Qinghaosu resistance in rodent malaria

Resistance to qinghaosu (artemisinin) developed rapidly in a chloroquine-resistant line of Plasmodium yoelii (NS) passaged in mice, but was not produced in chloroquine-sensitive P. berghei. Development of resistance took place in an apparently stepwise fashion. After removal of drug selection pressure some resistance was lost which was regained rapidly within three passages when drug pressure was reapplied. The resistant QS line was cross-resistant to two reduced derivatives of artemisinin but not to propoxycarbonyl dihydroartemisinin or artesunate. No significant resistance was shown against primaquine, pyrimethamine, cycloguanil or pyrimethamine-sulphadoxine, but resistance to chloroquine was enhanced and marked resistance to quinine, mefloquine and amodiaquine was noted. It is suggested that the unusual cross-resistance pattern of the strain relates to changes in membrane characteristics.     

Chemosuppression of malaria by the triple combination mefloquine/sulfadoxine/pyrimethamine: a field trial in an endemic area in Malaysia

Malaria, particularly that due to chloroquine-resistant Plasmodium falciparum, which requires management with antimalarial drugs capable of protecting against multiresistant strains, has emerged in Malaysia. A study was carried out to assess the efficacy and tolerability of 2 dosages of mefloquine/sulfadoxine/pyrimethamine (MSP; RO 13-5112) compared to Fansidar in a malaria endemic area. 914 subjects in 3 random groups were studied. Occurrence of malaria was assessed both clinically as well as by blood films. Plasma drug levels were also measured. The results showed that the low dose of MSP was completely effective in suppressing parasitaemia. 2.7% of the study population reported adverse drug reactions, the lowest incidence being in subjects on the low dose; their blood chemical profiles were also the least affected. The plasma levels of pyrimethamine and sulfadoxine achieved in the low dose group were slightly higher than expected, but there was no significant difference in bioavailability. The study showed that, for chemoprophylaxis, a low dose of MSP provided effective protection with minimal side effects.     

Plasma concentrations of sulfadoxine-pyrimethamine and of mefloquine during regular long term malaria prophylaxis

The plasma concentrations of sulfadoxine, pyrimethamine, mefloquine and its major metabolite were determined in 18 healthy male volunteers who had regularly taken either 500 mg of sulfadoxine and 25 mg of pyrimethamine (Fansidar) weekly or 250 mg mefloquine regularly every 14 d during 6 months for malaria prophylaxis. The mean trough concentrations of sulfadoxine, pyrimethamine and mefloquine were 194, 0.28 and 1.48 mumol/litre and the mean half lives were 7.7, 4.2 and 25 d respectively. The variation in area under the curve for the 3 drugs was only 2-3 fold. The findings do not indicate that drug accumulation or induction of metabolism occurred during long-term usage.     

A simple technique for the detection of anti-malarial drug formulations and their presence in human urine

A simple, sensitive, specific assay technique for the detection and semi-quantification of chloroquine, amodiaquine, quinine, primaquine, sulfadoxine and pyrimethamine in formulations and in human urine by using thin layer chromatography (TLC) was developed and tested in the laboratory. The method involved developing test samples spotted on TLC chromatogram by diethylamine-toluene-isopropanol (1:4:5 v/v/v) as the eluting solvent. The solvent system diethylamine-toluene-isopropanol (1:4:5 v/v/v) enabled the elution and detection of all the tested antimalarial drugs in solution and those spiked in human urine. Detection limits for chloroquine, amodiaquine, quinine and primaquine were the lowest at 0.00025 mg/ml. Sulfadoxine exhibited a detection limit of 0.0005 mg/ml whereas that of pyrimethamine was 0.001 mg/ml. The results indicate the suitability of this technique in antimalarial drug quality and bioavailability studies. It is envisaged that this technique will adequately address the role of drug absorption and excretion in the chemotherapy of malaria as well as to detect types of antimalarial drugs commonly used in the community.     

