AMITRIPTYLINE HYDROCHLORIDE
Clinical safety rating: caution
Animal studies have proved adverse effects but may be safe for humans
Inhibits reuptake of serotonin and norepinephrine, leading to increased concentrations at synaptic cleft; also blocks histamine H1, alpha-1 adrenergic, and muscarinic cholinergic receptors.
| Metabolism | Primarily hepatic via CYP2D6, CYP3A4, CYP1A2, and CYP2C19; active metabolite nortriptyline; undergoes demethylation, hydroxylation, and conjugation. |
| Excretion | Primarily renal (approximately 30-50% as unchanged drug and metabolites, mainly glucuronide conjugates and hydroxylated metabolites). Fecal excretion accounts for <5%. Enterohepatic recirculation may occur. |
| Half-life | Terminal elimination half-life is 15-35 hours (range 9-46 hours); clinical context: steady-state concentrations achieved within 7-10 days; may be prolonged in elderly, hepatic impairment, or CYP2D6 poor metabolizers. |
| Protein binding | Approximately 94-96%; primarily bound to alpha-1-acid glycoprotein (AAG), with minor binding to albumin and lipoproteins. |
| Volume of Distribution | 10-20 L/kg (large Vd due to extensive tissue binding); clinical meaning: high tissue penetration, especially CNS, and slow redistribution from tissues. |
| Bioavailability | Oral: 30-60% due to extensive first-pass metabolism (CYP2C19, CYP3A4, CYP2D6); significant interindividual variability. |
| Onset of Action | Oral: Antidepressant effect 1-3 weeks; anxiolytic/sedative effects: within hours to days. IM: Not available. IV: Not approved. Topical: Not standard. |
| Duration of Action | Oral: Half-life supports once-daily dosing; antidepressant effects persist for weeks after discontinuation due to adaptive changes; analgesic effects may last 4-6 hours for neuropathic pain. |
Oral: 25-150 mg daily in divided doses or as a single bedtime dose; maximum 300 mg/day.
| Dosage form | TABLET |
| Renal impairment | GFR 10-50 mL/min: use 50% of normal dose; GFR <10 mL/min: use 25% of normal dose. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use. |
| Pediatric use | Adolescents: 10-50 mg daily in divided doses; children under 12 years (for enuresis): 6-10 years: 10-20 mg, 11+ years: 25-50 mg at bedtime. |
| Geriatric use | Start at 10-25 mg at bedtime; increase by 10-25 mg every 3-7 days as tolerated; maximum 75-100 mg daily; monitor for CNS and anticholinergic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
MAOIs can cause serotonin syndrome and hyperpyrexia Strong anticholinergic effects may occur with other drugs like benztropine Increased risk of suicide in children and young adults.
| Breastfeeding | Amitriptyline and its metabolite nortriptyline are excreted in breast milk with an M/P ratio of approximately 1.0 for amitriptyline. Infant daily dose is about 1-2% of maternal weight-adjusted dose. No adverse effects reported in most infants; however, monitor for drowsiness, poor feeding. American Academy of Pediatrics considers amitriptyline compatible with breastfeeding. |
| Teratogenic Risk | First trimester: Limited data suggest a small increased risk of congenital malformations, particularly cardiovascular defects. Second trimester: No specific malformation risk, but possible effects on fetal growth. Third trimester: Risk of neonatal withdrawal syndrome (irritability, feeding difficulties) and anticholinergic effects (constipation, urinary retention). Overall risk is low; benefits may outweigh risks in severe depression. |
■ FDA Black Box Warning
Increased risk of suicidal thinking and behavior in children, adolescents, and young adults taking antidepressants. Close monitoring for clinical worsening, suicidality, or unusual changes in behavior is recommended.
| Common Effects | neuropathic pain |
| Serious Effects |
Concurrent use with MAOIs (risk of serotonin syndrome), recent myocardial infarction, hypersensitivity to tricyclic antidepressants, during acute recovery phase of MI, use with cisapride or other QT-prolonging drugs.
| Precautions | Cardiotoxicity (QT prolongation, arrhythmias), serotonin syndrome, activation of mania/hypomania, angle-closure glaucoma, urinary retention, seizures, increased intraocular pressure, orthostatic hypotension, drowsiness, withdrawal symptoms upon abrupt discontinuation. |
| Food/Dietary |
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| Fetal Monitoring | Maternal monitoring includes serum drug levels if toxicity suspected, ECG for cardiac arrhythmias, and close observation for anticholinergic side effects. Fetal monitoring includes ultrasound for growth and anatomy if first-trimester exposure, and neonatal assessment for withdrawal symptoms post-delivery. |
| Fertility Effects | Amitriptyline may cause hyperprolactinemia via dopamine blockade, potentially leading to galactorrhea, menstrual irregularities, and impaired fertility. Effects are generally reversible upon discontinuation. Animal studies show no significant impact on fertility at therapeutic doses. |
| Avoid alcohol and tyramine-rich foods (e.g., aged cheese, cured meats, soy sauce) due to risk of hypertensive crisis. Limit caffeine intake; may increase CNS stimulation. Grapefruit juice may increase plasma levels; avoid or limit consumption. |
| Clinical Pearls | Do not discontinue abruptly; taper over 2-4 weeks to prevent withdrawal symptoms. Use with caution in patients with cardiac conduction defects (prolongs QTc interval). Serum levels >500 ng/mL are associated with toxicity. Start at 10-25 mg at bedtime for neuropathic pain. May precipitate mania in bipolar disorder. |
| Patient Advice | Take at bedtime to minimize daytime sedation. · Avoid alcohol and other CNS depressants. · Report symptoms of urinary retention, vision changes, or rapid heartbeat. · May cause dry mouth; use sugar-free gum or candy. · Avoid abrupt discontinuation; follow your doctor's tapering plan. · Notify your doctor if you experience suicidal thoughts or worsening depression. |