12. Pharmacokinetic Drug-Drug Interactions: Antipsychotics and Mood Stabilizers
Key Points
Antipsychotics
- Cigarrette smoking and CYP1A2:
- Patients who smoke may need a higher dosage of clozapine and olanzapine.
- Smoking cessation in patients taking FGAs has been associated with emergence of extrapyramidal side effects, due to decreased metabolism.
- Ziprasidone and paliperidone have the least potential for drug-drug interactions via the CYP450 system.
- Carbamazepine can significantly decrease the levels of oral contraceptives below a reliably effective level.
- Recommendation: women of childbearing potential should use other contraceptive methods.
- Lamotrigine and valproate are metabolized by glucuronidation. Valproate can double lamotrigine levels by inhibiting its metabolism.
- Recommendation: cut the lamotrigine dose in half when prescribing valproate.
- Lamotrigine can decrease quetiapine concentrations.
- Lithium levels can be increased by NSAIDs, diuretics (especially thiazides) and Angiotensing Converting Enzyme Inhibitors (ACEIs).
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