In vivo and in vitro sensitivity of Falciparum malaria to quinine in Thai children.

The study was carried out to assess the efficacy of quinine in children with Falciparum malaria in relation to in vitro sensitivity (measured in terms of minimum inhibitory concentration: MIC) and to trough serum levels of quinine during the course of treatment. Fifty children aged ten months to 12 years with Falciparum malaria were randomly divided into two groups. Group I: 24 children were treated with quinine 10 mg base per body weight every eight hours for 14 days. Group II: 26 children were treated with quinine at the dosage adjusted to the body surface area based on an adult dose of 500 mg base eight hourly for 14 days. There were three treatment failures, one RI and one RII in group I, and one RI in group II. The serum concentrations of quinine reached a peak level on day two and levelled off by the end of the first week. Concentrations in group II were higher than in group I. The mean minimal inhibitory concentration (MIC) of quinine in the two groups was 14.89 nmol per ml ranging from 8-26 nmol per ml. In cases with treatment failure, the trough serum quinine levels became lower than the corresponding MIC after day six (RI) and after day two (RII). The rise of MIC suggests that sensitivity of Falciparum malaria parasites to quinine may be decreasing in Thailand. Failures of treatment in standard dosage may occur in cases infected by parasites with high MIC, in which trough serum quinine levels cannot be maintained above the MIC longer than six days during the course of treatment. However in one cured case, the trough serum quinine levels were below the MIC throughout treatment. More research is needed on the real relationship between serum quinine concentrations, the MIC, and clinical and parasitological response to quinine.