RESUMEN
Sulphadoxine/pyrimethamine (SP) is often administered with quinine in the treatment of severe falciparum malaria to shorten the course of quinine. The efficacy of SP alone in the treatment of non-severe malaria has been declining rapidly in East Africa, raising concerns of the usefulness of a shortened course of quinine followed SP. We audited the efficacy of quinine/SP in the treatment of severe malaria in Kenyan children. Children with severe falciparum malaria were treated with parenteral quinine followed by a single oral dose of SP. A clinical evaluation was performed 3 weeks later in which a blood sample was obtained for full haemogram, blood slide and analysis of the parasite dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) codons, mutations of which are associated with resistance to SP. A total of 452 children were enrolled, of whom 374 completed the study. Fifty-two (13.9%) children were parasitaemic by 3 weeks of whom 17 (4.5%) had fever as well. The treatment failure group had a significantly higher parasitaemia (129 061 vs. 43 339; P<0.001) and haemoglobin on admission, but only admission parasitaemia independently predicted treatment failure. Those with treatment failure had a significantly lower rise in haemoglobin at 3 weeks compared with treatment successes (9.0 vs. 10.0 g/dl). Of the 76 parasite isolates collected before treatment, 40 (53%) were triple mutant DHFR-double DHPS (Tp-Db), the genotype most associated with SP resistance. Three weeks after SP treatment, the proportion of Tp-Db increased to 72% (31/43). The high treatment failure rate and proportion of parasites with Tp-Db negate the use of SP to shorten the course of quinine treatment in East Africa.
Asunto(s)
Antimaláricos/administración & dosificación , Malaria Falciparum/tratamiento farmacológico , Pirimetamina/administración & dosificación , Quinina/administración & dosificación , Sulfadoxina/administración & dosificación , Administración Oral , Animales , Preescolar , Esquema de Medicación , Combinación de Medicamentos , Femenino , Humanos , Lactante , Infusiones Parenterales , Masculino , Resultado del TratamientoRESUMEN
The genotypes of merozoite surface protein-1, merozoite surface protein-2 and glutamine rich protein are frequently used to distinguish recrudescence from reinfection when parasitaemia reappears after antimalarial drug treatment. However, none of the previous reports has clearly assessed the change of genetic diversity following drug treatment. In the present study, we have assessed the impact of pyrimethamine/sulfadoxine and chlorproguanil/dapsone on the genetic diversity of isolates and the multiplicity of infection in patient isolates from Kilifi, Kenya. We have analysed the length polymorphism of merozoite surface protein-1, merozoite surface protein-2 and glutamine rich protein and the data clearly show that treatment with pyrimethamine/sulfadoxine and chlorproguanil/dapsone did not change the multiplicity of infection found in patients, in contrast to the selection that these drugs exert on the genes encoded by the target enzymes. In addition, we report that children of less than 2 years tend to have fewer numbers of clones per isolate when compared with older children. Overall, this study shows that the selection for genes that confer drug resistance is not a factor in reducing the genetic diversity of parasite clones in a patient.
Asunto(s)
Antimaláricos/farmacología , Resistencia a Medicamentos/genética , Antagonistas del Ácido Fólico/farmacología , Variación Genética/efectos de los fármacos , Malaria/parasitología , Plasmodium falciparum/efectos de los fármacos , Plasmodium falciparum/genética , Distribución por Edad , Alelos , Animales , Antígenos de Protozoos/genética , Antimaláricos/uso terapéutico , Temperatura Corporal , Preescolar , Fiebre/complicaciones , Fiebre/parasitología , Antagonistas del Ácido Fólico/uso terapéutico , Genes Protozoarios/genética , Variación Genética/genética , Humanos , Lactante , Kenia , Malaria/tratamiento farmacológico , Proteína 1 de Superficie de Merozoito/genética , Parasitemia/tratamiento farmacológico , Parasitemia/parasitología , Plasmodium falciparum/crecimiento & desarrollo , Plasmodium falciparum/aislamiento & purificación , Polimorfismo Genético/efectos de los fármacos , Polimorfismo Genético/genética , Proteínas Protozoarias/genéticaRESUMEN
Chemotherapy remains the only practicable tool to control falciparum malaria in sub-Saharan Africa, where >90% of the world's burden of malaria mortality and morbidity occurs. Resistance is rapidly eroding the efficacy of chloroquine, and the combination pyrimethamine-sulfadoxine is the most commonly chosen alternative. Resistant populations of Plasmodium falciparum were selected extremely rapidly in Southeast Asia and South America. If this happens in sub-Saharan Africa, it will be a public health disaster because no inexpensive alternative is currently available. This article reviews the molecular mechanisms of this resistance and discusses how to extend the therapeutic life of antifolate drugs.
