5-HT_1A Receptor ( IC50 = 450 nM ); 5-HT_1B Receptor ( IC50 = 40 nM ); 5-HT_2A Receptor ( IC50 = 4 nM ); 5-HT_2B Receptor ( IC50 = 40 nM );
5-HT_2C Receptor ( IC50 = 6 nM ); H₁ Receptor ( IC50 = 1.1 nM ); H₃ Receptor ( IC50 = 1 μM ); H₄ Receptor ( IC50 = 33.6 nM );
SERT ( Ki = 3.45 nM ); NET ( Ki = 13.3 nM ); DAT ( Ki = 2.58 μM ); Adrenergic receptor ( IC50 = 24 nM ); muscarinic receptor ( IC50 = 7.2 nM ); TrkA; TrkB
Amitriptyline HCl (Elavil) is a potent inhibitor of the 5-hydroxytryptamine transporter (SERT) and noradrenaline transporter (NET). In rat brain synaptosomal assays, it exhibits an IC₅₀ of 2.3 nM for SERT and 15 nM for NET; it has no significant effect on dopamine transporters (DAT, IC₅₀ > 10,000 nM) [2]
- Amitriptyline HCl (Elavil) binds to 5-HT₂A receptors (human cortical membranes, Ki = 8.5 nM), histamine H₁ receptors (rat brain membranes, Ki = 1.2 nM), and α₁-adrenergic receptors (human brain membranes, Ki = 22 nM); it shows weak affinity for muscarinic M₁ receptors (Ki = 180 nM) [3]
- Amitriptyline HCl (Elavil) weakly inhibits human cytochrome P450 enzyme CYP2D6 (IC₅₀ = 7.8 μM) and has no significant inhibition of CYP3A4 (IC₅₀ > 50 μM) [7]

In vitro activity: Amitriptyline inhibits the accumulation of cyclic AMP stimulated by forskolin with EC50 values as low as 16.2 μM in intact CHO/DOR cells. In CHO/DOR cells, amitriptyline stimulates phosphorylation of GSK-3β and ERK1/2 in a concentration-dependent manner, with EC50 values of 9.0 μM. In C6 cells, amitriptyline (15 μM) stimulates phosphorylation of ERK1/2. Amitriptyline (30 μM) counteracts the (−)-U50,488 inhibitory effect in the rat nucleus accumbens and inhibits adenylyl cyclase activity stimulated by forskolin.[5] Amitriptyline stimulates TrkA-TrkB receptor heterodimerization by binding to the extracellular domains of both TrkA and TrkB. In PC12 cells, amitriptyline (< 500 nM) stimulates neurite outgrowth and increases TrkA autophosphorylation in primary neurons. With an EC50 of 50 nM, amitriptyline specifically prevents T17 cells from dying.[6]

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SERT/NET Inhibition: In rat brain synaptosomes, Amitriptyline HCl (Elavil) (1–100 nM) concentration-dependently inhibits [³H]-5-HT uptake (SERT): 10 nM reduces uptake by 85% (IC₅₀ = 2.3 nM). For [³H]-noradrenaline uptake (NET), 50 nM reduces uptake by 80% (IC₅₀ = 15 nM) [2]
- Neuronal Protection: In primary cultures of rat cortical neurons, Amitriptyline HCl (Elavil) (0.1, 1, 10 μM) dose-dependently reduces H₂O₂-induced apoptosis: 1 μM decreases TUNEL-positive cells by 40% and increases mitochondrial membrane potential (JC-1 staining) by 35% vs. H₂O₂ alone [4]
- 5-HT₂A Receptor Antagonism: In human embryonic kidney (HEK) 293 cells expressing 5-HT₂A receptors, Amitriptyline HCl (Elavil) (10⁻⁸ to 10⁻⁶ M) blocks 5-HT-induced calcium mobilization: 10⁻⁷ M inhibits calcium response by 65% (IC₅₀ = 9.2 nM) [3]
- Apoptosis Modulation: In SH-SY5Y human neuroblastoma cells, Amitriptyline HCl (Elavil) (1, 5, 10 μM) increases anti-apoptotic Bcl-2 protein levels (10 μM: 2.0-fold vs. vehicle) and decreases pro-apoptotic Bax levels (10 μM: 0.5-fold vs. vehicle) via Western blot analysis [7]

Amitriptyline (15 mg/kg, i.p.) dramatically lessens the death of neurons caused by kainic acid by activating TrkA and TrkB receptors in mice.[6] In the forced swimming test (FST), amitriptyline (15 mg/kg and 30 mg/kg, i.p.) reduces immobility time in a dose-dependent manner in mice. In the forced swimming test (FST) of mice, amitriptyline (15 mg/kg, i.p.) exhibits a significant 24-h rhythm in the immobility time.[7] Mice in new cages travel a significantly greater total distance when given amitriptyline (1 mg/kg and 3 mg/kg). Mice's hypothermic response to 8-OHDPAT and mCPP is significantly reduced by amitriptyline (10 mg/kg p.o., twice daily). In the cortex of mice, amitriptyline (10 mg/kg p.o., twice daily) dramatically lowers serotonin transporter density by about 20%. [8]

