The use of a side effect as a qualitative indicator of plasma chlorpromazine levels

Chlorpromazine (CPZ) is widely used in South African hospitals. The purpose of this study was to determine whether any physiological parameter (side-e ffect) could be correlated with plasma concentrations of CPZ or its metabol ites. In the absence of a blood level, such a correlation could serve as a qualitative indicator of the amount of chlorpromazine in the body. Such a m arker can assist the psychiatrist with therapeutic decisions regarding poor compliance and the lack of response with the drug. Fifteen schizophrenic p atients were included in this study and regression analysis was used to det ermine any correlation between CPZ, 7-hydroxychlorpromazine, Chlorpromazine -N-oxide, Nor(1) chlorpromazine, Nor(2)chlorpromazine, chlorpromazine sulfo xide, Nor(2) chlorpromazine sulfoxide and blood pressure, pulse rate, sedat ion and finger tremor. No correlation was seen between blood pressure or pu lse rate and plasma concentrations of CPZ or the metabolites. A good correl ation was seen between sedation, 7-hydroxychlorpromazine (P=0.035) and chlo rpromazine sulfoxide (P=0.016). The results suggest that as the levels of c hlorpromazine sulfoxide increase, the probability of sedation increases, wh ile increasing levels of 7-hydroxychlorpromazine have the opposite effect. A good correlation was also seen between finger tremor and chlorpromazine l evels (P=0.035). These results suggest that there is a 50% probability that the patient would experience finger tremor when the plasma concentration o f chlorpromazine is 46 ng/ml. This study demonstrated the potential for the use of sedation and finger tremor as qualitative indicators of the plasma concentration of CPZ and two metabolites. Further studies with larger patie nt numbers are warranted. (C) 1999 Elsevier Science B.V./ECNP. All rights r eserved.