Effect of Co-administration of Promethazine on the U.V. Analysis of Chloroquine in Man.
Promethazine hydrochloride is commonly co-administered with chloroquine phosphate to treat chloroquine-induced pruritus. In monitoring drug levels of one drug on co-administration with another, separation of both drugs is often carried out in the biological fluid before the final analysis to eliminate interference. The pharmacokinetics of a drug may be markedly affected by a concomitant administration of a second drug, leading to differences in the plasma drug concentrations. The extent, if any, that, the co-administration of promethazine hydrochloride and chloroquine phosphate affects the U.V-analysis of chloroquine and some aspects of the absorption/excretion pattern of chloroquine, is the basic question for which this research seeks to provide answers. Blood and urine samples were monitored by the U.V. method, at various intervals, from subjects to whom were intramuscularly administered chloroquine phosphate alone, in conjunction with promethazine hydrochloride and promethazine hydrochloride (control). The total drug concentration of chloroquine was monitored. In this study, the area under the concentration-time curve, the cumulative excretions of the total drug were compared when chloroquine phosphate was administered alone and in conjunction with promethazine hydrochloride. Results showed that promethazine hydrochloride affects the absorption profile of chloroquine (as indicated by AUC measurements) and its excretion profile (as indicated by measurement of the cumulative excretion). In conclusion, operating within the recommended therapeutic range, promethazine hydrochloride does not affect the U.V. absorbance of chloroquine in biological media.