A placebo-controlled study of tropisetron added to risperidone for the treatment of negative symptoms in chronic and stable schizophrenia

A growing body of evidence illustrates that 5-HT3 receptor antagonist drugs may be of benefit in the treatment of negative symptoms in schizophrenia. The objective of this study was to assess the efficacy and tolerability of tropisetron add-on to risperidone on negative symptoms in patients with chronic stable schizophrenia. In a double-blind, placebo-controlled 8-week trial, 40 patients with chronic schizophrenia who were stabilized on risperidone were randomized into tropisetron or placebo add-on groups. Psychotic symptoms were measured using the Positive and Negative Syndrome Scale (PANSS) every 2 weeks. Furthermore, extrapyramidal and depressive symptoms as well as side effects were assessed. The primary outcome measure was the difference in change from baseline of negative subscale scores between the two groups at week 8. Tropisetron resulted in greater improvement of the total PANSS scores [F(1.860,70.699) = 37.366, p < 0.001] as well as negative scores [F(2.439,92.675) = 16.623, p < 0.001] and general psychopathology [F(1.767,67.158) = 4.602, p = 0.017], but not positive subscale scores [F(1.348, 51.218) = 0.048, p = 0.893] compared to placebo. In a multiple regression analysis controlling for positive, extrapyramidal, and depressive symptoms, treatment group (standardized beta = -0.640) significantly predicted changes in primary negative symptoms. The side effect profile did not differ significantly between the two groups. Tropisetron add-on to risperidone improves the primary negative symptoms of patients with chronic stable schizophrenia.