Absorption, Distribution and Excretion
Orally administered daffodil is rapidly and completely absorbed from the gastrointestinal tract. The time to peak concentration (Tmax) for the immediate-release formulation is 1 hour; for the extended-release formulation, it is 3.5 hours. The peak plasma concentration (Cmax) of the 10 mg extended-release tablet is 17.3–21.6 ng/mL; the relative bioavailability of the 10 mg extended-release tablet relative to oral aqueous solution is 96%. Almost all doses and their metabolites are completely excreted by the kidneys after 24 hours. Urinary excretion rate is 96% (90% of the total dose is excreted unchanged); fecal excretion rate is 0.5%. The plasma concentration of the 10 mg extended-release tablet is 2.6 L/kg. Like other aminopyridines, 4-aminopyridine is rapidly absorbed from the gastrointestinal tract into the bloodstream. This compound is readily metabolized in the liver, and the metabolites are excreted in the urine. Following intravenous or oral administration, approximately 90% of the administered dose is excreted in the urine. Dafapyridine is rapidly and completely absorbed from the gastrointestinal tract. The bioavailability of daffopyridine extended-release tablets is 96% compared to readily reconstituted immediate-release daffopyridine (formerly known as aminopyridine (4-aminopyridine, 4-AP)) aqueous solution. Compared to the aqueous solution of this drug, daffopyridine extended-release tablets result in delayed absorption, a slower and lower rise in peak plasma concentration, but the extent of absorption (area under the concentration-time curve (AUC)) is unaffected. Plasma concentrations and AUC of daffopyridine increase in a dose-proportional manner. The pharmacokinetics of daffopyridine in adult patients with multiple sclerosis (MS) are similar to those in healthy adults. In adult patients aged 29–56 years with MS, the mean peak plasma concentration following a single 10 mg dose of daffopyridine extended-release tablets was 25.23 ng/mL, reached 3.92 hours post-dose. In healthy, fasting adults, peak plasma concentrations following a single 10 mg dose of the extended-release tablet ranged from 17.3 to 21.6 ng/mL, reached 3–4 hours post-administration. For more complete data on the absorption, distribution, and excretion of 4-aminopyridines (8 in total), please visit the HSDB record page. Metabolites/Metabolites: Because daffopyridine is not extensively metabolized in the liver, it is not expected that drugs affecting the cytochrome P450 enzyme system taken concurrently with daffopyridine will not interact. Metabolites include 3-hydroxy-4-aminopyridine and 3-hydroxy-4-aminopyridine sulfate, both of which are inactive. CYP2E1 is the enzyme responsible for the 3-hydroxylation of daffopyridine. Specific enzymes involved in the metabolism of daffopyridine have not been identified in experimental animals, but based on human microsomal studies, it is suggested that CYP2E1 may be responsible for the hydroxylation of daffopyridine in vivo. In rats, approximately 36% of the parent drug is cleared via first-pass metabolism in the liver. Dafapyridine is primarily metabolized via hydroxylation followed by sulfate conjugation. Two circulating metabolites, 3-hydroxy-4-aminopyridine and 3-hydroxy-4-aminopyridine sulfate, were detected in mouse, rat, rabbit, dog, and human plasma. Although these metabolites were detected in all species, their metabolism was more extensive in rats and dogs than in humans. 4-Aminopyridine-N-oxide was also confirmed as a circulating metabolite in mouse and rat plasma. Two unidentified metabolites were detected in human plasma; however, the radioactivity of these metabolites was <2%. Small amounts of dafpyridine are metabolized to 3-hydroxy-4-aminopyridine and 3-hydroxy-4-aminopyridine sulfate by cytochrome P-450 (CYP) isoenzymes. These metabolites have no pharmacological activity against potassium channels. In vitro studies have shown that CYP2E1 is the major enzyme in the 3-hydroxylation of dafpyridine; other unidentified CYP enzymes play minor roles in the 3-hydroxylation of the drug.
Dafopyridine is not extensively metabolized in the liver; therefore, other drugs affecting the cytochrome P450 enzyme system taken concurrently with dafopyridine are not expected to interact. 4-Aminopyridine is rapidly absorbed into the bloodstream from the gastrointestinal tract. It is readily broken down or metabolized in the liver, producing excretable compounds that are eliminated in the urine. Following intravenous and oral absorption, almost all metabolites are excreted in the urine. It does not concentrate or accumulate in the skin. 4-Aminopyridine is excreted in the urine and rapidly detoxified in the liver (T48, L1090). Metabolites include 3-hydroxy-4-aminopyridine and 3-hydroxy-4-aminopyridine sulfate, both of which are inactive. CYP2E1 is the enzyme responsible for the 3-hydroxylation of dafopyridine.
Elimination pathway: Almost all doses and its metabolites are completely excreted by the kidneys after 24 hours.
Urine (96%; 90% of the total dose is excreted unchanged);
Feces (0.5%)
Half-life: Immediate-release formulation = 3.5 hours;
Sustained-release formulation = 5.47 hours;
Biological half-life
Immediate-release formulation = 3.5 hours; Sustained-release formulation = 5.47 hours;
Elimination of dafamopyridine is similar in rats and dogs, with a plasma half-life of 1–2 hours, but slightly prolonged in humans.
The half-life of dafamopyridine is 5.2–6.5 hours. The half-life of 3-hydroxy-4-aminopyridine sulfate is 7.6 hours. /In humans/

