Resistance of Plasmodium falciparum to sulfadoxine-pyrimethamine combination in semi-immune children in Zaria, northern Nigeria

Effects of pyrimethamine versus proguanil in malarial chemoprophylaxis in children with sickle cell disease: a randomized, placebo-controlled, open-label study

BACKGROUND

Malarial chemoprophylaxis is essential for patients with homozygous sickle cell disease (SCD) who live in areas where malaria is endemic. Endemic regions include most sub-Saharan African countries and Southeast Asia.

OBJECTIVE

This study compared the efficacy and tolerability of pyrimethamine with that of proguanil and placebo in the prevention of malaria and the complications of Plasmodium falciparum infection (hepatomegaly, splenomegaly, bone pain crisis, hemolytic crisis) in children with SCD.

METHODS

In this single-center, open-label study conducted in Nigeria, children aged 1 to 16 years with SCD were randomly assigned to receive tablets of pyrimethamine (0.5 mg/kg·wk), proguanil (1.5 mg/kg·d), or placebo (vitamin C, 7 mg/kg·d) for 9 months as prophylaxis from February to December (which includes the rainy season), the period of greatest malarial transmission. The clinical and laboratory features of malaria (presence of parasitemia, parasite count and density, hepatomegaly and/or splenomegaly, symptomatic malarial infection [fever, rigors], bone pain crises, and hemolytic crises) were assessed.

RESULTS

A total of 97 patients completed the study (49 boys, 48 girls; mean [SD] age, 7.8 [4.3] years). The pyrimethamine group comprised 36 patients (mean [SD] age, 8.1 [4.3] years; range, 2-16 years); the proguanil group, 32 patients (mean [SD] age, 9.5 [3.7] years; range, 3-16 years); and the placebo group, 29 patients (mean age, 5.9 years; range, 1-14 years). The male:female ratio was 1.1:1 in the pyrimethamine group, 1:1.7 in the proguanil group, and 1.6:1 in the placebo group. Parasitemia was noted in 7 patients (19.4%) in the pyrimethamine group, 6 (18.8%) in the proguanil group, and 7 (24.1%) in the placebo group at the start of the study. P falciparum was the only isolate. The mean parasite density over the 9-month period was significantly lower with proguanil compared with pyrimethamine (P = 0.045) and placebo (P<0.05). The incidence of splenomegaly was least with pyrimethamine, but this group had the most patients clinically diagnosed with malaria. Hospitalizations and episodes of bone pain and hemolytic crisis occurred most frequently with placebo. One patient in the placebo group died of septicemia.

CONCLUSIONS

Proguanil and pyrimethamine both reduced parasitemia; however, proguanil significantly decreased mean parasite density more effectively than pyrimethamine. Pyrimethamine and proguanil may protect children with SCD from the complications of P falciparum infection despite persistent parasitemia. Proguanil may be more useful than pyrimethamine in the prevention of bone pain crises among patients with SCD.

Strategies for the prevention of antimalarial drug resistance: rationale for combination chemotherapy for malaria

Among the several 'tropical' diseases that affect humans, malarin poses special control problems due to the increasing population at risk from the disease, the difficulties in eradicating the mosquito vector in the tropics and the emergence and spread of parasite resistance to commonly used antimalarial drugs. There is both clinical experience and experimental evidence that, however effective when first introduced, the lifespan of drugs is inevitably curtailed by the emergence of resistant parasites. Resistance is the most important factor in determining the useful lifespan of antimalarial drugs. In this review, Nick White and Piero Olliaro discuss the rationale for combination chemotherapy.

Mefloquine chemoprophylaxis in Chinese railway workers on contract in Nigeria

BACKGROUND

Nonimmune Chinese nationals on a 2-year railway contract job were commenced on mefloquine (MQ) chemoprophylaxis 20 weeks after arrival in Nigeria. The objective of the study was to determine the usefulness of mefloquine (MQ) (despite the delay in starting) and its tolerability in this group.

METHODS

Ninety-one workers (89 males, 2 females) were commenced on weekly MQ 250 mg doses for 17 weeks. Most of the subjects were followed up to 16 weeks after cessation of chemoprophylaxis. The morbidity pattern before, during, and after cessation of chemoprophylaxis was compared.

RESULTS

Of the 91 workers included in the study, 89 were evaluable. Three (3.37%) of these developed clinical illness during the 17-week period of chemoprophylaxis. This protection was highly significant when compared to 23 of 91 people (25.27%) who developed clinical illness before chemoprophylaxis was commenced (RR 0.13, 95% CI 0.04-0.43, p <.001). The risk of developing acute malaria increased more than three times, among 84 members of the group who were followed up to 16 weeks after MQ was discontinued (RR 3.18, 95% CI 0.89-11.34). Two subjects withdrew after the second dose due to adverse reactions, however the remaining 89 subjects tolerated the drug for the 16-week period.

CONCLUSIONS

Mefloquine significantly reduced malaria morbidity in the study group. Pretravel counseling and advice is important in preventing unnecessary deaths and morbidity in nonimmune travelers to malarious areas.

Responses of multidrug-resistant Plasmodium falciparum parasites to mefloquine in Nigerian children

Thirty-three children aged 6 months to 7 years from an area with multidrug-resistant Plasmodium falciparum strains were treated with 25 mg/kg body weight of mefloquine base as a single oral dose. They were followed-up using the modified 28-day WHO extended field test. The parasite isolates from these patients were cultured in vitro with different concentrations of mefloquine. All children were parasite-negative by day 4, and 31 remained so throughout the period of observation. Two patients who were parasitaemic on days 16 and 28 were successfully treated with a sulphadoxine/pyrimethamine combination. Parasitological and clinical responses were well correlated. The mean parasite clearance time was 65 +/- 10.2 hours. A mefloquine concentration of 64 pmol/well inhibited schizont growth and the EC50 and EC99 were 5.5 and 5.4 pmol/well (1.1 and 10.8 mumol/l blood) respectively. This indicates reduced parasite susceptibility to the drug in vitro.

Sensitivity of Plasmodium falciparum to reduced dose of mefloquine in pregnant women in Nigeria

Mefloquine base, (12.5 mg/kg body weight), was administered as a single oral dose to 34 pregnant women with Plasmodium falciparum parasitaemia. They were followed up in vivo using the modified 28-day WHO extended field test. The sensitivity of P. falciparum isolates obtained from these women to mefloquine (MQ) was evaluated in vitro. All women were parasite negative by day 4 and remained aparasitaemic throughout the 28-day period of observation. Parasitological and clinical responses were well correlated in all the patients. Minimal side effects, after drug intake, were reported by these women, but they all resolved spontaneously. The determined Mean Parasite Clearance Time (MPCT) was 57.7 +/- 14 hours. Seventeen parasite isolates were cultured in vitro; 9 (53%) grew satisfactorily. Schizont growth inhibitions was obtained at mefloquine concentration of 32 pmol/well (6.4 pmol/mu L). The effective drug concentration that gave 99% parasite growth inhibition (EC99) was 25.6 pmol/well (5.1 pmol/mu L); which indicates high parasite susceptibility to the drug in vitro. However, low dose of MQ may be ineffective in clearing parasitaemia in areas with mefloquine resistant parasite strains.

Antimalarial drug response of Plasmodium falciparum from Zaria, Nigeria

The sensitivity of Zaria strains of Plasmodium falciparum to chloroquine, mefloquine, quinine and sulphadoxine/pyrimethamine was investigated 5 years after the appearance of in vivo/in vitro chloroquine resistance in urban Zaria. Infections in 36/43 children (83.7%) treated with chloroquine were sensitive while those in 7 (16.3%) were resistant. 8/13 isolates cultured (61.5%) were sensitive in vitro to chloroquine and 5 (38.5%) were resistant. Of the cultured isolates, 13/13 (100%), 12/13 (92.3%) and 5/7 (71.4%) showed mefloquine, quinine and sulphadoxine/pyrimethamine sensitivity, respectively. The results confirmed chloroquine and sulphadoxine/pyrimethamine resistance in urban Zaria and revealed emerging quinine resistance. Resistance to chloroquine and sulphadoxine/pyrimethamine is at RI level and chloroquine should continue to be the first-line drug for the treatment and prevention of P. falciparum infection in the Zaria area of northern Nigeria. We suggest that, while quinine serves as second-line drug, mefloquine should be reserved for infections resistant to chloroquine, quinine and sulphadoxine/pyrimethamine.

In vitro activities of novel antifolate drug combinations against Plasmodium falciparum and human granulocyte CFUs

The potency of antimalarial dihydrofolate reductase inhibitors, alone and in synergistic combination with dihydropteroate synthetase inhibitors, against the Kenyan K39 strain of Plasmodium falciparum (pyrimethamine resistant) and against normal replicating human bone marrow cells in in vitro culture has been studied. Therapeutic indices and rank order of synergistic potency were derived. Trimethoprim, pyrimethamine, and the quinazolines WR159412 and WR158122 had the smallest therapeutic indices (1.39, 4.38, 2.56, and 90.0, respectively), while the three triazines clociguanil, WR99210, and chlorcycloguanil had the largest (3,562, 3,000, and 2,000, respectively). In rank order of decreasing activity against P. falciparum, the six most potent drug combinations were WR99210-dapsone, chlorcycloguanil-dapsone, WR158122-dapsone, WR159412-dapsone, WR159412-sulfamethoxazole, and chlorcycloguanil-sulfamethoxazole; pyrimethamine-sulfadoxine was the least potent combination. These experiments form a basis for the selection of rapidly eliminated antifolate combinations for further clinical testing.

A mutation-specific PCR system to detect sequence variation in the dihydropteroate synthetase gene of Plasmodium falciparum

Sulphur-based antimalarial drugs targeted at dihydropteroate synthetase (DHPS) are frequently used in synergistic combination with inhibitors of dihydrofolate reductase (DHFR) to combat chloroquine-resistant malaria. We have previously shown that lines of Plasmodium falciparum resistant to the most commonly used sulpha drug, sulphadoxine, carry point mutations in the DHPS coding region, relative to the sequence of sensitive strains (Brooks et al., Eur. J. Biochem. 224 (1994) 397-405). We have now developed PCR diagnostic assays based on allele-specific amplification that are able to detect such mutations. The four tests described can reliably discriminate all of the mutations observed to alter codons 436, 581 and 613, yielding allele-specific amplification products of different sizes in each case. Moreover, by careful adjustment of primer length and the degree of mismatch to target and non-target alleles, we were able to standardise all four tests to a single set of PCR conditions, allowing all possible mutations to be monitored simultaneously on one thermocycler. These assays should prove invaluable in further assessing the contribution of specific base changes in the DHPS gene of the parasite to the sulphadoxine resistance phenotype and to the clinical failure of the sulphadoxine/pyrimethamine combination Fansidar.

Sequence variation of the hydroxymethyldihydropterin pyrophosphokinase: dihydropteroate synthase gene in lines of the human malaria parasite, Plasmodium falciparum, with differing resistance to sulfadoxine