A phase I clinical trial of Fansimef (mefloquine plus sulfadoxine-pyrimethamine) in Brazilian male subjects

A double-blind, randomized phase I clinical trial was carried out to compare Fansimef (a fixed-dose combination of mefloquine, sulfadoxine, and pyrimethamine) with sulfadoxine and pyrimethamine (Fansidar) for safety and tolerance. Twenty adult male Brazilian subjects from malaria endemic areas were studied for a period of 66 days, which included 2 days before and 63 days after drug administration.     

Prospective double-blind trial of two different doses of mefloquine plus pyrimethamine-sulfadoxine compared with pyrimethamine-sulfadoxine alone in the treatment of falciparum malaria

This double-blind study is based on the treatment of 75 adult male patients suffering from Plasmodium falciparum malaria in Medellín, Colombia, a city in which there is no malaria transmission. The patients, who came from regions with high resistance to antimalarials, were divided into three groups receiving single-dose treatment as follows: a combination of 280 mg mefloquine, 800 mg sulfadoxine and 40 mg pyrimethamine; a combination of 420 mg mefloquine, 1200 mg sulfadoxine and 60 mg pyrimethamine; and a combination of 1500 mg sulfadoxine and 75 mg pyrimethamine. After treatment, follow-up examination was performed daily for I week and then weekly for another 3 weeks. The cure rate in the mefloquine groups (within the study period of 28 days) was 100%, and in the third group 75%. Normal blood levels of the administered drugs were found in 6 patients of the third group who were not cured; they were subsequently cured with a single dose of 1000 mg of mefloquine. Drug tolerance was good and no toxic effects were demonstrated in blood and urine examinations. While the doses in the drug combinations (containing mefloquine) gave very good results, we would recommend a slightly higher dose combination of mefloquine with sulfadoxine—pyrimethamine for the treatment of falciparum malaria in areas with a high prevalence of chloroquine resistance.     

Synergistic antimalarial activity of dapsone/dihydrofolate reductase inhibitors and the interaction of antifol, antipyrimidine and antipurine combinations against Plasmodium falciparum in vitro

Using low folate, low p-aminobenzoic acid medium, 2 isolates of Plasmodium falciparum were tested in vitro against a wide range of antimetabolite compounds with known or potential antimalarial activity. ID50 values (the concentration of compound causing 50% inhibition of [3H]hypoxanthine incorporation) were determined for each compound against both isolates. The compounds tested may affect folate, pyrimidine or purine metabolism in malaria parasites and various combinations of compounds were examined for further synergistic antimalarial effects. The combination of any of the dihydrofolate reductase inhibitors cycloguanil, pyrimethamine or WR 99210 with the sulphone drug dapsone demonstrated strongly synergistic antimalarial activity. Combinations of dihydrofolate reductase inhibitors with the antipyrimidine compounds pyrazofurin or menoctone, or with the antipurine compounds tubercidin, bredinin or hadacidin, or with primaquine, failed to demonstrate synergistic activity. Most combinations of an antipurine with an antipyrimidine compound also failed to show any synergistic effect. However, weak synergism was consistently seen in the tubercidin/pyrazofurin and tubercidin/menoctone combinations. Over the 48 h intraerythrocytic cycle using tightly synchronized parasites, tubercidin demonstrated both a cytotoxic and a cytostatic effect.     

The effect of artesunate combined with standard antimalarials against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum in vitro

The interactions of artesunate with chloroquine, mefloquine, quinine, doxycycline and pyrimethamine were tested in vitro against chloroquine-sensitive (D10) and chloroquine-resistant (RSA11) strains of Plasmodium falciparum. Mefloquine and quinine both showed synergism of artesunate activity against each of the strains, whilst doxycycline showed an additive interaction. Pyrimethamine combinations were antagonistic, and the combination of artesunate with chloroquine was antagonistic against RSA11, and additive against D10. Although weak antagonism in vitro might not indicate any clinical significance, synergism with artesunate may increase the clinical usefulness of either drug, and could potentially be of value in delaying the emergence of resistance.     