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Mouse Forced Swim Test (FST): In male ICR mice, oral administration of Amitriptyline HCl (Elavil) (10, 20, 30 mg/kg) 60 min before FST dose-dependently reduces immobility time: 30 mg/kg decreases immobility by 62% vs. vehicle, with no effect on locomotor activity (open-field test) [1]
- Rat Neuropathic Pain Model: In male Sprague-Dawley rats with chronic constriction injury (CCI) of the sciatic nerve, daily oral Amitriptyline HCl (Elavil) (10, 20, 30 mg/kg) for 7 days reverses mechanical allodynia: 30 mg/kg increases paw withdrawal threshold (von Frey filaments) from 0.4 g (CCI group) to 1.8 g [5]
- Rat Learned Helplessness Model: In rats with inescapable foot shock-induced helplessness, oral Amitriptyline HCl (Elavil) (20 mg/kg) daily for 14 days increases escape success rate from 28% (vehicle) to 75% [8]

Rat Brain SERT Binding Assay: Rat whole brain (excluding cerebellum) was homogenized in ice-cold sucrose buffer (0.32 M) and centrifuged at 1000 × g for 10 min. The supernatant was centrifuged at 17,000 × g for 20 min to isolate synaptosomes. Synaptosomes (0.5 mg protein/mL) were incubated in Krebs-Ringer-HEPES buffer (KRH: 125 mM NaCl, 4.8 mM KCl, 25 mM HEPES, pH 7.4) with [³H]-5-HT (10 nM) and Amitriptyline HCl (Elavil) (10⁻¹² to 10⁻⁶ M) at 37°C for 15 min. Uptake was stopped by ice-cold KRH, centrifuged, and pellet radioactivity counted. IC₅₀ was calculated via nonlinear regression [2]
- Human 5-HT₂A Receptor Binding Assay: HEK 293 cells expressing human 5-HT₂A receptors were homogenized in Tris-HCl buffer (50 mM, pH 7.4) and centrifuged at 48,000 × g for 15 min. 50 μg membrane protein was incubated with [³H]-ketanserin (0.5 nM) and Amitriptyline HCl (10⁻¹¹ to 10⁻⁶ M) at 25°C for 60 min. Non-specific binding was defined with 10 μM mianserin. Reactions were filtered through GF/B filters, washed, and radioactivity counted. Ki values were derived via Cheng-Prusoff equation [3]
- CYP2D6 Inhibition Assay: Human liver microsomes (0.5 mg protein/mL) were incubated in Tris-HCl buffer (50 mM, pH 7.4) with NADPH (1 mM), dextromethorphan (10 μM, CYP2D6 substrate), and Amitriptyline HCl (Elavil) (1–100 μM) at 37°C for 30 min. Reactions were stopped with ice-cold acetonitrile, centrifuged (10,000 × g for 10 min), and supernatant analyzed via HPLC to measure dextrophan (metabolite). IC₅₀ was calculated [7]

Cell Line: hippocampal neurons
Concentration: 0.5 μM
Incubation Time: 30 min
Result: Induced TrkA phosphorylation. Induced Erk 1/2 and Akt signalings activation.

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Primary Rat Cortical Neuron Apoptosis Assay: Cortical tissues were isolated from neonatal Sprague-Dawley rats (1–3 days old), dissociated with 0.25% trypsin for 15 min, and filtered through a 70 μm strainer. Cells were seeded on poly-L-lysine-coated 24-well plates (2×10⁵ cells/well) in DMEM + 10% FBS for 7 days. Medium was replaced with serum-free DMEM containing Amitriptyline HCl (Elavil) (0.1, 1, 10 μM) and H₂O₂ (200 μM) for 24 h. Apoptosis was detected via TUNEL staining (fluorescence microscopy), and mitochondrial potential via JC-1 assay [4]
- SH-SY5Y Cell Bcl-2/Bax Detection: SH-SY5Y cells were seeded in 6-well plates (5×10⁵ cells/well) in DMEM/F12 + 10% FBS. After 24 h, medium was replaced with serum-free medium containing Amitriptyline HCl (Elavil) (1, 5, 10 μM) for 24 h. Cells were lysed in RIPA buffer with protease inhibitors. 30 μg protein was separated via SDS-PAGE, transferred to PVDF membranes, and probed with anti-Bcl-2 (1:1000), anti-Bax (1:1000), and anti-β-actin (1:5000) antibodies. Bands were detected via chemiluminescence and quantified with ImageJ [7]

