In vitro blood schizonticidal activity of sera containing mefloquine‐quinine against Plasmodium falciparum

Serum samples collected at intervals from healthy volunteers, after the administration of 3 drug regimens (quinine (QN) 600 mg, mefloquine (MQ) 750 mg, and MQ 750 mg plus QN 600 mg) were investigated for their blood schizonticidal activities against K₁ strain Plasmodium falciparum in vitro . Superiority of activity was shown in the sera collected after the combination regimen. In the diluted sera of the QN regimen, a complete inhibitory effect was observed for only 24 hours, whereas the effect was sustained for 72 hours in the sera collected after MQ in either regimen (MQ alone or MQ/QN). The pattern of minimum inhibitory concentrations (MICs) of QNEq of the sera from QN alone was constant throughout a 24‐hour period, with significantly higher concentrations than that from the combination regimen (118–150 vs 21.25–73.5 μg/l). In sera collected after the combination regimen, however, the MIC gradually decreased from 0.5 until 2.5 and 4 h, and thereafter gradually returned to the same levels again during a period of 6–24 hours. The MICs of MQEq when given as MQ alone or in combination appeared constant, with a significantly higher value in the former regimen (24.4–26.8 vs 17–19.2 μg/l).