Which drug's plasma levels can be reduced by carbamazepine by up to 80%, potentially becoming undetectable?

Which drug's plasma levels can be reduced by carbamazepine by up to 80%, potentially becoming undetectable?

• A. Clozapine
• B. Olanzapine
• C. Quetiapine
• D. Risperidone

Answer: (B)

Carbamazepine is a strong inducer of hepatic enzymes, especially CYP3A4 and, to some extent, CYP1A2. Olanzapine is mainly cleared by these enzymes, so when carbamazepine is added, the metabolism of olanzapine speeds up substantially. This can drive olanzapine plasma levels down by a large margin—reported cases show reductions up to around 80%, and in some situations levels may become undetectable. Clinically, this means the antipsychotic effect of olanzapine can be lost when combined with carbamazepine, leading to symptom relapse. If this combination is necessary, clinicians often consider dose adjustment of olanzapine, switching to a different mood stabilizer with less inducing effect, or closely monitoring response and, if available, drug levels.

Carbamazepine is a strong inducer of hepatic enzymes, especially CYP3A4 and, to some extent, CYP1A2. Olanzapine is mainly cleared by these enzymes, so when carbamazepine is added, the metabolism of olanzapine speeds up substantially. This can drive olanzapine plasma levels down by a large margin—reported cases show reductions up to around 80%, and in some situations levels may become undetectable.

Clinically, this means the antipsychotic effect of olanzapine can be lost when combined with carbamazepine, leading to symptom relapse. If this combination is necessary, clinicians often consider dose adjustment of olanzapine, switching to a different mood stabilizer with less inducing effect, or closely monitoring response and, if available, drug levels.