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)