Drug utilization review of risperidone for outpatients in a tertiary referral hospital in Singapore

BACKGROUND: Risperidone has been used in Singapore for schizophrenia since 1996. However, little information is available on its utilization pattern. OBJECTIVE: To examine the risperidone utilization pattern in the Psychiatric Outpatient Clinic of the National University Hospital. METHOD: Medical records of all outpatients with schizophrenia prescribed with risperidone from 1 September1999 to 31 August 2000 were reviewed. RESULTS: A total of 417 risperidone prescriptions were dispensed for 130 outpatients (50 male, 80 female) during the study period. The mean +/- SD daily doses for prescriptions and for patients were 2.3 +/- 1.3 mg and 2.1 +/- 1.1 mg, respectively. Among these patients, 28 (21.5%) received at least one concomitant conventional antipsychotic and 71 (54.6%) received a concomitant anti-Parkinsonian agent. Logistic regression analysis suggested that a higher risperidone dose was associated with the greater probability of anti-Parkinsonian agent usage. CONCLUSIONS: The mean risperidone dose during the study period was towards the lower end of recommendation for schizophrenia. Further study is warranted to confirm and explain the pattern of low-dose risperidone, and the high use of concomitant conventional antipsychotics and anti-Parkinsonian agents in Singapore. Elucidation of these would provide a valuable insight for the management of Asian patients with schizophrenia using risperidone. However, the current data indicate that the practice of using a lower dose of risperidone could represent better affordability and an improved cost-effectiveness ratio of risperidone compared with conventional antipsychotics in Asian patients.