Association of Concomitant Amlodipine Use With Serum Olanzapine Concentrations and Clinical Outcomes in Patients With Schizophrenia.

objectiveTo examine whether concomitant amlodipine use was associated with steady-state serum olanzapine concentration and clinical outcomes in patients with schizophrenia.

methodsThis retrospective study included 45 inpatients with schizophrenia and hypertension who received olanzapine 10 mg/day plus amlodipine 5 mg/day (experimental group) and 52 inpatients who received olanzapine 10 mg/day alone (control group). PANSS and SDSS scores were assessed at baseline and week 7, and recorded adverse events were evaluated at week 9.

resultsMean serum olanzapine concentration was lower in the combination group than in the olanzapine-alone group (40.56 ± 18.86 vs. 50.23 ± 23.41 ng/mL; unadjusted p = 0.027; age-adjusted p = 0.032) (Figure 1). Improvements in positive symptoms, negative symptoms, and SDSS scores were smaller in the combination group, whereas PANSS total and general psychopathology changes did not differ. Serum olanzapine concentration was not significantly correlated with any PANSS or SDSS change. Recorded adverse-event rates did not differ significantly.

conclusionsConcomitant amlodipine use was associated with lower serum olanzapine concentration and smaller improvements in selected clinical domains. The individual-level analyses did not establish a concentration-response relationship, and the retrospective design precludes causal inference. Haemodynamic safety could not be evaluated because complete standardised blood-pressure data were unavailable. These findings suggest that closer monitoring of clinical response and serum olanzapine concentrations may be considered when amlodipine is co-prescribed, particularly in patients with suboptimal treatment response.