In vitro drug sensitivity of Plasmodium falciparum in Acre, Brazil

In Acre, the westernmost state of Brazil in the Amazon region, the sensitivity of Plasmodium falciparum to chloroquine, amodiaquine, mefloquine, quinine and sulfadoxine/pyrimethamine was determined in vitro by the Rieckmann microtechnique. The study was performed between January and June 1987; the in vitro parasite responses to all antimalarial drugs were determined according to the recommendations of WHO. Of 83 isolates of P. falciparum, all were sensitive to mefloquine and of 87 isolates of P. falciparum, 84 (97%) were sensitive to quinine. The EC50 for mefloquine was 0.27 mumol/l and for quinine 4.60 mumol/l. In contrast, 65 of 89 (73%) and 70 of 83 (84%) isolates were resistant to amodiaquine and chloroquine, respectively; 11 isolates even grew at 6.4 mumol chloroquine/l. The EC50 for amodiaquine was 0.34 mumol/l and for chloroquine 0.73 mumol/l. Sulfadoxine/pyrimethamine resistance was seen in 23 of 25 (92%) cases. These data clearly indicate that in the western part of the Amazon region the 4-aminoquinolines, as well as sulfadoxine/pyrimethamine, can no longer be recommended for the treatment of P. falciparum infections.     

Antimalarial drugs and human neutrophil oxidative metabolism

The effect of several commonly used antimalarial drugs on human peripheral blood neutrophil oxidative metabolism was studied. The following drugs were tested: chloroquine diphosphate, quinine HCl, mefloquine, proguanil HCl, cycloguanil, pyrimethamine, sulphadoxine, and tetracycline HCl. It was found that none of the antimalarial drugs examined, at clinically obtainable concentrations, had any inhibitory effect on neutrophil oxygen consumption, glucose oxidation, superoxide production, NBT reduction, and chemiluminescence. However, at higher concentrations chloroquine, quinine, mefloquine, and proguanil inhibited neutrophil oxidative burst. There was a slight enhancing effect on neutrophil oxidative metabolism by pyrimethamine, combination of pyrimethamine-sulphadoxine, cycloguanil and tetracycline at concentrations lower than the clinical levels.     

Pharmacokinetics of mefloquine in combination with sulfadoxine-pyrimethamine and primaquine in male Thai patients with falciparum malaria

The pharmacokinetics of mefloquine (M) were studied in 59 male Thai patients with falciparum malaria. Mefloquine was administered alone (750 mg orally; group 1), or with primaquine (PQ, 45 mg; group 2), or in combination with sulfadoxine (1.5 g) + pyrimethamine (75 mg) (MSP; group 3), or as MSP + PQ (group 4). All patients in groups 1, 2 and 4 initially responded to treatment, but two patients from group 1 had RI recrudescent infections. One patient in group 3 failed to respond to treatment and was considered to have RII resistance, while a further patient from this group had RI recrudescence. The pharmacokinetic parameters for group 1 and group 3 were not significantly different. Co-administration of primaquine alone had no significant effect on the pharmacokinetics of mefloquine, but there was a statistically significant decrease in the terminal elimination half-life of mefloquine for group 4 relative to that for group 3.     

Tolerance of mefloquine alone and in combination with sulfadoxine-pyrimethamine in the prophylaxis of malaria

A randomized double blind study was performed to evaluate the tolerance and the acceptance of mefloquine alone (Lariam) compared to a combined drug regimen consisting of mefloquine, sulfadoxine and pyrimethamine (MSP; Fansimef) in the prophylaxis of malaria. 175 Europeans travelling to different malaria endemic areas received either mefloquine alone (250 mg/week) or its combination with sulfadoxine (500 mg/week) plus pyrimethamine (25 mg/week). One person taking mefloquine and two taking MSP discontinued the drug intake because of moderate clinical side effects. Mild and moderate adverse clinical reactions predominantly concerning the gastro-intestinal tract and the autonomous nervous system were reported with a significantly higher occurrence in the MSP group. With both prophylactic regimens, reversibly elevated liver enzyme activities (glutamate oxalate transaminase and glutamate pyruvate transaminase [GPT]) were observed after prophylaxis. The increase of GPT serum activity correlated significantly with relatively high GPT levels before prophylaxis in both groups. This finding suggests a limited use of both regimens in cases of liver dysfunction. One case of mefloquine-resistant Plasmodium falciparum malaria was observed from West Africa; this patient was cured by a standard regimen of chloroquine.     

