Carbamazepine reduces olanzapine by what percentage range?

• A. 10%
• B. 50%
• C. 80%
• D. 36-71%

Answer: (D)

This question tests how enzyme induction by carbamazepine affects the metabolism of another drug. Carbamazepine is a strong inducer of hepatic enzymes, especially CYP3A4, so it speeds up the breakdown of drugs processed by these enzymes. Olanzapine is metabolized in the liver and, when carbamazepine is present, its clearance increases significantly, leading to much lower plasma levels. In practice, the observed reduction in olanzapine exposure when given with carbamazepine is variable but typically falls in the range of about 36% to 71% (roughly one-third to two-thirds lower). Because this drop can reduce antipsychotic effect, clinicians often need to adjust the olanzapine dose or consider an alternative medication, with careful monitoring for symptom change.