SERUM CONCENTRATIONS AND SIDE-EFFECTS IN PSYCHIATRIC-PATIENTS DURING RISPERIDONE THERAPY

Steady state serum concentrations of risperidone and 9-hydroxy-risperi done (9-OH-risperidone), the active moiety, were measured in 42 patien ts. The concentration-to-dose ratios (C/D) varied by a factor of 20, f rom 1.8 to 36.8 (nmol/l)/(mg/24 hours), and 90% of the active moiety w as constituted of 9-OH-risperidone. No correlation between the serum c oncentration of the active moiety and the side effects evaluated by th e UKU Side Effect Scale was found. The absence of CYP2D6 (poor metabol izers) or the coadministration of drugs other than benzodiazepines inc reased the ratio between parent compound and metabolite but did not si gnificantly influence the C/D of the total active moiety. A therapeuti c range for serum risperidone has not been established, but 6 mg/day i s considered the optimum dose for most patients. The authors found tha t in 90% of 22 patients administered 6 mg/day risperidone, the serum l evels were within 50 to 150 nmol/l.