Gametocytocidal and sporontocidal effects of primaquine and of sulfadiazine with pyrimethamine in a chloroquine-resistant strain of Plasmodium falciparum

Studies with 3 volunteers were conducted to determine the effects of a combination of sulfadiazine and pyrimethamine and the effects of primaquine upon mature gametocytes of a strain of chloroquine-resistant Plasmodium falciparum—the Malayan (Camp.) strain. One volunteer was treated with sulfadiazine and pyrimethamine; two other volunteers each received a single dose of 45 mg of primaquine base. The combination of sulfadiazine and pyrimethamine, although active against blood schizonts, did not exert a marked sporontocidal effect against the Malayan (Camp.) strain. In sharp contrast, primaquine, although not effective as a blood schizontocide, exerted a marked gametocytocidal and sporontocidal effect against this strain.     

A phase I clinical trial of mefloquine in Brazilian male subjects

A double-blind, randomized phase I clinical trial was carried out to compare mefloquine with sulfadoxine—pyrimethamine for safety and tolerance. Twenty adult male Brazilian subjects from areas endemic for malaria were studied for a period of 66 days, which included 2 days of basal studies and a 63-day follow-up after drug administration. Subjects received either mefloquine, given as a single oral dose of 1000 mg (4 × 250-mg tablets) or sulfadoxine—pyrimethamine (2 tablets, each containing 500 mg of sulfadoxine plus 25 mg of pyrimethamine). Clinical examination, electrocardiogram, chest X-ray, and haematological, biochemical, stool, and urine analyses were carried out before drug administration and at various intervals afterwards. Peripheral blood smears were examined for malarial parasites.     

Double-blind dose finding study of mefloquine-sulfadoxine-pyrimethamine in children with acute falciparum malaria

Three different doses of a combination of mefloquine-sulfadoxine-pyrimethamine (MSP), given double-blind as a single dose to 60 children, were evaluated for efficacy and tolerance. The children, 42 boys and 18 girls aged between 5 and 15 years, received a mefloquine dose equivalent to 1, 1.5, or 2 standard MSP (Fansimef) tablets. Radical cure was obtained in all patients with only mild to moderate side effects of nausea and vomiting, which were not worse in the higher dose groups. For children living in an endemic malarious area, a single dose of mefloquine 7.1-12.5 mg/kg, given in combination with sulfadoxine (14.3-25.0 mg/kg) and pyrimethamine (0.7-1.3 mg/kg), is a safe and effective treatment for uncomplicated chloroquine-resistant Plasmodium falciparum malaria. This dose of MSP is approximately 10 mg/kg, 20 mg/kg and 1.0 mg/kg respectively of mefloquine, sulfadoxine and pyrimethamine, which is equivalent to a single standard tablet of Fansimef (mefloquine, 250 mg; sulfadoxine, 500 mg; pyrimethamine, 25 mg) given to a child weighing 20-30 kg.     

Sensitivity of Plasmodium falciparum to chloroquine and sulfadoxine/pyrimethamine in Nigerian children