Toxicity Summary
4-Aminopyridine blocks potassium ion channels, thereby increasing the release of acetylcholine (and possibly norepinephrine) at nerve endings (A316). In multiple sclerosis (MS), axons gradually demyelinate, leading to the exposure of potassium ion channels. This potassium leakage causes cell repolarization and reduces neuronal excitability. The overall effect is impaired neuromuscular transmission, as triggering action potentials becomes more difficult. Dafapyridine inhibits voltage-gated potassium ion channels in the central nervous system to maintain transmembrane potentials and prolong action potentials. In other words, daffopyridine acts to ensure that the available current is high enough to stimulate conduction in demyelinated axons in MS patients. Furthermore, it can promote neuromuscular and synaptic transmission by relieving conduction blockade in demyelinated axons. Hepatotoxicity
Elevated serum transaminases have occasionally occurred during treatment with daffopyridine, but there is no conclusive evidence that it is associated with clinically significant cases of liver injury. In a safety analysis of a pre-registration controlled trial of dapopyridine in 1922 patients with multiple sclerosis, no laboratory evidence of liver injury or hepatotoxicity was found. However, several cases of clinically significant liver injury have been reported in the published literature. However, in all cases, liver injury could not be convincingly attributed to dapopyridine. Probability score: E (Unproven, but suspected rare cause of clinically significant liver injury). Pregnancy and Lactation Effects ◉ Overview of Use During Lactation Since there is currently no information regarding the use of dapopyridine during lactation, alternative medications are recommended, especially for breastfed newborns or preterm infants. ◉ Effects on Breastfed Infants No relevant published information was found as of the revision date. ◉ Effects on Lactation and Breast Milk No relevant published information was found as of the revision date.

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Protein Binding
10 mg Extended-Release Tablets = 1-3% Protein BindingToxicity Data
Mice Oral LD50 = 19 mg/kg
LD50, Oral, Rats = 21 mg/kg
LD50: 20-29 mg/kg (Oral, Rats) (L1090)
LD50: 3.7 mg/kg (Oral, Dogs) (L1090)
LD50: 326 mg/kg (Skin, Rabbits) (L1090)

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Interactions
The inhibitory effect of morphine (0.1-1 uM) on sensory-evoked dorsal horn network responses in mouse spinal explants with attached dorsal root ganglia (DRG) was rapidly restored upon addition of 4-aminopyridine (4-AP; 0.1 mM), and the major components of these spinal responses were stably maintained in the presence of opioids. Furthermore, pretreatment of spinal dorsal root ganglion (DRG) explants with 0.1 mM 4-AP blocked the inhibitory effect of 0.1 μM morphine on DRG-induced dorsal horn responses, and the effects of 1–10 μM morphine were at least partially antagonized. Elevated Ca++ levels (5 μM) attenuated the inhibitory effect of 1–10 μM morphine on dorsal horn responses, and this effect was significantly enhanced in the presence of 4-AP—in some cultures, concentrations up to 100 μM of morphine were strongly antagonized during the 2-hour testing period. Receptor analysis showed that 0.1 mM 4-AP ± 5 mM Ca++ had no effect on the binding of stereospecific opioid receptors, indicating that the antagonistic effects of these drugs in our cultures do not occur at the opioid receptor level. Our in vitro study of the inhibitory effect of 4-aminopyridine (4-AP) on opioid-induced sensory dorsal horn network responses is significant for analyzing opioid analgesia. A recent report further confirmed that 4-AP can indeed reverse the analgesic effect of morphine in rats (determined by a tail-flick test). This study investigated the therapeutic effect of verapamil toxicity in mildly sedated dogs. Verapamil was administered via bolus injection (0.72 mg/kg) followed by continuous infusion (0.11 mg/kg/min), resulting in decreased cardiac output (CO), heart rate (HR), rate of change of left ventricular pressure (LV dP/dt), mean aortic pressure (AO), and stroke volume. In contrast, 4-aminopyridine (4-AP) increased heart rate, cardiac output, LV dP/dt, and mean aortic pressure. Administering 4-aminopyridine (4-AP) before verapamil administration can prevent verapamil toxicity. Compared to verapamil alone, administering 4-AP before verapamil significantly improves mean aortic pressure (P<0.001), cardiac output (P<0.01), and rate of change of left ventricular pressure (LV dP/dt) (P<0.01). In summary, there appears to be no single specific treatment for verapamil toxicity, but existing medications and 4-AP can partially correct this toxicity. Due to the increased risk of dose-related adverse reactions, dapapridine should not be used in patients taking other aminopyridine drugs (including ad hoc formulations); dapapridine was formerly known as fapralidine (4-aminopyridine, 4-AP). Any products containing fapralidine or 4-aminopyridine should be discontinued before starting dapapridine treatment, as they have the same active ingredient.

