Drug interactions
Clozapine + Isoniazid
Severity: Minor
Clozapine and Isoniazid: minor interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Isoniazid is a weak inhibitor of several CYP enzymes and may modestly raise clozapine exposure in some patients. Higher clozapine levels could increase sedation, hypotension, seizure risk and other dose-related adverse effects. The effect is generally small and variable.
What this interaction means in plain words
Clozapine and Isoniazid have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Clozapine belongs to Central Nervous System; Isoniazid belongs to Anti Bacterial.
Why it happens
Weak, variable inhibition of CYP-mediated clozapine metabolism (mainly CYP1A2/3A4) by isoniazid.
What to do
Monitor for sedation, orthostasis and seizures when starting or stopping isoniazid. Check a clozapine level if toxicity is suspected and adjust the dose accordingly.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Isoniazid
Other interactions of Clozapine
- Clozapine + Deferiprone Contraindicated
- Clozapine + Irinotecan Contraindicated
- Clozapine + Pimozide Contraindicated
- Clozapine + Thioridazine Contraindicated
- Acalabrutinib + Clozapine Major
- Adagrasib + Clozapine Major
Frequently asked questions
Can I take Clozapine with Isoniazid?
MediHelp rates the interaction as minor. Clozapine and Isoniazid have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Isoniazid is a weak inhibitor of several CYP enzymes and may modestly raise clozapine exposure in some patients. Higher clozapine levels could increase sedation, hypotension, seizure risk and other dose-related adverse effects. The effect is generally small and variable.
How serious is the interaction between Clozapine and Isoniazid?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for sedation, orthostasis and seizures when starting or stopping isoniazid. Check a clozapine level if toxicity is suspected and adjust the dose accordingly.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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