Risperidone and Total 9-Hydroxyrisperidone in Relation to Prescribed Dose and Other Factors: Data From a Therapeutic Drug Monitoring Service, 2002-2010

Background: Information on the plasma risperidone and total 9-hydroxyrisperidone concentrations (‘total risperidone’) attained in clinical practice is scant. The aim of this work was to gather such information to better inform the interpretation of results.
Method: This involved the audit of plasma total risperidone data from a risperidone therapeutic drug monitoring service 2002–2010.
Results: There were 586 samples from 411 patients [289 (70%) males aged at the time of the first sample (median, range) 37 (7–83) years and 121 females aged 42 (10–91) years]. In patients aged 18 years and over, the mode of risperidone administration was oral: 242 samples (163 patients), risperidone long-acting injection (RLAI): 42 samples (39 patients), both oral and RLAI: 18 samples (12 patients), no information: 266 samples (211 patients). No risperidone/9-hydroxyrisperidone was detected in 10% of the samples, including 5 samples from patients prescribed RLAI. In the remainder, the mean (SD) total plasma total risperidone was all samples 35 (36), oral only 33 (29), RLAI only 23 (16), oral and RLAI 50 (21) µg/L. Overall, only 45% of the samples had plasma total risperidone within the range 20–59 mcg/L. Multiple linear regression analysis (95 samples) revealed that sex, smoking habit, and dose explained 21% of the variation in plasma total risperidone after oral dosage (dose alone only explained 11% of the variation). There was no discernable influence of age, body weight, and the plasma risperidone:total 9-hydroxyrisperidone ratio on plasma total risperidone.
Conclusions: Risperidone therapeutic drug monitoring can help assess adherence and guide dosage even after RLAI.