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Non-human toxicity values
Dog oral LD50: 3.7 mg/kg
Male rat oral LD50: 14 mg/kg
Mice oral LD50: 50 mg/kg
Female rat oral LD50: 22 mg/kg
For more non-human toxicity values (complete data) for 4-aminopyridine (out of 12), please visit the HSDB record page.

[1]. Sherratt, R.M., H. Bostock, and T.A. Sears, Effects of 4-aminopyridine on normal and demyelinated mammalian nerve fibres. Nature, 1980. 283(5747): p. 570-2.

[2]. Bouchard, R. and D. Fedida, Closed- and open-state binding of 4-aminopyridine to the cloned human potassium channel Kv1.5. J Pharmacol Exp Ther, 1995. 275(2): p. 864-76.

Therapeutic Uses

Potassium Channel Blocker

Ampuri (dapapyridine) is a potassium channel blocker indicated for the improvement of walking ability in patients with multiple sclerosis (MS). /US Product Label Includes/
Sales of dapapyridine are restricted; this drug is available only through certain specialty pharmacies.
Drug Warnings

Reports of rare allergic reactions in patients taking dapapyridine. If an allergic reaction or other serious allergic reaction occurs, dapapyridine should be discontinued immediately and not taken again.
Dapapyridine can cause seizures. Post-marketing reports indicate that most seizures occur in patients receiving the recommended dose of dapapyridine (usually within days to weeks after starting treatment) and in patients with no prior history of epilepsy. Some patients have taken other medications that may increase the risk of seizures or lower the seizure threshold; in addition, age-related renal dysfunction and the resulting elevated plasma dapapyridine concentrations may also increase the risk of seizures. Using high doses of dapoxetine (e.g., 15 or 20 mg twice daily) increases the risk of seizures. In an open-label extended study in patients with multiple sclerosis (MS), the incidence of seizures in the 15 mg twice daily dose group was more than 4 times higher than in the recommended dose group (10 mg twice daily). Dafapyridine is contraindicated in patients with a history of epilepsy. This drug has not been evaluated in patients with a history of epilepsy or EEG showing epileptiform activity; such patients have been excluded from clinical trials. The risk of seizures in patients with EEG showing epileptiform activity is unclear and may be significantly higher than observed in clinical trials. The incidence of urinary tract infection (UTI) is higher in patients taking dapoxetine (12%) than in patients taking placebo (8%). If a patient taking dapoxetine develops a UTI, evaluation and treatment should be performed based on clinical indications. For more complete data on drug warnings for 4-aminopyridine (12 of 12), please visit the HSDB record page.

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Pharmacodynamics
Dafopyridine is a broad-spectrum lipophilic potassium channel blocker with a stronger binding affinity to open potassium channels in the central nervous system compared to their closed state. Its pharmacological target is the potassium channels exposed in patients with multiple sclerosis. It does not prolong the QTc interval.

C5H6N2

94.11454

94.053

504-24-5

1727

White to off-white solid powder

1.1±0.1 g/cm3

192.7±40.0 °C at 760 mmHg

157 °C

70.3±27.3 °C

0.5±0.4 mmHg at 25°C

1.569

-2.24

1

2

0

7

48

0

NC1=CC=NC=C1

NUKYPUAOHBNCPY-UHFFFAOYSA-N

InChI=1S/C5H6N2/c6-5-1-3-7-4-2-5/h1-4H,(H2,6,7)

pyridin-4-amine

Fampridine; Pyridin-4-amine; 4-aminopyridine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

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

DMSO : ≥ 50 mg/mL (~531.29 mM)
H2O : ~50 mg/mL (~531.29 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (26.56 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.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (26.56 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.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (26.56 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.

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