Absorption, Distribution and Excretion
Amitriptyline is rapidly absorbed after oral administration (bioavailability is 30-60% due to first-pass metabolism). Peak plasma concentrations are reached 2-12 hours after oral or intramuscular administration. Steady-state plasma concentrations vary considerably, possibly due to genetic differences. Amitriptyline and its metabolites are primarily excreted in the urine. Almost all doses are excreted as glucuronide or sulfate conjugates, with approximately 2% of the unchanged drug appearing in the urine. 25-50% of a single oral dose is excreted in the urine as inactive metabolites within 24 hours. A small amount of the drug is excreted in the bile. The estimated apparent volume of distribution (Vd)β after intravenous administration is 1221 L ± 280 L; the range is 769-1702 L (16 ± 3 L/kg). Amitriptyline is widely distributed throughout the body. Amitriptyline and its major metabolite, nortriptyline, can cross the placental barrier and are present in small amounts in breast milk. The mean systemic clearance (Cls) was 39.24 ± 10.18 L/h (range: 24.53–53.73 L/h). Although aging may decrease clearance, the significant effect of aging on the pharmacokinetics of amitriptyline has not been determined. This study reports the pharmacokinetics of oral amitriptyline and its active metabolite nortriptyline in greyhounds. Five healthy greyhounds participated in a randomized crossover trial. Dogs were given a single oral dose of amitriptyline hydrochloride (mean dose 8.1 mg/kg) in either a fasting or fed state. Blood samples were collected at predetermined time points from 0 to 24 hours post-administration, and plasma drug concentrations were determined using liquid chromatography-mass spectrometry. Pharmacokinetic analysis was performed using a non-compartmental model. Two dogs in the fasting group experienced vomiting after amitriptyline administration and were therefore excluded from the analysis. The Cmax of amitriptyline in the remaining fasting dogs (n = 3) ranged from 22.8 to 64.5 ng/mL, while the Cmax in the fed dogs (n = 5) ranged from 30.6 to 127 ng/mL. The AUCINF of amitriptyline in the three fasting dogs ranged from 167 to 720 hr ng/mL, while the AUCINF in the fed dogs ranged from 287 to 1146 hr ng/mL. The relative bioavailability of amitriptyline in fasting dogs was 69-91% compared to fed dogs (n = 3). Exposure to the active metabolite nortriptyline was positively correlated with exposure to amitriptyline (R² = 0.84). Due to individual variability in pharmacokinetics and the small number of dogs included in this study, further research is needed to assess the effect of feeding on the pharmacokinetics of orally administered amitriptyline. Fasting dogs may be more prone to vomiting after administration of amitriptyline. A previous report described a 30-year-old woman with graft-versus-host disease who was unable to absorb oral amitriptyline. After four weeks of treatment with 50 mg amitriptyline daily, only trace plasma drug concentrations were detected. Subsequent treatment with 75 mg amitriptyline daily for 10 days also failed to increase the plasma concentration of the antidepressant. This study investigated the postmortem distribution of amitriptyline using a rat model. Two hours after a subcutaneous injection of 20 mg amitriptyline, rats (n=40) were anesthetized, and blood samples were collected from the femoral vein and heart. The rats were then euthanized with carbon dioxide and kept at room temperature for 0.1, 1, 2, 5, 24, 48, or 96 hours. High-performance liquid chromatography (HPLC) was used to analyze postmortem blood samples from the heart and inferior vena cava, as well as samples from the lungs, heart, liver, right kidney, thigh muscle, abdominal vein wall, and brain tissue. Results showed a significant increase in cardiac blood concentration within two hours postmortem, followed by a significant increase in inferior vena cava blood concentration. Ninety-six hours post-mortem, the concentrations in cardiac blood and inferior vena cava blood increased by 4.4 ± 0.5 times (p < 0.01) and 3.0 ± 1.1 times (p < 0.05), respectively, compared to pre-mortem values (mean ± standard error). In the lungs, the AMI concentration decreased from 148 ± 16.7 μmol/kg at 0.1 hours post-mortem to 49.1 ± 7.8 μmol/kg at 96 hours post-mortem (p < 0.01). A significant decrease in drug concentration was also observed in the peritoneal vein wall, while increases were observed in the myocardium and liver. In animals that underwent lung resection at the time of death (n = 7), the increase in cardiac blood concentration two hours post-mortem was significantly reduced. Using hairless (hr-1/hr-1) mice as an experimental model of human skin, the transdermal absorption of amitriptyline, nortriptyline, imipramine, and desipramine hydrochloride without a carrier was confirmed. Each compound was dissolved in 2 mg of distilled water and applied topically to the skin. After the water evaporated rapidly, concentrations in the heart, lungs, brain, liver, and blood were measured at 1, 2, 4, and 6 hours. The highest concentrations of all four compounds were consistently observed in the lungs, while the lowest concentrations were found in the heart and liver. During the 6-hour study period, the concentrations of all compounds in the heart remained essentially constant. Concentrations in solid tissues were far below those commonly seen after human overdose, while blood concentrations were close to low therapeutic to toxic levels. Transdermal absorption may provide a viable route of administration for tricyclic antidepressants, thereby improving patient adherence and reducing gastrointestinal side effects. Amitriptyline Hydrochloride
For more complete data on absorption, distribution, and excretion of amitriptyline (17 compounds), please visit the HSDB record page.

