CLOZARIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CLOZARIL (CLOZARIL).
Clozapine is an atypical antipsychotic that binds to multiple receptors including dopamine D1-D5 (with greater affinity for D4), serotonin 5-HT2A, 5-HT2C, 5-HT3, 5-HT6, 5-HT7, histamine H1, muscarinic M1-M5, and adrenergic α1- and α2-receptors. Its therapeutic efficacy is primarily attributed to antagonism of D2 and 5-HT2A receptors. It also has weak D2 antagonism and rapid dissociation from D2 receptors, which may contribute to lower extrapyramidal side effects.
| Metabolism | Metabolized primarily by cytochrome P450 isoenzymes 1A2 (CYP1A2), with minor contributions from CYP2D6, CYP3A4, and CYP2C9. Main metabolite is norclozapine (desmethylclozapine), which is active. |
| Excretion | Approximately 50% excreted renally as metabolites, with less than 1% unchanged; 30% eliminated in feces via biliary excretion. |
| Half-life | Terminal elimination half-life is approximately 8–12 hours at steady state; range 6–26 hours, increasing with dose due to saturable metabolism. |
| Protein binding | ~97% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd = 4–5 L/kg, indicating extensive tissue distribution and large peripheral compartment. |
| Bioavailability | Oral bioavailability is 50–60% due to first-pass metabolism. |
| Onset of Action | Oral: 2–3 days for initial sedation; antipsychotic effects may take 2–4 weeks to become clinically significant. |
| Duration of Action | Duration of action is 12–24 hours for acute effects; sustained antipsychotic benefit requires continuous dosing. |
| Molecular Weight | 326.82 |
Initial 12.5 mg orally once or twice daily, titrate by 25-50 mg/day over 2 weeks to target 300-450 mg/day in divided doses; max 900 mg/day.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment for GFR >10 mL/min; use caution and monitor for accumulation in severe impairment (GFR <10 mL/min) with consideration of reduced doses. |
| Liver impairment | Contraindicated in patients with prior clozapine-induced agranulocytosis or severe hepatic impairment (Child-Pugh C). In mild to moderate impairment (Child-Pugh A or B), use with caution and reduce dose to 50-66% of usual target. |
| Pediatric use | Not FDA-approved for children <18 years; off-label use: initial 12.5 mg/day, titrate slowly based on response and tolerability, typical target 200-400 mg/day in divided doses. |
| Geriatric use | Initiate at 12.5 mg once daily; titrate more slowly (25 mg increments per week); usual therapeutic range 100-300 mg/day; monitor for hypotension, sedation, and anticholinergic effects. |
| 1st trimester | Risk of congenital malformations based on limited human data; animal studies show reproductive toxicity. Use only if clearly needed and benefit outweighs risk. Consider registry enrollment. |
| 2nd trimester | Risk of maternal seizures, agranulocytosis, and metabolic complications. Can cause gestational diabetes, weight gain, and hypertension. Monitor closely. |
| 3rd trimester | Risk of neonatal extrapyramidal symptoms, withdrawal, and sedation after delivery. If possible, taper or switch to a lower-risk antipsychotic in late third trimester. Monitor neonate for adverse effects. |
Clinical note
Comprehensive clinical and safety monograph for CLOZARIL (CLOZARIL).
| Placental transfer | Clozapine crosses the placenta readily. Cord blood concentrations are about 1.5–3 times lower than maternal plasma. Extensive placental transfer with fetal exposure comparable to maternal. |
| Breastfeeding | Clozapine is excreted into breast milk in low to moderate amounts. Relative infant dose estimated at 0.3–2.1% of weight-adjusted maternal dose. Reported adverse effects include drowsiness, poor feeding, and agranulocytosis (rare). Monitor infant for sedation, poor suckling, and infection. Avoid breastfeeding if maternal dose >200 mg/day or infant has compromised immune function. Consider alternative therapy if feasible. |
■ FDA Black Box Warning
Severe neutropenia (absolute neutrophil count <500/μL) due to significant risk of fatal agranulocytosis, requiring mandatory baseline and regular monitoring of white blood cell counts before and during therapy. Myocarditis and cardiomyopathy, which can be fatal; discontinue if suspected.
