in the duration of the action potential, the cardiac tissue remains refractory even after restoration of the resting membrane potential. Quinidine shortens the effective refractory period of the atrioventricular node, and the anticholinergic action of the drug may also increase the conductivity of the atrioventricular node. The effects of quinidine on refractoriness and the action potential duration of atrial fibers may be modified by the anticholinergic effects of the drug. Quinidine decreases cardiac excitability, both in diastole and in the relative refractory period, by increasing the threshold potential for electrical excitation. At therapeutic plasma concentrations, quinidine causes prolongation of the QRS complex and QT interval.

Quinidine also exhibits some antipyretic and oxytocic properties. Quinidine has a very weak curare-like action on the myoneural junction and also causes depression of skeletal muscle action potential.

Intravenous quinidine depresses contractility and decreases systemic vascular resistance primarily by alpha-adrenergic receptor blockade. High blood levels of quinidine increase left ventricular end-diastolic pressure through its negative inotropic effect. Cardiovascular collapse has resulted from depression of contractility.

Quindine primarily kills the schizont parasite at the asexual intra-erythrocytic cycle stage of the Plasmodium falciparum malaria protozoan parasite. Quinidine also kills the gametocyte parasite stages of Plasmodium malariae, Plasmodium vivax, and Plasmodium ovale.

C20H24N2O2.HCL.H2O

378.89298

378.171

6151-40-2

Quinidine (15% dihydroquinidine);56-54-2;Quinidine sulfate;50-54-4;Quinidine sulfate dihydrate;6591-63-5;Quinidine polygalacturonate;27555-34-6;Quinidine gluconic acid;7054-25-3

16219921

Typically exists as White to off-white solid at room temperature

495.9ºC at 760 mmHg

258-259ºC

253.7ºC

3.848

3

5

4

26

457

4

C=C[C@H]1C[N@](CC[C@H]1C2)[C@@]2([H])[C@@H](O)C3=CC=NC4=CC=C(OC)C=C34.[H]Cl.[H]O[H]

SGVZDMWHXVXUBY-KAIFKDDSSA-N

InChI=1S/C20H24N2O2.ClH.H2O/c1-3-13-12-22-9-7-14(13)10-19(22)20(23)16-6-8-21-18-5-4-15(24-2)11-17(16)18;;/h3-6,8,11,13-14,19-20,23H,1,7,9-10,12H2,2H3;1H;1H2/t13-,14-,19+,20-;;/m0../s1

(S)-[(2R,4S,5R)-5-ethenyl-1-azabicyclo[2.2.2]octan-2-yl]-(6-methoxyquinolin-4-yl)methanol;hydrate;hydrochloride

Quinidine hydrochloride monohydrate; 6151-40-2; Quinidine, monohydrochloride, monohydrate; Z1PDY5DB92; 6'-Methoxycinchonan-9-ol hydrochloride monohydrate; Cinchonan-9-ol, 6'-methoxy-, hydrochloride, hydrate (1:1:1), (9S)-; Cinchonan-9-ol, 6'-methoxy-, monohydrochloride, monohydrate, (9S)-; (S)-[(2R,4S,5R)-5-ethenyl-1-azabicyclo[2.2.2]octan-2-yl]-(6-methoxyquinolin-4-yl)methanol;hydrate;hydrochloride;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~100 mg/mL (~263.93 mM)
H2O : ~2.5 mg/mL (~6.60 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (6.60 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 2.5 mg/mL (6.60 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

---

View More

Solubility in Formulation 3: ≥ 2.5 mg/mL (6.60 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

 (Please use freshly prepared in vivo formulations for optimal results.)