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Atypical antipsychotic (treatment-resistant schizophrenia)

Clozapine

Brand names: Clozaril, Denzapine, Zaponex

Clozapine is an atypical antipsychotic used for treatment-resistant schizophrenia, where it can be uniquely effective; its use requires registration with a monitoring service.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Recommended starting oral dosage is 12.5 mg once daily or twice daily. ( 2.2 ) If well-tolerated, increase the total daily dosage in increments of 25 mg to 50 mg per day at target dosage of 150 mg to 225 mg twice per day by the end of two weeks. ( 2.2 ) Subsequently may increase the doage in increments up to 100 mg, once or twice weekly. ( 2.2 ) Maximum daily dosage is 450 mg twice daily. ( 2.2 ) Administer with or without food. Clozapine ODT may be allowed to disintegrate or chewed, and may be taken with or without water. See additional administration instructions in the full prescribing information. ( 2.2 ) See dosage modification based on ANC results. ( 2.3 , 2.4 ) See recommendations …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-03-13. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It antagonises multiple receptors (including dopamine D2 and serotonin 5-HT2) with a distinctive receptor profile.

Prescribing in practice

  • Agranulocytosis is a defining risk — mandatory regular full-blood-count monitoring through a patient-monitoring scheme, and immediate review/stop for neutropenia or signs of infection.
  • Myocarditis and cardiomyopathy (especially in the first weeks), severe constipation/ileus (which can be fatal), seizures, sedation, hypersalivation and metabolic effects all occur.
  • Smoking affects clozapine levels (stopping smoking can raise them); after any break of more than 48 hours it must be re-titrated from a low dose.

Monitoring

Mandatory scheduled FBC monitoring; monitor for myocarditis (early), bowel function (constipation), seizures, weight, glucose and lipids, and levels where relevant.

Counselling the patient

  • You must have your regular blood tests — the medicine cannot be supplied without them.
  • Report fever, sore throat or feeling unwell, chest pain or breathlessness, and any difficulty opening your bowels.
  • Tell your team if you change your smoking, and never miss doses for more than a day or two without advice.

Evidence & guidelines

The most effective option for treatment-resistant schizophrenia (NICE NG178), used within a strict monitoring framework.

Reference: NICE CG178; Clozapine CPMS SPC; Maudsley Prescribing Guidelines 14th ed.; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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