Chlorproguanil–dapsone (CD) is a fixed-dose anti-folate combination that was developed by a public-private partnership for the treatment of Plasmodium falciparum uncomplicated malaria . CD received approval from the UK Regulatory Agency in July 2003 for the treatment of uncomplicated falciparum malaria in non-pregnant adults. Data from the phase III clinical programme conducted in children in sub-Saharan Africa showed that CD achieved significantly higher cure rates compared to sulphadoxine-pyrimethamine (SP) and was well tolerated . Importantly, CD was active against SP-resistant parasites in Africa [3, 4]. However, and following the significant reduction of haemoglobin (Hb) observed in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency after treatment with CD and artesunate (CDA) in two phase III trials [1, 5], clinical research on this product was stopped and all CD doses already on the market withdrawn .
Dapsone is metabolized in a hydroxylamine metabolite that is susceptible to trigger oxidation damages in red blood cells, leading, if not thwarted by a protection mechanism, to haemolytic anaemia . This is a concern in G6PD-deficient individuals. This genetic polymorphism is particularly prevalent in malaria-endemic areas, and affects about 400 million people worldwide .
G6PD, a cytoplasmic enzyme expressed in all cells, catalyses the first step of the pentose phosphate pathway and plays an essential role in protecting red blood cells from oxidative stress . The G6PD gene is located on the chromosome X, meaning that it mainly affects males. The G6PD gene is highly polymorphic; more than 400 allelic variants have been described, including 34 different mutations with an allelic frequency higher than 1% [10, 11]. According to biochemical characteristics and to genome mutations, G6PD gene is considered as tri-allelic in sub-Saharan Africa: (1) G6PD type B, the most common allelic form, coupled with a normal enzymatic activity, (2) G6PD type A with one point mutation A376G (Asn → Asp) and 85% activity and (3) G6PD type A- with two point mutations A376G and G202A (Val → Met) and 12% activity . In some cases, the second mutation is either G680T or T968G. Other mutations have been occasionally reported, such as A- Betica or A- Sierra Leone . In tropical Africa, G6PD type A- (class III) represents 90% of all G6PD deficiencies.
In a G6PD-deficient individual, oxidative stress can seriously damage red blood cells (reactive oxygen species generation, partial Hb denaturation, Heinz bodies production, membrane function alteration), resulting in acute haemolysis. When acute haemolysis is triggered by a treatment such as CD, Hb drop can be of about 2 g/dl within one or two days after treatment administration . Unlike G6PD Mediterranean, a more severe deficiency in which haemolysis continues until well after the administration of drug is stopped, the haemolytic anaemia caused by G6PD A- is self-limited because only the older red blood cells are destroyed . Epidemiological and in vitro studies suggested that G6PD deficiency could confer a protection against P. falciparum infection by inhibiting erythrocyte invasion or intracellular development of the malaria parasite . Given the current recommendation to use artemisinin-based combination therapy (ACT), in which an artemisinin derivative is combined with another anti-malarial drug, CDA was developed as a low-cost, simple, fixed-dose ACT for use in Africa . However, results of a recent multicentre trial comparing CDA to CD alone showed that, despite its better efficacy, CDA haemolytic risk in G6PD-deficient patients did not allow further use of this treatment . Nevertheless, a multicentre trial including non-co-formulated CDA as a study treatment had already started and a few hundred children had already been included before the decision to stop CDA development was taken. The objective of the study was to assess whether CDA treatment and G6PD deficiency constitute risk factors for a post-treatment Hb drop in African children <5 years of age with uncomplicated malaria.