Beneficial adjunctive effects of the 5HT3 receptor antagonist ondansetron on symptoms, function and cognition in early phase schizophrenia in a double-blind, 2 × 2 factorial design, randomised controlled comparison with simvastatin.

Background: Variable benefits have been reported from the adjunctive use of simvastatin and the 5HT3 receptor antagonist, ondansetron, in patients with schizophrenia. We investigated their independent efficacy and possible synergy to improve negative symptoms of schizophrenia within a single trial.

Methods: A 6-month, randomised, double-blind, placebo-controlled trial with a 4-arm, 2 × 2 factorial design, in three centres in Pakistan. In total, 303 people with stable treated schizophrenia aged 18-65 were randomly allocated to add-on ondansetron, simvastatin, both or neither. The primary outcome was a Positive and Negative Syndrome Scale (PANSS) negative score at 3 and 6 months.

Results: Mixed model analysis and analysis of covariance revealed no main effects of simvastatin or ondansetron but a significant negative interaction between them (p = 0.03); when given alone, both drugs significantly reduced negative symptoms compared to placebo but they were ineffective in combination. Individual treatment effects versus placebo were -1.9 points (95%CIs -3.23, -0.49; p = 0.01) for simvastatin and -1.6 points for ondansetron (95%CIs -3.00, -0.14; p = 0.03). Combined treatment significantly increased depression and side effects. In those with less than the median 5 years of treatment, ondansetron improved all PANSS subscales, global functioning measures and verbal learning and fluency, whereas simvastatin did not.

Conclusion: Small improvement in negative symptoms on simvastatin and ondansetron individually are not synergistic in combination in treating negative symptoms of schizophrenia. Ondansetron showed broad efficacy in patients on stable antipsychotic treatment within 5 years of illness. The findings suggest that ondansetron should be evaluated in patients at risk of psychosis or early in treatment.