Clozapine is a second-generation (atypical) antipsychotic medication, considered the gold standard for treatment-resistant schizophrenia. It is a dibenzodiazepine derivative with a unique receptor binding profile, offering superior efficacy for positive and negative symptoms but carrying a significant risk of severe adverse effects, most notably agranulocytosis, necessitating strict hematological monitoring.
Adult: **Initial:** 12.5 mg (half of 25mg tablet) once or twice daily on Day 1, increased cautiously by 25-50 mg/day to a target range of 300-450 mg/day by end of week 2. **Therapeutic:** 200-600 mg/day in divided doses. Maximum daily dose should generally not exceed 900 mg. Dose must be titrated slowly to minimize hypotension and sedation.
Note: Administer with or without food. To minimize orthostatic hypotension, advise taking at bedtime, especially during initial titration. The tablet can be split. Consistent timing of doses is important. Do not stop abruptly due to risk of rebound psychosis and cholinergic rebound.
Clozapine's exact antipsychotic mechanism is complex and not fully understood. It demonstrates a broad receptor binding profile with higher affinity for serotonin (5-HT2A) receptors than dopamine (D2) receptors. This atypical profile is thought to contribute to its efficacy in treatment-resistant cases and lower incidence of extrapyramidal symptoms (EPS).
Pregnancy: **Category B (US FDA).** Limited human data. Use only if potential benefit justifies potential fetal risk. Neonates exposed in the 3rd trimester are at risk for extrapyramidal symptoms and withdrawal. A risk-benefit discussion with a psychiatrist and obstetrician is mandatory.
Driving: **Not advisable,** especially during dose titration. Can cause significant drowsiness, dizziness, blurred vision, and syncope, impairing the ability to drive or operate machinery.
| Carbamazepine, Phenytoin, Phenobarbital | Induce CYP1A2/3A4, significantly decreasing clozapine plasma levels, increasing risk of treatment failure AND concurrent bone marrow suppression risk with carbamazepine. | Major - Contraindicated/Requires alternative |
| Fluoroquinolones (Ciprofloxacin), Fluvoxamine | Potent CYP1A2 inhibitors, significantly increasing clozapine plasma levels, leading to toxicity (seizures, sedation, myocarditis risk). | Major |
| Erythromycin, Clarithromycin, Ketoconazole, Itraconazole | CYP3A4 inhibitors, increase clozapine levels. | Moderate |
| Rifampicin | Potent CYP inducer, decreases clozapine levels substantially. | Major |
| Selective Serotonin Reuptake Inhibitors (SSRIs) like Fluoxetine, Paroxetine | CYP2D6 inhibitors, moderate increase in clozapine levels. | Moderate |
| Benzodiazepines, Opioids, Alcohol, other CNS Depressants | Potentiate CNS and respiratory depression, profound sedation. | Major |
| Anticholinergic drugs (e.g., Trihexyphenidyl) | Potentiate anticholinergic side effects (ileus, delirium, hyperthermia). | Moderate |
| Antihypertensives | Enhanced hypotensive effect. | Moderate |
| Lithium | Increased risk of seizures, NMS, encephalopathy. | Moderate |