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 in refractory cases but carrying a significant risk of severe adverse effects, most notably agranulocytosis, necessitating strict hematological monitoring.
Adult: **Initial:** 12.5 mg once or twice daily, increased gradually by 25-50 mg/day to a target dose of 300-450 mg/day by end of week 2. **Therapeutic range:** 200-600 mg/day in divided doses. Some patients may require up to 900 mg/day. Dose titration must be slow to minimize hypotension, sedation, and seizures.
Note: Administer with or without food. Food may slow absorption and reduce peak concentration, potentially minimizing side effects. The total daily dose is usually divided into 2-3 doses. The evening dose can be larger to promote sleep and manage daytime sedation. Tablets should be swallowed whole with a full glass of water.
Clozapine's exact mechanism in schizophrenia is unknown but is believed to be mediated through a combination of antagonistic activity at dopamine type 2 (D2) and serotonin type 2A (5-HT2A) receptors, with a higher affinity for 5-HT2A receptors. This atypical profile is associated with a lower incidence of extrapyramidal symptoms (EPS). It also has affinity for adrenergic, cholinergic, and histaminergic receptors, contributing to both its therapeutic and side effect profile.
Pregnancy: **Pregnancy Category C (US FDA).** Data is limited. Use only if potential benefit justifies potential fetal risk. Neonates exposed in the 3rd trimester are at risk for extrapyramidal symptoms and withdrawal. Register with pregnancy registry if used.
Driving: **NOT ADVISABLE,** especially during dose titration. Can cause significant sedation, dizziness, and blurred vision, impairing alertness and motor skills.
| Carbamazepine | Induces CYP1A2/3A4, significantly reducing clozapine plasma levels by 50% or more. Also increases risk of agranulocytosis. CONTRAINDICATED. | High |
| Fluvoxamine, Ciprofloxacin | Potent CYP1A2 inhibitors, can increase clozapine levels 5-10 fold, leading to toxicity. | High |
| Smoking/Tobacco | Polycyclic hydrocarbons in smoke induce CYP1A2, reducing clozapine levels by ~30-50%. Smoking cessation can lead to a rapid rise in levels. | High |
| Benzodiazepines (e.g., Lorazepam, Clonazepam) | Increased risk of profound sedation, respiratory depression, and collapse, especially during initial titration. | High |
| Warfarin | Clozapine may potentiate anticoagulant effect; monitor INR closely. | Moderate |
| Lithium | May increase risk of seizures, NMS, and encephalopathy. Use with caution. | Moderate |
| Selective Serotonin Reuptake Inhibitors (SSRIs) like Fluoxetine, Paroxetine | CYP2D6 inhibition can increase clozapine levels. | Moderate |
| Anticholinergic drugs (e.g., Trihexyphenidyl) | Additive anticholinergic effects, increasing risk of constipation, urinary retention, and delirium. | Moderate |
Same composition (Clozapine (100mg)), different brands: