On the question of interindividual variations in chloroquine concentrations.

In a review of studies using appropriate methods for drug determinations and controlled intake, an interindividual variation in chloroquine concentrations of 2.3 to 5.6-fold was found. In our department, steady-state concentrations were evaluated in 40 patients with rheumatic diseases. The variation in whole blood concentrations was 11-fold for chloroquine and 10-fold for the desethylchloroquine metabolite. The mean ratio between desethylchloroquine and chloroquine concentrations was 0.53 and the Spearman-Rank correlation 0.92. The correlation between age and the ratio of chloroquine concentration/dose was 0.36 (P < 0.05) and the corresponding correlation for body weight was -0.43 (P < 0.05). Our data indicate that body weight and age are important independent factors for the disposition of chloroquine. However, when extensive 100-fold variations in concentrations are found between individuals we suggest that the reliability of the dose intake should be questioned.