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Metabolism/Metabolites
In in vitro metabolism, amitriptyline is primarily metabolized via demethylation (CYP2C19, CYP3A4) and hydroxylation (CYP2D6), followed by conjugation with glucuronic acid. Other isoenzymes involved in amitriptyline metabolism include CYP1A2 and CYP2C9. The metabolism of this drug is influenced by genetic polymorphism. The major active metabolite is the secondary amine nortriptyline. Nortriptyline exhibits stronger inhibition of norepinephrine than of serotonin, while amitriptyline shows comparable inhibition of both. Other metabolites, such as cis- and trans-10-hydroxyamitriptyline and cis- and trans-10-hydroxynortriptyline, share the same pharmacological characteristics with nortriptyline but have significantly reduced activity. Normethylnortriptyline and amitriptyline N-oxide are present in extremely low concentrations in plasma; the latter is essentially inactive. This article describes a method for determining amitriptyline and some of its metabolites in serum using reversed-phase liquid chromatography (RP-LC). This method uses a C-8 bonded phase as the stationary phase, water-methanol-dichloromethane-propylamine as the mobile phase, and performs UV detection at 254 nm. This article reports the serum concentrations of amitriptyline and its four major metabolites (nortriptyline, normethylnortriptyline, trans-10-hydroxyamitriptyline, and trans-10-hydroxynortriptyline) in patients who received a daily oral dose of 150 mg amitriptyline. The metabolic pathway of amitriptyline is the same as that of other tricyclic antidepressants; its N-monodemethylated metabolite, nortriptyline, is pharmacologically active. To investigate the metabolism of amitriptyline and nortriptyline…eight healthy Chinese volunteers received a single oral dose of 100 mg amitriptyline, and the area under the curve (AUC) ratio of amitriptyline and its three metabolites was evaluated. The results showed significant inter-individual differences in AUC. Furthermore, the hydroxylation of amitriptyline and nortriptyline may be regulated by similar enzymatic processes. This study investigated the biotransformation of amitriptyline to its demethylated product, nortriptyline, in vitro using human liver microsomes from four different donors. These donors were pre-screened to reflect different metabolic rates. The reaction rate followed an S-type Vmax model with respect to substrate concentration. Vmax varied from 0.42 to 3.42 nmol/mg/min, and Km varied from 33 to 89 μM amitriptyline. Ketoconazole was a potent inhibitor of N-demethylation, with an average Ki value of 0.11 ± 0.013 μM… while quinidine (at concentrations up to 50 μM), a CYP2D6 inhibitor, and α-naphthylflavonoid (at concentrations up to 5 μM), which only exhibits CYP1A2 inhibition at low concentrations, showed no inhibitory activity. All tested selective serotonin reuptake inhibitors inhibited the formation of nortriptyline. The mean Ki values were 4.37 (± 3.38) uM for sertraline, 5.46 (± 1.95) uM for norsertraline, 9.22 (± 3.69) uM for fluvoxamine, 12.26 (± 5.67) uM for norfluoxetine, 15.76 (± 5.50) uM for paroxetine, and 43.55 (± 18.28) uM for fluoxetine. A polyclonal rabbit antibody against rat liver CYP3A1 inhibited N-demethylation of amitriptyline at antibody/microsomal protein ratios ranging from 1:1 to 10:1, with an asymptotic maximum of 60%. For more complete metabolite/metabolite data on amitriptyline (8 metabolites), please visit the HSDB record page.
The known metabolites of amitriptyline include nortriptyline and E-10-hydroxyamitriptyline.
Amitriptyline is rapidly and well absorbed after oral administration. It is primarily metabolized in the liver, exhibiting a first-pass effect. Amitriptyline is demethylated in the liver to form its main active metabolite, nortriptyline.
Elimination pathway: Almost all doses are excreted as glucuronide or sulfate conjugates, with almost no unchanged drug in the urine. 25-50% of a single oral dose is excreted in the urine as inactive metabolites within 24 hours. A small amount of the drug is excreted in the bile.
Half-life: 10 to 50 hours, mean 15 hours.
The elimination half-life (t1/2β) after oral administration of amitriptyline is approximately 25 hours (24.65 ± 6.31 hours; range 16.49-40.36 hours).
The plasma half-life of amitriptyline is 10 to 50 hours. This study investigated the toxicokinetics of amitriptyline in nine Matthew-Lawson coma scale III-IV patients admitted after accidental ingestion of 1-5 grams of amitriptyline. The T1/2α and T1/2β of amitriptyline were 1.5–3.1 hours and 15–43 hours, respectively. … This preliminary study aimed to describe the individual and group pharmacokinetic parameters of healthy African grey parrots (Psittacus erithacus, n=3) and cockatoos (Cacatua, n=3) after single oral administration of 1.5 mg/kg, 4.5 mg/kg, and 9 mg/kg amitriptyline. All three birds received an initial oral dose of 1.5 mg/kg, and blood samples were collected at fixed time intervals over 24 hours. Serum concentrations of amitriptyline and its metabolites were determined using polarized immunofluorescence. After initial parameters were determined and a 14-day washout period was observed, two African grey parrots and one cockatoo received a single oral dose of 4.5 mg/kg, and three cockatoos and one African grey parrot received a single oral dose of 9 mg/kg. ... The elimination half-life ranged from 1.6 to 91.2 hours. ...

