In vitro sensitivity of Plasmodium falciparum isolates in Thailand to quinine and chloroquine, 1984-1990.

Until now, quinine has been used worldwide as the drug of choice for the emergency treatment of severe and complicated malaria. In fact, the long­ standing dependability of quinine has created a context of clinical confidence and reduced the per­ ceived threat of P. Jalciparum recrudescence where quinine and quinidine are available. However, in a situation of substantial loss of efficacy, it is conceivable that the life-saving properties of quinine may be challenged. We have therefore analysed data on the in vitro sensitivity to quinine of Plas­ modium Jalciparum (pf) isolates collected from various parts of Thailand from 1984 to 1990. The investigation included also the in vitro response to chloroquine. Details of materials and methods of the study can be found in an earlier report on the in vitro sensitivity of pf to mefloquine and halofan­ trine (Wongsrichanalai et ai, 1992). Basically, we used two in vitro methods to determine the sus­ ceptibility of pf isolates, one using morphological reading (Rieckmann et ai, 1978; Childs and Pang, 1988) and the other measuring radioisotope incor­ poration (Desjardins et ai, 1979; Webster et ai, 1985). For both methods, inhibition of growth or schizont maturation is expressed as the SO-percent inhibitory concentration (lCSO). The diphosphate salts of quinine and chloroquine were used in all tests.