CLOZAPINE
Clinical safety rating: safe
Animal studies have demonstrated safety
Atypical antipsychotic; binds to dopamine D4, serotonin 5-HT2A, and adrenergic α2 receptors; weak D2 antagonist with rapid dissociation; also affects histaminergic and cholinergic receptors.
| Metabolism | Primarily by CYP1A2, with minor contributions from CYP2D6, CYP3A4, and CYP2C19. |
| Excretion | Approximately 50% of the dose is excreted in urine (30% as unchanged drug and metabolites) and 30% in feces via biliary elimination. |
| Half-life | Terminal elimination half-life is 8 to 12 hours (steady-state), but can range from 4 to 66 hours; requires dose adjustment in renal/hepatic impairment. |
| Protein binding | 97% bound to plasma proteins (mainly albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | Vd is 1.6 to 5.0 L/kg (average 2-5 L/kg), indicating extensive tissue distribution. |
| Bioavailability | Oral: 50-60% due to first-pass metabolism. |
| Onset of Action | Oral: 1-2 weeks for antipsychotic effect; maximal effect may take several weeks to months. |
| Duration of Action | Due to long half-life, effects persist for 24-48 hours after single dose; steady-state achieved in 5-7 days. |
Initial: 12.5 mg orally once or twice daily; titrate gradually by 25-50 mg/day to target dose 300-450 mg/day in divided doses; max 900 mg/day.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment guidelines for renal impairment; use caution in severe impairment (GFR <30 mL/min) with slower titration and lower target doses. |
| Liver impairment | Child-Pugh class A: no adjustment; Child-Pugh class B: reduce dose by 50% and titrate slowly; Child-Pugh class C: contraindicated. |
| Pediatric use | Not FDA-approved for pediatric use; dosing off-label: initial 12.5 mg/day, titrate up to 25-50 mg/day increments; target 100-400 mg/day based on response; max 500 mg/day; weight-based: 0.15-0.5 mg/kg/day divided BID-TID, titrate to 3-6 mg/kg/day; max 9 mg/kg/day. |
| Geriatric use | Start at 12.5 mg once daily; titrate slowly by 12.5-25 mg increments; target 150-300 mg/day; monitor for orthostatic hypotension, sedation, and anticholinergic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Bone marrow suppressants may increase risk of agranulocytosis Can cause severe neutropenia and agranulocytosis requiring mandatory WBC monitoring.
| Breastfeeding | Clozapine is excreted into breast milk; reported M/P ratio is approximately 2.8. Due to high relative infant dose (estimated 1-2% maternal weight-adjusted dose) and risk of sedation and agranulocytosis, breastfeeding is generally not recommended. |
| Teratogenic Risk | Clozapine is not associated with major congenital malformations in first trimester exposure but may cause gestational diabetes, weight gain, and preterm birth. Third trimester exposure risks include neonatal withdrawal symptoms (agitation, hypertonia, tremors, sedation) and possible extrapyramidal signs. |
■ FDA Black Box Warning
Severe neutropenia/agranulocytosis; myocarditis and cardiomyopathy; seizures; orthostatic hypotension with syncope; increased mortality in elderly patients with dementia-related psychosis.
| Common Effects | Sedation |
| Serious Effects |
History of agranulocytosis or severe neutropenia; uncontrolled epilepsy; paralytic ileus; severe CNS depression or coma; concurrent use with other agents that suppress bone marrow; hypersensitivity to clozapine.
| Precautions | Monitor CBC weekly for 6 months, then biweekly for 6 months, then monthly; monitor for myocarditis; titrate slowly; avoid in patients with uncontrolled epilepsy; risk of metabolic syndrome; anticholinergic toxicity; eosinophilia; withdrawal reactions. |
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| Fetal Monitoring | Monitor maternal white blood cell count and absolute neutrophil count (ANC) weekly for first 18 weeks, then every 2 weeks up to 1 year, then monthly due to agranulocytosis risk. Assess for gestational diabetes, weight gain, and blood pressure. Fetal monitoring includes growth scans and fetal movement counts. Newborns should be monitored for withdrawal symptoms and extrapyramidal signs for 48-72 hours post-delivery. |
| Fertility Effects | Clozapine can elevate prolactin levels less than other antipsychotics but may still cause menstrual irregularities, galactorrhea, and impaired ovulation. Hyperprolactinemia may reduce fertility. Weight gain and metabolic changes can also contribute to infertility. |