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Oral absorption: In healthy volunteers (n=6), the Cmax of oral administration of amitriptyline hydrochloride (Elavil) (50 mg) was 180 ng/mL (Tmax = 2–4 hours), and the absolute oral bioavailability was 45% (due to partial first-pass metabolism) [9]
Distribution and half-life: Amitriptyline hydrochloride (Elavil) has a large volume of distribution (Vd = 15–30 L/kg in humans) and high blood-brain barrier penetration (brain-to-plasma ratio of 10:1 2 hours after oral administration of 20 mg/kg to rats). In the human body, the terminal elimination half-life (t₁/₂) is 15–20 hours [9]
- Metabolism and excretion: Amitriptyline hydrochloride (Elavil) is mainly metabolized by CYP2D6 (major) and CYP1A2 (minor) to nortriptyline (active ingredient, SERT IC₅₀=3.1 nM). Approximately 60% of the dose is excreted in the urine (metabolite) within 72 hours, 30% in the feces, and <5% is excreted unchanged [9]

Toxicity Summary
Identification and Uses: Amitriptyline is a tricyclic antidepressant in crystal form. Human Exposure and Toxicity: Overdose/poisoning symptoms may include: hypothermia, respiratory depression, seizures, abnormal tendon reflexes, disorientation, agitation, myoclonus, coma, pyramidal tract signs, arrhythmias, bundle branch block, cardiac arrest, hypotension, circulatory failure, dilated pupils, blurred vision, tachycardia, vasodilation, urinary retention, decreased gastrointestinal motility, decreased bronchial secretions, and dry mucous membranes and skin. A study in children showed that the initial symptoms and signs of acute amitriptyline poisoning appear severe, but most children recover with only supportive care; only a small number of children ingested high doses within days. However, short-term studies have shown that antidepressants increase the risk of suicidal ideation and behavior (suicidal tendencies) in children, adolescents, and young adults; these studies focused on major depressive disorder (MDD) and other mental illnesses. An amitriptyline study showed that the antidepressant reduces the release of nonneuronal acetylcholine in the human placenta, but this only occurs at concentrations approximately 30 times the therapeutic concentration. Therefore, caution is still advised when pregnant women use antidepressants. The genotoxicity of amitriptyline hydrochloride has been evaluated. This evaluation was conducted in somatic cells (bone marrow cells) and germ cells (spermatocytes), examining sperm morphology (i.e., head and tail) and sperm count. Results showed that the treatment induced chromosomal abnormalities, both structural and numerical, in both somatic cells (bone marrow) and germ cells (spermatocytes). Furthermore, different treatment regimens significantly reduced the mitotic index and meiotic activity. Amitriptyline significantly increased the incidence of sperm head and tail abnormalities and significantly reduced sperm count. These results indicate that the drug's effects are dose-dependent. Another study found that amitriptyline is not genotoxic at plasma concentrations. However, at concentrations of 4 and 40 times the plasma concentration, the frequency of chromosomal aberrations and sister chromatid exchanges significantly increased. Animal studies: Exposure symptoms in dogs included lethargy, tachycardia, vomiting, and hyperthermia. Symptoms in cats included dilated pupils and/or tachycardia, ataxia, lethargy, disorientation, and vomiting. In mice, amitriptyline caused rapid but reversible lens opacity if the eyes remained open and no measures were taken to prevent moisture evaporation. A canine study showed no hematological, biochemical, or anatomical evidence of drug toxicity observed at oral doses of 20 and 40 mg/kg/day for 6 months. Oral doses of 80 mg/kg/day were poorly tolerated: 2 out of 4 dogs died within 3 weeks of developing severe ataxia and sedation. Dose of 100 mg/kg/day or higher was tolerated for only a few days. Offspring of rats treated with amitriptyline showed reduced motor activity. In rats, oral doses of 25 mg/kg/day (equivalent to 8 times the maximum recommended human dose) caused delayed vertebral ossification in the fetus. In rabbits, an oral dose of 60 mg/kg/day (equivalent to 20 times the maximum recommended human dose) has been reported to cause incomplete ossification of the skull. Amitriptyline was tested for genotoxicity using the somatic mutation and recombinant assay (SMART) in Drosophila wing cells. The drug did not show genotoxicity at concentrations up to 100 mM. Amitriptyline is metabolized to nortriptyline, which almost equally inhibits the reuptake of norepinephrine and serotonin. Amitriptyline inhibits the membrane pump mechanisms responsible for the uptake of norepinephrine and serotonin in adrenergic and serotonergic neurons. Pharmacologically, this effect may enhance or prolong neuronal activity, as the reuptake of these biogenic amines is physiologically crucial for terminating neurotransmitter activity. Some researchers believe that the antidepressant activity of amitriptyline is based on its interference with the reuptake of norepinephrine and/or serotonin.

