Risperidone is an antipsychotic used as the first-line treatment of schizophrenia. Risperidone is metabolised by enzyme CYP2D6. Activity of this enzyme can be predicted by genotypization.

To explore the possibility of different response rate to risperidone in first-episode schizophrenia patients with different CYP2D6 genotype.

To asses the utility of CYP2D6 pharmacogenetic testing in patients with schizophrenia treated with risperidone.

CYP2D6 genotype was assessed in 22 first-episode schizophrenic patients by use of automatic sequencing of DNA isolated from peripheral leukocytes. PANSS score was assessed every week of treatment until the change in medication or patient release.

Response was defined as at least 30% reduction in total PANSS. Differences in response rate between groups were tested by Fisher's exact test.

10 CYP2D6 extensive metabolisers (EM), 8 intermediate metabolisers (IM) and 4 poor metabolisers (PM) were identified. Criteria for response met 4 EM, 4 IM and 1 PM. Differences in response rate between groups were not statistically significant.

Although group of IM had higher response rate than EM and PM, differences in response rate did not reach statistical significance. Further differences may be found by extending the sample size. An useful approach would be also to examine differences in occurrence of adverse effects and subjective tolerance of the treatment.

The study was supported by the grant of Czech Ministry of Health No. NS 9676-4/2008.