The therapeutic efficacy of sulfadoxine/pyrimethamine against Plasmodium falciparum in Yemen.

OBJECTIVE: The aim of this study was to determine the sensitivities of Plasmodium falciparum clinical isolates to sulfadoxine/pyrimethamine (SP) using in vivo and in vitro methods. SUBJECTS AND METHODS: In vivo and Mark III in-vitro test techniques according to World Health Organization protocols of antimalarial drug tests were used to determine the SP susceptibility of the P. falciparum isolates from 100 malaria patients of both sexes between the ages of 3.5 and 45 years and living in Tihamah, Yemen. The study was conducted between 19 March and 12 May 2005. RESULTS: In vivo: no therapeutic failure occurred; the clinical outcome matched the parasitological response and all patients were parasite free by day 3 and remained so on days 7, 14 and 28. In vitro: all the P. falciparum isolates developed to schizonts in zero-drug-concentration wells, but were inhibited in 40 nmol/l of SP; the mean effective concentration (EC(99)) was 67.17 nmol/l. CONCLUSION: Our findings showed that the SP combination is still effective for the treatment of uncomplicated P. falciparum malaria in Yemen. It is recommended that further studies be carried out to address the importance of dihydropteroate synthetase/dihydrofolate reductase mutations as predictive markers of sulfadoxine/pyrimethamine resistance in Yemen.

The prevalence and degree of resistance of Plasmodium falciparum to first-line antimalarial drugs: an in vitro study from a malaria endemic region in Yemen.

BACKGROUND: Unpublished studies on antimalarial drug efficacy have found low levels of chloroquine resistance in Yemen. This study was carried out to determine the current prevalence of drug resistance in Plasmodium falciparum in Yemen to the main anti-malarial drugs and to determine the effective concentration(EC) values. METHODS: The WHO standard protocol was used for the selection of subjects, collection of blood samples, culture techniques, examination of post-culture blood slides and interpretation of results. The in vitro micro-test Mark III was used for assessing susceptibility of P. falciparum isolates. RESULTS: The criteria for blood parasite density was met by 219 P. falciparum malaria patients. Chloroquine resistance was found in 47% of isolated P. falciparum schizonts. Mefloquine resistanfce was found in 5.2%. In addition, the EC50 and EC95 values in blood that inhibited schizont maturation in resistant isolates were higher than the normal therapeutic level of mefloquine. No resistance occurred against quinine or artemisinin, with no growth at hte cut-off level of quinine and inhibition of low concentrations of artemisinin. CONCLUSION: Our study confirmed the occurrence of chloroquine-resistant P. falciparum and a slow increase in the rate of this resistance; it is likely that resistance will increase further and spread over all the foci of malaria in Yemen. The low rate of mefloquine-resistant P. falciparum, was lower than that reported in Africa or Southeast Asia, but it is the first report of mefloquine resistance in Yemen. Finally, the isolates were sensitive to low-concentrations of quinine and artemisinin.