The time required to attain the maximum plasma level of risperidone (RIS) is shorter for RIS oral solution (OS) than for RIS standard tablets (ST), although both forms have equal bioavailability. The objective of this study was to clarify whether RIS-OS shows a faster onset of efficacy and lower adverse events than RIS-ST. The two forms of risperidone were compared with respect to effectiveness including a speed of response, efficacy and tolerability. An open-label, 24-week, multicentre, randomized, flexible-dose study comparing the RIS-OS (mean dose, 3.7 mg; N=44) to the RIS-ST (mean dose, 3.7 mg; N=37) in acutely ill patients with schizophrenia showed no differences. Outcome measures included psychopathology, tolerability (extrapyramidal symptoms and serum prolactin), and Drug Attitude Inventory. This study was conducted between October 2006 and October 2008. Both RIS-OS- and RIS-ST-treated patients showed statistically significant reductions from the baseline in the mean scores of the Positive and Negative Syndrome Scale (PANSS)-total and PANSS-excite component, with no statistically significant differences between the treatment groups. The accumulated treatment response ratio was similar between the two groups. There was no significant difference in the Drug-Induced Extrapyramidal Symptom Scale score or serum prolactin increase between the treatment groups, but RIS-OS appeared to induce less serum prolactin increase than RIS-ST in drug-naïve female patients. Because there is no theoretical reason why this should be so, these results will require confirmation from a double-blind study in a larger sample. No significant difference was observed in the subjective drug attitude between the two groups. The original hypothesis that RIS-OS shows an earlier onset of efficacy or less adverse events than RIS-ST was not supported in this study. Subsequent studies should carefully establish the differences among various forms of antipsychotic drugs.
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