Single-dose investigation of possible interactions between the components of the antimalarial combination Fansimef

Fansimef is a new oral schizonticide which contains pyrimethamine (P), sulfadoxine (S) and mefloquine (M) in a weight ratio of 1:20:10. This antimalarial combination is highly active against multi-resistant Plasmodium falciparum and in vitro studies showed that the resistance development by plasmodia against this combination is considerably delayed. The single-dose pharmacokinetics of the three Fansimef components were investigated in 10 Caucasian volunteers with special emphasis on possible mutual kinetic interactions. For this reason the same subjects received successively tablets of Fansimef (P + S + M), Fansidar (P + S) and mefloquine alone. Following administration of Fansimef all three components revealed long elimination half-lives (P = 88 h, S = 183 h, M = 437 h) and high binding to plasma proteins (P = 92.5%, S = 87.6%, M = 97.6%). The apparent volume of distribution in the postdistributive phase (VD beta/F) was small for S (0.13 l/kg) but amounted to 2.1 l/kg for P and reached even 11.8 l/kg in the case of M. The systemic clearance (ClTS/F) showed almost identical values for P and M, namely approximately equal to 19 ml/h/kg, while sulfadoxine reached only a value of 0.5 ml/h/kg. Almost identical pharmacokinetic parameters (p greater than 0.05) were found after administration of Fansidar or M alone. Therefore one can exclude any significant interaction between the single components of the Fansimef combination. In addition, animal studies showed that synergism of the toxicity of the three combination partners can be excluded.