Little Effects of Low Dosage of Levomepromazine on Plasma Risperidone Levels

In the present study, we investigated the effects of levomepromazine on plasma risperidone concentrations in a steady state. Twenty patients taking risperidone at a stable dose for more than 2 weeks who were considered to require levomepromazine coadministration were selected. The scores of excitement in BPRS significantly decreased 2 weeks after the coadministration of levomepromazine. Plasma risperidone concentrations and the ratio of risperidone and 9-hydroxyrisperidone (risperidone/9-hydroxyrisperidone) did not change between before and 2 weeks after the coadministration of levomepromazine. The extrapyramidal symptoms were not worsened by the coadministration of levomepromazine. These results suggest that a low dosage of levomepromazine, use as a sedative adjuvant to risperidone treatment, have no statistically significant effect on the trough plasma concentrations of risperidone.

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