Interactions among primaquine, malaria infection and other antimalarials in Thai subjects.

1. The pharmacokinetics of rac-primaquine (45 mg base) and its principal plasma metabolite, carboxyprimaquine have been investigated in healthy Thai adults prior to and following a single oral dose of mefloquine (10 mg kg-1). 2. Primaquine was rapidly absorbed, attaining peak plasma concentrations (median and range) of 167 (113-532) micrograms l-1 in 2 (1-4) h. Thereafter, concentrations declined rapidly with an apparent terminal half-life of 6.1 (1.7-16.1) h and an oral clearance (CLpo) of 33.1 (17.6-49.3) l h-1. Administration of mefloquine had no effect on the values of any of these parameters at the 5% level of significance [Cmax 229 (114-503) micrograms l-1; tmax 3 (2-4) h; t1/2,z 3.9 (1.7-13.5) h; CLpo 34.0 (21.7-49.0) l h-1]. 3. The carboxylic acid metabolite of primaquine achieved maximum concentrations (median and range) of 890 (553-3634) micrograms l-1 at 6 (3-16) h. Thereafter, plasma concentrations of carboxyprimaquine declined to 346 (99-918) micrograms l-1 at 24 h. AUC (0,24 h) was 12737 (6837-27388) micrograms l-1 h. Administration of mefloquine had no effect on the plasma concentrations of this metabolite [Cmax 1035 (174-3015) micrograms l-1; tmax 8 (2-24) h; AUC(0,24) 13471 (2132-17863) micrograms l-1 h]. 4. The effect of falciparum malaria and treatment with quinine (10 mg salt kg-1 p.o.) on the pharmacokinetics of primaquine (45 mg base p.o.) has been investigated in adult Thai patients during and after infection with falciparum malaria.(ABSTRACT TRUNCATED AT 250 WORDS)