| Serious Effects |
Myeloproliferative disordersHistory of clozapine-induced agranulocytosis or severe granulocytopeniaUncontrolled epilepsySevere central nervous system depressionComatose statesKnown hypersensitivity to clozapineHistory of paralytic ileus
| Precautions | Severe neutropenia/agranulocytosis; myocarditis and cardiomyopathy; seizures (dose-dependent); orthostatic hypotension with or without syncope; increased risk of falls; QT interval prolongation; eosinophilia; pulmonary embolism; tardive dyskinesia; metabolic changes (hyperglycemia, dyslipidemia, weight gain); anticholinergic toxicity; neuroleptic malignant syndrome; gastrointestinal hypomotility (severe constipation, ileus); fever; thrombocytopenia; liver injury; withdrawal reactions; interactions with other drugs that suppress bone marrow. |
| Food/Dietary |
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| Lactation Rating | L3 (Moderately Safe) - Limited data suggest risk of adverse effects, but generally low risk with monitoring. |
| Teratogenic Risk | Pregnancy category C. First trimester: Limited human data; animal studies show adverse effects (reduced fetal weight, delayed ossification) at doses 0.3-3 times the maximum human dose. Second/third trimester: Potential for extrapyramidal symptoms and/or withdrawal in neonates if exposed late (tremors, hypertonia, poor feeding). |
| Fetal Monitoring | Maternal: CBC (absolute neutrophil count) weekly for first 18 weeks, then every 2 weeks for 1 year, then monthly; monitor for orthostatic hypotension, sedation, agranulocytosis, seizures. Fetal/neonatal: Growth surveillance (ultrasound) and assessment for extrapyramidal symptoms after delivery. |
| Fertility Effects | In animal studies, no impairment of fertility at doses up to 0.5 times MRHD. In humans, hyperprolactinemia can occur, potentially causing menstrual irregularities, galactorrhea, and reduced libido; effect on fertility not systematically studied but may be reversible upon discontinuation. |
| Avoid grapefruit juice as it may increase clozapine levels. Limit caffeine consumption due to potential to raise clozapine concentrations. High-fat meals may slightly increase absorption; take consistently with respect to meals. Ensure adequate hydration and fiber intake to prevent constipation. No other specific dietary restrictions. |
| Clinical Pearls | Require regular absolute neutrophil count (ANC) monitoring due to risk of agranulocytosis. Titrate slowly to minimize orthostatic hypotension, sedation, and hypersalivation. Potent anticholinergic effects can cause constipation and ileus. May lower seizure threshold; dose-related risk especially >600 mg/day. Smoking induces CYP1A2, reducing clozapine levels; advise smoking cessation or dose adjustment. Cimetidine, caffeine, and oral contraceptives may increase levels. Discontinue if myocarditis or cardiomyopathy suspected. Monitor for eosinophilia, which may precede DRESS syndrome. Consider therapeutic drug monitoring for efficacy and toxicity (target trough: 350-600 ng/mL). |
| Patient Advice | Report immediately any signs of infection (fever, sore throat, lethargy) or unusual bruising/bleeding due to risk of agranulocytosis; weekly blood tests are mandatory for first 6 months, then biweekly. · Avoid driving or operating heavy machinery until you know how this medication affects you, as it may cause drowsiness, dizziness, and blurred vision. · Rise slowly from sitting or lying positions to prevent falls from orthostatic hypotension. · Do not stop taking this medication abruptly, as it can cause withdrawal symptoms and relapse of psychosis; taper under medical supervision. · Limit caffeine intake and avoid smoking without telling your doctor, as these can alter drug levels. · Report symptoms such as chest pain, palpitations, shortness of breath, or swelling of feet/ankles (possible myocarditis/cardiomyopathy). · Clozapine can cause increased salivation (especially at night); use a towel on pillow and maintain oral hygiene. |