Clomipramine

Indications

• FDA-approved for obsessive-compulsive disorder in adults and in children and adolescents 10 years of age and older.
• Remains the efficacy benchmark in OCD meta-analyses, though selective serotonin reuptake inhibitors are preferred first line for tolerability.
• Off-label for depression in the United States, where it is approved as an antidepressant in many other countries but not by the FDA.
• Off-label for panic disorder, where controlled trials show efficacy at doses lower than those needed for obsessive-compulsive symptoms.
• Off-label for trichotillomania, body dysmorphic disorder, premature ejaculation, and cataplexy associated with narcolepsy.
• Reasonable next step after two failed adequate SSRI trials in OCD, either alone or combined with exposure and response prevention.

Mechanism of action

• The most potent serotonin reuptake inhibitor among tricyclics, with roughly tenfold greater affinity for the serotonin than norepinephrine transporter.
• Its major metabolite desmethylclomipramine is a strong norepinephrine reuptake inhibitor, so the drug is effectively dual-acting at steady state.
• Strong serotonergic tone in cortico-striato-thalamo-cortical circuits is the presumed basis of antiobsessional efficacy in OCD.
• Substantial muscarinic, histaminic, and alpha-1 blockade produces the anticholinergic effects, sedation, and orthostasis typical of the class.
• Dose-dependent lowering of seizure threshold is greater than for other tricyclics and is the main constraint on the maximum dose.

Pharmacokinetics

• Well absorbed orally, with bioavailability near 50 percent after extensive first-pass metabolism; take with food to reduce nausea.
• Parent drug half-life is about 32 hours while desmethylclomipramine averages roughly 69 hours, so steady state takes 1 to 2 weeks.
• Demethylation is mediated by CYP1A2, CYP3A4, and CYP2C19, and hydroxylation of both parent and metabolite proceeds through CYP2D6.
• CYP2D6 poor metabolizers and patients on strong 2D6 inhibitors accumulate drug substantially, warranting dose reduction and level checks.
• Highly protein bound with a large volume of distribution; renal excretion of conjugated metabolites accounts for most elimination.

Dosing

• Start 25 mg PO daily with food and titrate over the first 2 weeks toward 100 mg/day in divided doses as tolerated.
• Adult maximum is 250 mg/day; after titration the total dose may be consolidated at bedtime to limit daytime sedation.
• In children and adolescents 10 years and older the maximum is 3 mg/kg/day or 200 mg/day, whichever amount is smaller.
• Supplied as 25, 50, and 75 mg capsules; adequate OCD trials require at least 10 to 12 weeks at the maximum tolerated dose.
• Reduce the dose in hepatic impairment and titrate slowly in renal impairment, since hydroxylated metabolites accumulate.
• Taper gradually over several weeks when stopping to avoid nausea, headache, malaise, insomnia, and cholinergic rebound symptoms.

Adverse effects

• Dry mouth affects roughly 84 percent, constipation about 47 percent, and somnolence about 54 percent of patients in registration trials.
• Sexual dysfunction is very common, with ejaculatory failure reported in about 42 percent of treated men in clinical trials.
• Seizures occur in approximately 0.5 percent at doses up to 250 mg/day and rise steeply above that, making the ceiling a hard limit.
• Weight gain, tremor, sweating, and orthostatic dizziness are frequent and often drive discontinuation during long-term therapy.
• Cardiac conduction slowing with PR, QRS, and QT prolongation occurs at higher doses and dominates the picture in overdose.
• Rare serious events include hepatitis, agranulocytosis, syndrome of inappropriate antidiuretic hormone, and neuroleptic malignant-like reactions.

Monitoring

• Obtain a baseline ECG in patients over 50 years, in any known cardiac disease, and before exceeding 200 mg/day in any adult.
• Plasma levels are not routinely required, but a combined clomipramine plus desmethylclomipramine level helps assess toxicity or nonresponse.
• Screen for seizure risk factors including head injury, alcohol withdrawal, and concurrent proconvulsant drugs before dose escalation.
• Track weight, blood pressure with orthostatics, and bowel function at each visit, and ask directly about sexual side effects.
• Use the Yale-Brown Obsessive Compulsive Scale at baseline and every 4 to 6 weeks to document response objectively.

Interactions

• Contraindicated with monoamine oxidase inhibitors and within 14 days of stopping one because of fatal serotonin syndrome risk.
• Strong CYP2D6 inhibitors including fluoxetine, paroxetine, and bupropion markedly raise levels and increase seizure and cardiac risk.
• CYP1A2 and CYP3A4 modulators matter: fluvoxamine and ketoconazole raise levels while carbamazepine and smoking lower them.
• Additive serotonergic burden with SSRIs, triptans, tramadol, and linezolid can precipitate serotonin syndrome even without an MAOI.
• Drugs that lower seizure threshold such as bupropion, tramadol, and high-dose antipsychotics compound the dose-dependent seizure risk.

Special populations

• Pregnancy data are limited; third-trimester exposure has been associated with neonatal jitteriness, tremor, and feeding difficulty.
• Present in breast milk at low relative infant dose; monitor the infant for sedation and poor feeding if used during lactation.
• Approved from age 10 years for OCD, with weight-based capping and close monitoring for suicidality and cardiac effects required.
• Beers Criteria list tricyclics as potentially inappropriate at age 65 and older; if used, start at 10-25 mg with slow titration.
• Lower doses are needed in hepatic impairment, and clearance of metabolites is reduced in significant chronic kidney disease.

Clinical pearls

• Adequate OCD trials need 10-12 weeks at the maximum tolerated dose before calling it a failure.
• Seizure risk is the ceiling: never exceed 250 mg/day in adults.
• Ejaculatory failure occurs in about 4 of 10 men; ask directly or adherence quietly fails.