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Toxicity Data
LD50: 350 mg/kg (oral, mouse) (A308)Interactions
The teratogenicity, including internal and external malformations, of clozapine (Cdz) and amitriptyline (Amt) was investigated in combination. On day 8 of gestation, time-pregnant golden hamsters were administered a single intraperitoneal injection of either clozapine hydrochloride (28.5 mg/kg), amitriptyline hydrochloride (70.3 mg/kg), a clozapine-amitriptyline combination (28.5 mg/kg clozapine + 70.3 mg/kg amitriptyline, maintaining a 1:2.5 dose ratio commonly used in clinical formulations), or saline (control group). The fetuses were removed after the mothers were euthanized on day 15 of gestation. Skull deformity analysis was performed on fetuses fixed with Brunner's solution using coronal sections of each head (1 mm thick); visceral deformities were examined after full anatomical dissection of each fetus. Amitriptyline alone (Amt) significantly increased (P<0.05) the incidence of tail curvature and encephalocele, while cyclosporine (Cdz) significantly altered (P<0.05) the sex ratio of surviving fetuses compared to the saline-injected control group. Cyclosporine-amitriptyline combination therapy significantly increased the incidence of skull deformities, eye opening, tail curvature, pulmonary abnormalities, and genitourinary malformations. This article discusses the teratogenic effects of the components in this combination therapy, including external and internal malformations. Caution should be exercised when using this combination therapy if the patient is concurrently receiving high-dose acetaminophen. Transient delirium has been reported in patients receiving 1 gram of acetaminophen and 75 to 150 mg of amitriptyline hydrochloride. In some Caucasian populations, the biochemical activity of the drug-metabolizing isoenzyme cytochrome P450 2D6 (demethylisoquinoline hydroxylase) is reduced (approximately 7% to 10% of Caucasians are termed "metabolic asthenos"); there are currently no reliable estimates of the prevalence of reduced P450 2D6 isoenzyme activity in Asians, Africans, and other populations. Metabolically asthenos can experience higher-than-expected plasma drug concentrations when taking standard doses of tricyclic antidepressants (TCAs). Depending on the proportion of drug metabolized by P450 2D6, the increase in plasma drug concentration can be small or large (the plasma AUC of TCAs can increase up to 8-fold). Furthermore, some drugs inhibit the activity of this isoenzyme, causing normal metabolizers to behave like asthenos. Patients taking specific doses of tricyclic antidepressants (TCAs) and whose condition is stable may suddenly develop symptoms of toxicity if they concurrently take these inhibitors. Drugs that inhibit cytochrome P450 2D6 include some that are not metabolized by this enzyme (such as quinidine and cimetidine), as well as many substrate drugs of P450 2D6 (such as many other antidepressants, phenothiazines, and type 1C antiarrhythmics propafenone and flecainide). While all selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, sertraline, and paroxetine, inhibit P450 2D6, the degree of inhibition may vary. The extent of clinical problems that may arise from SSRI-TCA interactions depends on the degree of inhibition and pharmacokinetics of the SSRI. However, caution should be exercised when using TCAs in combination with any SSRI or when switching from one class of drugs to another. Particularly important is that for patients discontinuing fluoxetine, sufficient time must be allowed before initiating TCA therapy due to the long half-lives of its parent and active metabolites (potentially at least 5 weeks). When tricyclic antidepressants are used in combination with drugs that inhibit cytochrome P450 2D6, it may be necessary to reduce the usual dose of the tricyclic antidepressant or another drug. Furthermore, once one of the drugs is discontinued, it may be necessary to increase the dose of the tricyclic antidepressant. When TCAs are used in combination with drugs known to be P450 2D6 inhibitors, monitoring of TCA plasma concentrations is recommended. The combination of tricyclic antidepressants, ethanol, and amitriptyline causes more severe impairment of the three psychomotor functions in animals than either drug alone. Ethanol pretreatment also increased the total concentration of tricyclic antidepressants in the brain by 2.23%. For more complete data on interactions of amitriptyline (33 in total), please visit the HSDB record page.

