EFFECT OF PREVIOUS CHLOROQUINE INTAKE ON IN-VIVO PLASMODIUM-FALCIPARUM DRUG-SENSITIVITY

Investigation of the in vivo response of P. falciparum malaria parasit es to chloroquine was conducted during 1993/94 in Al-Ain District of A bu Dhabi Emirate, UAE, Sixty seven expatriates who developed falciparu m malaria on their return from Pakistan, Oman and Sudan were recruited for the WHO in vivo tests, Of the 67 patients, eight were classified as having RII and RIII responses, while 59 remained aparasitaemic at t he end of the seven-day WHO standard test, On continuation into the 28 -day WHO extended test, a further 34 patients exhibited RI resistance, Resistance of parasites to chloroquine was confirmed by measurement o f plasma chloroquine using High-Performance Liquid Chromatography, In all 67 patients, the level of chloroquine was wen above the minimum th erapeutic level, The outcome of the in vivo test in patients treated f or the first time was significantly different from that in patients wh o were previously on chloroquine, Among patients treated for the first time, 36 out of 41 (88%) had a resistant response, whereas, among tho se previously on chloroquine only six out of 26 (23%) had a resistant response, The difference is probably due to the higher initial plasma level of chloroquine among patients who were previously on the drug. C uring more patients with higher plasma chloroquine implies that chloro quine shall continue to-be useful, particularly if resistance is at th e RI level, Appropriate higher therapeutic levels of chloroquine shoul d be defined for such patients.