Studies of mefloquine bioavailability and kinetics using a stable isotope technique: a comparison of Thai patients with falciparum malaria and healthy Caucasian volunteers.

1 A mefloquine hydrochloride tablet (250 mg base equivalent to 4.8 +/- 0.6 mg kg-1; mean +/- s.d.) and deuterium labelled mefloquine hydrochloride solution (250 mg base) were given to six adult male Thai patients with acute falciparum malaria and six healthy Swiss adult male volunteers (equivalent to 3.5 +/- 0.1 mg kg-1). 2 The relative bioavailability of the tablet formulation derived from comparison of the areas under the plasma concentration-time curves was similar in both groups; 87 +/- 11% and 89 +/- 10% (mean +/- s.d.). 3 The rate of drug absorption appeared to be similar in the two groups but peak plasma mefloquine concentrations were approximately three times higher in the Thai patients (1004 +/- 276 ng ml-1 for the tablet and 1085 +/- 280 ng ml-1 for the suspension) compared with the Swiss volunteers (319 +/- 73 ng ml-1 for the tablet, and 369 +/- 121 ng ml-1 for the suspension). 4 Estimates of the oral clearance CLpo of unlabelled mefloquine were significantly lower (17.5 +/- 4.4 ml h-1 kg-1) in the Thai patients compared with 28.8 +/- 3.5 ml h-1 kg-1 in the Swiss volunteers; P less than 0.05). Terminal elimination half-lives were significantly shorter in the patients (10.3 +/- 2.5 days) than in the volunteers (16.7 +/- 1.9 days; P less than 0.005). Differences of a similar magnitude were observed when comparing the pharmacokinetic parameters derived from the deuteromefloquine plasma concentrations. 5 Both genetic and disease related factors are likely to account for the large pharmacokinetic differences between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)