Dihydropteroate synthase (H2Pte synthase) is the target of the sulfur-based antimalarial drugs, which are frequently used in synergistic combination with inhibitors of dihydrofolate reductase (H2folate reductase) to combat chloroquine-resistant malaria. We have isolated the H2Pte synthase coding sequence of the most pathogenic human parasite Plasmodium falciparum. It forms part of a longer coding sequence, located on chromosome 8, that also specifies 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (CH2OH-H2pterinPP kinase) at its 5' proximal end. This domain is unusually large, with two long insertions relative to other CH2OH-H2pterinPP kinase molecules. To investigate a possible genetic basis for clinical resistance to sulfa drugs, we sequenced the complete H2Pte synthase domains from eleven isolates of P. falciparum with diverse geographical origins and levels of sulfadoxine resistance. Overall, point mutations in five positions were observed, affecting four codons. Parasite lines exhibiting high-level resistance were found to carry either a double mutation, altering both Ser436 and Ala613, or a single mutation affecting Ala581. The mutations at positions 436 and 581 have the same location relative to each of two degenerate repeated amino acid motifs that are conserved across all other known H2Pte synthase molecules. The amino acid alteration at residue 613 is identically positioned relative to a different conserved motif. The fourth amino acid residue (437) affected by mutation, though adjacent to the apparently crucial residue 436, shows no obvious correlation with resistance. Although these mutations have no exact counterparts in any other organism, that at position 581 falls within a region of three amino acids where H2Pte synthase is modified in various ways in a number of sulfonamide-resistant pathogenic bacteria. Copy-number analysis indicated that there was no amplification of the H2Pte synthase domain in resistant parasite lines of P. falciparum, compared to sensitive lines.

A single dose of intramuscular sulfadoxine-pyrimethamine as an adjunct to quinine in the treatment of severe malaria: pharmacokinetics and efficacy

It has been suggested that sulfadoxine-pyrimethamine (SD/PM) may be useful in the treatment of severe malaria since it could enhance the killing of parasites by quinine (QN) and it can be given as a single intramuscular injection. Eighty Kenyan children with severe malaria were allocated at random to receive either intramuscular QN alone (quinine dihydrochloride 20 mg salt/kg as a loading dose, followed by 10 mg salt/kg 12 hourly for a total of 6 doses) or the same QN regimen plus one intramuscular injection of SD/PM (sulfadoxine 25 mg/kg, pyrimethamine 1.25 mg/kg). There was no difference in time to defervescence, aparasitaemia, or 50% reduction in parasitaemia, parasite elimination half-life, or mortality between the 2 groups. In addition, the concentrations of SD and PM were measured in 14 children and of QN in 8 of these children. Concentrations needed to achieve synergy against PM-resistant strains of Plasmodium falciparum were achieved in all of the children with severe malaria within the first hour and maintained for more than 72 h. SD/PM did not perturb the pharmacokinetics of QN.

The disposition of oral and intramuscular pyrimethamine/sulphadoxine in Kenyan children with high parasitaemia but clinically non-severe falciparum malaria

1. H.p.l.c. methods are described for the measurement of pyrimethamine and sulphadoxine in small volumes of plasma dried on filter paper strips. 2. Pyrimethamine/sulphadoxine (Fansidar, Hoffman LaRoche) was given by mouth and by intramuscular injection to children with uncomplicated falciparum malaria but with high parasitaemia (n = 8 for both routes; pyrimethamine 1.25 mg kg-1, sulphadoxine 25 mg kg-1). 3. Plasma concentrations of pyrimethamine and sulphadoxine associated with synergistic effects against pyrimethamine-resistant strains of Plasmodium falciparum in vitro were achieved within 1 h of administration and were maintained beyond the end of sampling. 4. After both oral and parenteral administration the plasma concentrations of both compounds were lower than those predicted by data from healthy subjects. 5. Areas under the plasma concentration-time curves of sulphadoxine after oral and i.m. administration did not differ significantly, although maximum plasma drug concentrations were higher after the i.m. route (P = 0.03). 6. The AUC values of pyrimethamine did not differ significantly between the two routes of administration. However, after i.m. administration AUC(0,24 h) values were smaller (P = 0.03), and the time to maximum plasma drug concentration (tmax) was longer (P = 0.004) than when the drug was given orally.