BIOAVAILABILITY OF HYDROXYCHLOROQUINE TABLETS IN PATIENTS WITH RHEUMATOID ARTHRITIS

Nine patients with RA received two doses of 155 mg racemic hydroxychloroquineeach, as a tablet and by i.v. infusion, in a randomized cross-overdesign study. Blood concentrations over the first 32 h followingeach dose were determined. Bioavailability was estimated usinga sequential exponential least squares deconvolution method. The mean fraction absorbed from the tablet was 0.79 (range 0.39to 1.27). The mean absorption lag-time was 1.3 h (range 0.5to 3.7 h) and the mean time for 50% absorption was 4.3 h (range1.9 to 10.3 h). Mean rate and extent of hydroxychloroquine absorptionwere not significantly different from that previously reportedfor healthy volunteers, although the interindividual variabilityin absorption parameters was greater in the patient group. Variabilityin the extent of absorption would lead to differences in steady-statehydroxychloroquine concentrations between patients, potentiallycontributing to the variability in response observed in clinicalpractice. KEY WORDS: Pharmacokinetics, Hydroxychloroquine, Bioavailability Present address: Department of Pharmacy, University of Manchester,Manchester M13 9L