Chloroquine and desethylchloroquine in plasma, serum, and whole blood: problems in assay and handling of samples.

A spectrophotofluorometric method for determination of chloroquine in body fluids was compared with a recently developed high performance liquid chromatographic (HPLC) method. The spectrophotofluorometric method was found to codetermine the main metabolite desethylchloroquine and thus to give higher "chloroquine" concentrations than the HPLC method. The concentrations determined with spectrophotofluorometry roughly corresponded to the calculated sum of chloroquine and desethylchloroquine as determined with the HPLC method. The concentrations of chloroquine and desethylchloroquine were higher in serum, and considerably higher in whole blood, than in plasma. The duration and force of centrifugation greatly influenced the concentrations of chloroquine and desethylchloroquine found in plasma. The concentrations decreased as centrifugal force increased reaching relatively stable levels at 500 g. Increasing the centrifugation time partly compensated for lower g forces. These methodological problems can be avoided by using whole blood for determinations of chloroquine. Since the biological activities of desethylchloroquine and chloroquine are not the same, drug monitoring should be performed with a method distinguishing between the parent drug and the metabolite.