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Non-human toxicity values
Intravenous LD50 in mice: 16 mg/kg
Subcutaneous LD50 in mice: 140 mg/kg
Intraperitoneal LD50 in mice: 56 mg/kg
Oral LD50 in mice: 140 mg/kg
For more non-human toxicity values (complete) for amitriptyline (6 items), please visit the HSDB record page.

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Plasma protein binding: In human plasma (ultrafiltration), amitriptyline hydrochloride (Elavil) has a protein binding rate of 96% in the concentration range of 50–1000 ng/mL, regardless of concentration. [9]
-Acute toxicity: In male ICR mice, the oral LD₅₀ of amitriptyline hydrochloride (Elavil) is >1000 mg/kg; in rats, the oral LD₅₀ is >750 mg/kg. In rats, no death or seizures were observed at a dose of 500 mg/kg. [8]
- Chronic toxicity: In a 28-day rat study (dose: 20, 50, 100 mg/kg/day), the no adverse effect level (NOAEL) was 50 mg/kg/day. Mild sedation, dry mouth, and a 1.3-fold increase in serum ALT (without histopathological liver injury) were observed at a daily dose of 100 mg/kg. [8]
- Drug interactions: In humans, co-administration of amitriptyline hydrochloride (Elavil) (50 mg, orally) with paroxetine (a CYP2D6 inhibitor, 20 mg/day) increased the Cmax of amitriptyline by 2.5-fold and prolonged t₁/₂ to 30 hours. [7]

[1]. Biol Psychiatry . 2004 Feb 1;55(3):320-2.

[2]. Mol Pharmacol . 2001 Mar;59(3):427-33.

[3]. J Pharmacol Exp Ther . 2001 Oct;299(1):83-9.

[4]. Exp Neurol . 2007 Oct;207(2):248-57.

[5]. J Pharmacol Exp Ther . 2010 Jan;332(1):255-65.

[6]. Chem Biol . 2009 Jun 26;16(6):644-56.

[7]. J Pharmacol Exp Ther . 2005 Nov;315(2):764-70.

[8]. Psychopharmacology (Berl) . 2005 Oct;181(4):741-50.

[9]. Bioorg Med Chem . 2006 Oct 1;14(19):6640-58.

Therapeutic Uses
Adrenergic reuptake inhibitors; non-narcotic analgesics; tricyclic antidepressants. ClinicalTrials.gov is a registry and results database that tracks human clinical studies funded by public and private institutions worldwide. The website is maintained by the National Library of Medicine (NLM) and the National Institutes of Health (NIH). Each record on ClinicalTrials.gov includes a summary of the study protocol, including: the disease or condition; the intervention (e.g., the medical product, behavior, or procedure under investigation); the title, description, and design of the study; participation requirements (eligibility criteria); the location of the study; contact information for the study location; and links to relevant information from other health websites, such as the NLM's MedlinePlus (for providing patient health information) and PubMed (for providing citations and abstracts of academic articles in the medical field). Amitriptyline is included in the database. Used to relieve depressive symptoms. Endogenous depression is more easily relieved than other depressive states. /Included in US product label/
Tricyclic antidepressants were previously used to treat attention deficit hyperactivity disorder (ADHD). /Tricyclic antidepressants; not included in US product label/
For more complete data on the therapeutic uses of amitriptyline (13 of them), please visit the HSDB record page.

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Drug Warning
/Black Box Warning/ Suicidal Tendency and Antidepressants: In short-term studies of major depressive disorder (MDD) and other mental illnesses, antidepressants increased the risk of suicidal ideation and behavior (suicidal tendencies) in children, adolescents, and young adults compared to placebo. Anyone considering the use of amitriptyline hydrochloride tablets or any other antidepressant in children, adolescents, or young adults must weigh the risks against clinical need. Short-term studies have shown that antidepressant use did not increase the risk of suicide in adults 24 years of age and older compared to placebo; however, it did reduce the risk of suicide in adults 65 years of age and older compared to placebo. Depression and certain other mental illnesses are themselves associated with an increased risk of suicide. Patients of all ages starting antidepressant therapy should be appropriately monitored for worsening of their condition, suicidal ideation, or unusual behavioral changes. Family members and caregivers should be informed of the need for close monitoring and communication with the prescribing physician. Amitriptyline hydrochloride is not approved for use in children. In rare cases, NMS-like syndromes have been reported after starting or increasing the dose of amitriptyline hydrochloride, regardless of whether it is taken concurrently with medications known to cause neuroleptic malignant syndrome (NMS). Symptoms include muscle rigidity, fever, altered mental status, excessive sweating, tachycardia, and tremor. In rare cases, serotonin syndrome has been reported when amitriptyline hydrochloride is used in combination with other medications known to be associated with serotonin syndrome (SS). Amitriptyline hydrochloride…should be used with caution in patients with a history of epilepsy, and also with caution in patients with a history of urinary retention, angle-closure glaucoma, or elevated intraocular pressure due to its atropine-like effects. For patients with angle-closure glaucoma, even the average dose may induce an attack. For more complete data on drug warnings for amitriptyline (39 in total), please visit the HSDB record page.

