Clozapine — NZ Medication Guide
📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.
What is Clozapine?
Clozapine is a second-generation antipsychotic reserved for treatment-resistant schizophrenia due to its serious side effect profile but unique efficacy. This medication is funded by Pharmac for treatment-resistant schizophrenia; mandatory monitoring programme required.
What is Clozapine Used For?
Indicated for treatment-resistant schizophrenia (inadequate response to at least two antipsychotics) and reducing suicidal behaviour in schizophrenia. The only antipsychotic proven effective in this population.
How Does Clozapine Work?
Broad receptor profile — blocks dopamine D1/D2/D4, serotonin 5-HT2A/2C, histamine H1, muscarinic, and adrenergic receptors. Low D2 affinity and high 5-HT2A affinity explain fewer extrapyramidal effects but superior efficacy.
How to Take Clozapine
Start at 12.5–25 mg/night and titrate very slowly over 2–4 weeks. Doses range from 150–600 mg/day. Mandatory blood count monitoring throughout. Must be prescribed via the NZ Clozapine National Monitoring Service (NZCNS).
Common Side Effects of Clozapine
- Hypersalivation (drooling — often severe)
- Weight gain (significant)
- Sedation
- Constipation (risk of fatal paralytic ileus — proactive management required)
- Tachycardia
- Dizziness on standing
- Metabolic syndrome
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Agranulocytosis (1–2% risk — mandatory weekly blood monitoring)
- Myocarditis/cardiomyopathy (first 4–8 weeks — cardiac monitoring required)
- Seizures (dose-related)
- Paralytic ileus (from severe constipation — potentially fatal)
- Neuroleptic malignant syndrome
- Pulmonary embolism (increased risk)
Drug Interactions
Clozapine may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:
- Fluvoxamine (markedly increases clozapine levels — avoid)
- Ciprofloxacin (increases levels)
- Carbamazepine (avoid — seizure and agranulocytosis risk)
- Smoking cessation (stopping smoking significantly increases clozapine levels — dose adjustment needed)
New Zealand Prescribing Information
Clozapine (Clopine® 25 mg, 100 mg, 200 mg) is dispensed only through pharmacies enrolled in the NZ Clozapine National Monitoring Service (NZCNS). Mandatory FBC monitoring: weekly for 18 weeks, fortnightly for 1 year, then monthly if stable. ANC below 1.5 x 10⁹/L requires immediate suspension.
Frequently Asked Questions
Why do I need weekly blood tests for clozapine?
Clozapine causes agranulocytosis in 1–2% of patients, depleting infection-fighting white blood cells. Weekly monitoring detects this early, allowing prompt cessation before life-threatening infection occurs. Frequency reduces over time with stable counts.
What if I miss a dose of clozapine?
Missing more than 48 hours requires urgent contact with your psychiatrist. Restarting after a break must be re-titrated from the beginning — restarting at a previously tolerated dose can cause dangerous hypotension or cardiac arrest.
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: