DOI: 10.36347/sajp

Pages: 58-61

Risperidone (R) is a new generation atypical antipsychotic used for schizophrenia-treatment. Today, most effective method for CYP2D6 enzyme phenotyping is dextromethorphan metabolism. The aim of this study is to compare risperidone plasma level with dextromethorphan metabolite ratio in Turkish psychiatric patients receiving risperidone monotherapy and to investigate whether 9-hydroxyrisperidone ratio could be a phenotype marker for CYP2D6 enzyme. The study included 41 patients receiving R monotherapy in Üsküdar University NP Istanbul Hospital between March 2011 and February 2012. On the 7th day of risperidone,risperidone plasma sample and CYP2D6 enzyme phenotyping was worked. Phenotyping was performed in the urine according to dextromethorphan metabolite ratio. If that ratio is less than 0.003 ultra-rapid metabolizer, 0.003-0.3 and intermediate metabolizer/ normal metabolizer; more than 0.3 phenotyping was calculated as poor metabolizer. Plasma Risperidone / 9-OH risperidone ratio is ≥ 1: poor metabolizer (PM); less than 0.1 ulta rapid metabolizer (UM), values between 0.2-0.9 were evaluated as intermediate- or normal metabolizer(IM/NM). In 92.9% (n:39) of the cases, phenotype was consistent with risperidone blood levels. In 4.8% (n:2) CYP2D6 enzyme phenotype was not consistent with risperidone /9-hydroxyrisperidone. The strong relationship between dextromethorphan metabolite ratio in urine and risperidone hydroxylation. As monitoring of the plasma levels of risperidone is more practical, Therapeutic Drug Monitoring(TDM), as a phenotype marker in predicting CYP2D6 enzyme phenotype on patients using risperidone, can be used as an important data in monitoring the treatment.