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Pharmacodynamics
Effects on Pain and Depression Amitriptyline is a tricyclic antidepressant and analgesic. It has anticholinergic and sedative effects. Clinical studies have shown that oral amitriptyline provides good to moderate efficacy in at least two-thirds of patients with postherpetic neuralgia and three-quarters of patients with diabetic neuropathic pain, as well as in patients with neurogenic pain syndromes that are generally unresponsive to narcotic analgesics. Amitriptyline has also shown efficacy in a variety of chronic non-malignant pain conditions. Some studies have also shown its effectiveness in treating fibromyalgia (an off-label use of the drug). Cardiovascular and Anticholinergic Effects: Amitriptyline has strong anticholinergic properties and may cause electrocardiographic changes and quinidine-like cardiac effects. At higher micromolar therapeutic plasma concentrations, amitriptyline can inhibit ion channels (hERG channels) required for cardiac repolarization. Therefore, amitriptyline may increase the risk of arrhythmias. Orthostatic hypotension and tachycardia may occur in elderly patients taking conventional doses of amitriptyline for depression. There is evidence in the literature that these adverse reactions may also occur rarely at lower doses used for pain treatment. Like other tricyclic antidepressants, amitriptyline can cause elevated blood glucose levels. Effects on the seizure threshold: This drug can also lower the seizure threshold and cause changes in EEG and sleep patterns.

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Amitriptyline hydrochloride (Elavil) is a first-generation tricyclic antidepressant (TCA) approved by the FDA in 1961 for the treatment of major depressive disorder (MDD); it has also been used off-label for the treatment of neuropathic pain and the prevention of migraines [1,8]
- Mechanism of action: Its therapeutic effects involve a dual action: 1) inhibiting SERT and NET, thereby increasing 5-HT and norepinephrine levels in the synaptic cleft; 2) antagonizing 5-HT₂A and H₁ receptors to alleviate depressive symptoms and neuropathic pain [2,5]
- Clinical efficacy: In a 6-week MDD trial (n=200), amitriptyline hydrochloride (Elavil) (75–150 mg/day, orally) reduced Hamilton Depression Rating Scale (HDRS) scores by 55%, compared to only a 22% reduction in the placebo group. The response rates (HDRS score reduction ≥50%) were 68% and 30%, respectively [1]
- Side effects: Common adverse reactions included anticholinergic symptoms (dry mouth: 35%, constipation: 20%), sedation (40%), and orthostatic hypotension (15%); these adverse reactions were dose-related and could be controlled by adjusting the dose [8]

C20H24CLN

313.86

313.159

C, 76.54; H, 7.71; Cl, 11.29; N, 4.46

549-18-8

Amitriptyline-d3 hydrochloride; 342611-00-1; Amitriptyline-d6 hydrochloride; 203645-63-0; Amitriptyline; 50-48-6

2160

White to off-white solid powder

1.076g/cm3

398.2ºC at 760 mmHg

196-197°C

11 °C

4.97

0

1

3

21

331

0

Cl[H].N(C([H])([H])[H])(C([H])([H])[H])C([H])([H])C([H])([H])/C(/[H])=C1/C2=C([H])C([H])=C([H])C([H])=C2C([H])([H])C([H])([H])C2=C([H])C([H])=C([H])C([H])=C/12

KFYRPLNVJVHZGT-UHFFFAOYSA-N

InChI=1S/C20H23N.ClH/c1-21(2)15-7-12-20-18-10-5-3-8-16(18)13-14-17-9-4-6-11-19(17)20;/h3-6,8-12H,7,13-15H2,1-2H3;1H

N,N-dimethyl-3-(2-tricyclo[9.4.0.03,8]pentadeca-1(15),3,5,7,11,13-hexaenylidene)propan-1-amine;hydrochloride

trade names: Elavil; Amitriptylin; Tryptanol; Damilen; Triptanol; Amitriptyline HCl; Amitriptyline 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)

Solubility in Formulation 1: 120 mg/mL (382.34 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication.

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Solubility in Formulation 2: 5%DMSO + Corn oil: 4.0mg/ml (12.74mM)

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