Asunto(s)
Antimaláricos/farmacología , Malaria Falciparum/tratamiento farmacológico , Plasmodium falciparum/efectos de los fármacos , Pirimetamina/farmacología , Sulfadoxina/farmacología , África del Sur del Sahara , Animales , Antimaláricos/uso terapéutico , Cloroquina/farmacología , Combinación de Medicamentos , Resistencia a Medicamentos , Humanos , Pruebas de Sensibilidad Microbiana , Mutación , Plasmodium falciparum/genética , Plasmodium falciparum/crecimiento & desarrollo , Pirimetamina/uso terapéutico , Sulfadoxina/uso terapéutico , Tetrahidrofolato Deshidrogenasa/metabolismo , Resultado del TratamientoRESUMEN
Two clinical trials that used Falcidin (Cosmos Ltd., Nairobi, Kenya), the antifolate combination of pyrimethamine/sulfadoxine (PM/SD), as treatment for non-severe falciparum malaria in children at Kilifi, Kenya in 1987-1988 and 1993-1995 have presented an opportunity to assess in vitro the susceptibility trend of Plasmodium falciparum to PM and SD over time on the Kenya coast. The first set of isolates was collected prior to the introduction of PM/SD into the Kenya Medical Research Institute/Wellcome Trust Research unit while the second set was taken soon after PM/SD was introduced in the study area as the first-line treatment drug for uncomplicated falciparum malaria. In the first trial, 69 isolates collected before and after treatment of malaria with PM/SD were tested directly in the field for susceptibility to PM and SD using the standard in vitro micro-test technique, with minimal levels of folate. In the second trial, 97 isolates similarly collected were adapted to culture, and tested as described elsewhere. In both studies, PM and SD susceptibility tests were done separately. There was a highly significant decrease (P < 0.01) in the in vitro sensitivity of P. falciparum isolates to PM and SD between the two trials. In the first trial, the isolates were either sensitive to both PM and SD or resistant to PM and sensitive to SD. During the second trial, isolates were either resistant to PM and sensitive to SD or resistant to both drugs. These results are important in estimating the useful therapeutic life (UTL) of PM/SD in this area and in identifying alternative antifolate drugs.
Asunto(s)
Antimaláricos/farmacología , Plasmodium falciparum/efectos de los fármacos , Pirimetamina/farmacología , Sulfadoxina/farmacología , Animales , Niño , Preescolar , Dihidropteroato Sintasa/genética , Resistencia a Medicamentos , Humanos , Lactante , Mutación , Pruebas de Sensibilidad Parasitaria , Tetrahidrofolato Deshidrogenasa/genética , Factores de TiempoRESUMEN
Pyrimethamine (PM) plus sulfadoxine (SD) is the last remaining affordable drug for treating uncomplicated malaria in Africa. The selective pressure exerted by the slowly eliminated combination PM/SD was compared with that exerted by the more rapidly eliminated combination chlorproguanil/dapsone (CPG/Dap) on Kenyan Plasmodium falciparum. Point mutations were analyzed in dihydrofolate reductase and dihydropteroate synthase and in the genetic diversity of 3 genes in isolates collected before and after CPG/Dap and PM/SD treatments. PM/SD was associated strongly with the disappearance of fully drug-sensitive parasites and with a significant increase in the prevalence of resistant parasites in subsequent parasitemias. However, this was not a characteristic of treatment with CPG/Dap. Moreover, most of the patients who returned with recrudescent infections were in the PM/SD-treated group. The data predict a longer useful therapeutic life for CPG/Dap than for PM/SD, and, thus, CPG/Dap is a preferable alternative for treatment of chloroquine-resistant falciparum malaria in sub-Saharan Africa.
Asunto(s)
Antimaláricos/administración & dosificación , Dapsona/administración & dosificación , Antagonistas del Ácido Fólico/administración & dosificación , Plasmodium falciparum/efectos de los fármacos , Proguanil/análogos & derivados , Pirimetamina/administración & dosificación , Sulfadoxina/administración & dosificación , Animales , Combinación de Medicamentos , Resistencia a Medicamentos , Péptido Sintasas/genética , Proguanil/administración & dosificación , Tetrahidrofolato Deshidrogenasa/genéticaRESUMEN
The antifolate combination of pyrimethamine (PM) and sulfadoxine (SD) is the last affordable drug combination available for wide-scale treatment of falciparum malaria in Africa. Wherever this combination has been used, drug-resistant parasites have been selected rapidly. A study of PM-SD effectiveness carried out between 1997 and 1999 at Kilifi on the Kenyan coast has shown the emergence of RI and RII resistance to PM-SD (residual parasitemia 7 days after treatment) in 39 out of 240 (16.25%) patients. To understand the mechanism that underlies resistance to PM-SD, we have analyzed the dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) genotypes of 81 patients. Fifty-one samples were obtained, before treatment, from patients who remained parasite free for at least 7 days after treatment. For a further 20 patients, samples were obtained before treatment and again when they returned to the clinic with parasites 7 days after PM-SD treatment. Ten additional isolates were obtained from patients who were parasitemic 7 days after treatment but who were not sampled before treatment. More than 65% of the isolates (30 of 46) in the initial group had wild-type or double mutant DHFR alleles, and all but 7 of the 47 (85%) had wild-type DHPS alleles. In the paired (before and after treatment) samples, the predominant combinations of DHFR and DHPS alleles before treatment were of triple mutant DHFR and double mutant DHPS (41% [7 of 17]) and of double mutant DHFR and double mutant DHPS (29% [5 of 17]). All except one of the posttreatment isolates had triple mutations in DHFR, and most of these were "pure" triple mutants. In these isolates, the combination of a triple mutant DHFR and wild-type DHPS was detected in 6 of 29 cases (20.7%), the combination of a triple mutant DHFR and a single mutant (A437G) DHPS was detected in 4 of 29 cases (13.8%), and the combination of a triple mutant DHFR and a double mutant (A437G, L540E) DHPS was detected in 16 of 29 cases (55.2%). These results demonstrate that the triply mutated allele of DHFR with or without mutant DHPS alleles is associated with RI and RII resistance to PM-SD. The prevalence of the triple mutant DHFR-double mutant DHPS combination may be an operationally useful marker for predicting the effectiveness of PM-SD as a new malaria treatment.