CYP2D6 metabolizes risperidone into 9-hydroxi-risperidone, as well as other drugs. CYP2D6 shows genetic polymorphism, and 6-8% of Caucasians are “slow metabolizers”. “Fast metabolizers” show lower plasma levels of risperidone and higher levels of 9-hydroxi-risperidone than “slow metabolizers”. The aim of this study is to collect information about the hypothetical relationship between metabolism phenotype and parameters related to sanitary resources utilization in patients treated with risperidone.

Plasma levels of risperidone and 9-hydroxi-risperidone were determined in 52 patients treated at the Acute Unit setting, to establish their metabolism phenotype. Patients were grouped as fast (n=11), slow (n=13) or intermediate metabolizers (n=28), according to risperidone/9-hydroxi-risperidone ratio logarithm and using eighty and twenty percentiles as cut-points. Hospitalizations, emergency services utilization and visits to community mental health center during two years were recorded in the three groups.

Fast metabolizers showed a higher mean number of visits to community mental health centers (35.7 vs 24.8, fast and slow metabolizers respectively, p=0.667), a higher mean number of hospitalizations (2.45 vs 1.3, fast and slow metabolizers respectively; p=0.091), a longer mean length of hospitalizations (57.3 vs 47.6 days, fast and slow metabolizers respectively; p=0.581) and a higher number of visits to emergency services (2.45 vs 1, fast and slow metabolizers respectively; p=0.01), although differences only reached statistical significance in this last parameter.

In spite of methodological limitations (mainly the small sample size), the present study shows some preliminary evidence about the influence of pharmacogenetic factors on the evolution of psychotic patients treated with risperidone.