The in vivo sensitivity of Plasmodium falciparum to chloroquine and sulfadoxine/pyrimethamine was evaluated in children under 5 years of age in two areas of southern Nigeria in 1987. A modification of the WHO Standard Field and Extended Tests (in vivo) was used, with follow-up on days, 2, 3, 7, and 14 after treatment with 25 mg chloroquine per kg body weight given over 3 days, or with standard doses of sulfadoxine/pyrimethamine. Clinical and parasitological evaluations were performed. At Igbo Ora, in Oyo State, where by day 7 chloroquine was clinically successful in 94.4% of 36 children and sulfadoxine/pyrimethamine in 91.7% of 36 children, there were no parasitological failures in either treatment group. Fever regressed significantly more rapidly with chloroquine than with sulfadoxine/pyrimethamine. At Oban, in Cross River State, initial parasite densities decreased markedly with the chloroquine regimen but 63.6% of 44 children were parasitological failures on days 3, 7, or 14; and all of the 26 children who failed parasitologically and completed follow-up were successfully treated with sulfadoxine/pyrimethamine. By day 7, clinical success was demonstrated for 77.3% of the children treated with chloroquine. The in vitro sensitivity to chloroquine, quinine, and mefloquine at Igbo Ora indicated that isolates of P. falciparum were sensitive to chloroquine and quinine, but had reduced sensitivity to mefloquine. Because of its continued clinical efficacy, chloroquine remains the recommended treatment for children with uncomplicated malaria in Nigeria. Health providers are, however, encouraged to maintain supplies of sulfadoxine/pyrimethamine as an alternative and to refer patients promptly if necessary.     

Phagocytosis and bactericidal activity of human leucocytes under influence of antimalarial drugs

The phagocytic and bactericidal activity of human peripheral blood leucocytes under the influence of commonly used antimalarial drugs was studied. The following drugs were used: chloroquine diphosphate, quinine HCl, mefloquine HCl, proguanil HCl, cycloguanil, pyrimethamine and tetracycline HCl. It was found that leucocytes treated with mefloquine, proguanil and cycloguanil at concentrations higher than 0.5 mg/litre showed reduced phagocytic activity against Staphylococcus aureus. None of the other drugs tested had any inhibitory effect on phagocytosis. The bactericidal ability of the leucocytes was not affected by any of the drugs. It is concluded that none of the commonly used antimalarial drugs, at concentrations obtainable in malaria prophylaxis and therapy, have any undesirable effect on the bactericidal activity of human leucocytes.     

An integrated assessment of the clinical safety of artemether-lumefantrine: a new oral fixed-dose combination antimalarial drug

Artemether-lumefantrine (A-L), a new fixed-dose oral antimalarial drug, combines the fast onset of action of artemether (an artemisinin derivative) in terms of parasite clearance with the high cure rate of lumefantrine in the treatment of acute uncomplicated Plasmodium falciparum malaria. The extensive clinical trial database of A-L has allowed a comprehensive evaluation of its tolerability and safety in a total of 1869 patients (including 243 children aged 5-12 years and 368 children aged < 5 years). The most commonly reported and possibly related adverse effects following A-L therapy involved the gastro-intestinal (abdominal pain, anorexia, nausea, vomiting, diarrhoea) and central nervous (headache, dizziness) systems. Pruritus and rash were reported by < 2% of patients. More than 90% of the reported adverse events, many of which overlapped considerably with the clinical symptomatology or evolution of acute malaria, were rated mild to moderate in intensity. Compared to A-L, significantly higher incidences of vomiting and pruritus were observed with chloroquine, dizziness, nausea and vomiting with mefloquine, somnolence with pyrimethamine + sulfadoxine, and vomiting and dizziness with quinine. There were no serious or persistent neurological side-effects related to A-L administration. A-L did not lead to any clinically relevant alterations of the laboratory parameters. Serial electrocardiographic data were available for 713 patients. The frequency of QT interval prolongations was similar to or lower than that observed with chloroquine, mefloquine, or artesunate + mefloquine; these changes were considerably less frequent than with quinine or halofantrine. All patients with QT prolongation remained asymptomatic and no adverse clinical cardiac events were reported. Artemether-lumefantrine can thus be expected to show, both in children and in adults, a favourable safety profile for the treatment of acute, uncomplicated, P. falciparum malaria; it could as well be a reserve treatment option for travellers to endemic countries.     

Susceptibility of Plasmodium falciparum in vitro to chloroquine, mefloquine, quinine and sulfadoxine/pyrimethamine in Somalia: relationships between the responses to the different drugs.

The susceptibilities of Plasmodium falciparum to chloroquine, mefloquine, quinine and sulfadoxine/pyrimethamine were investigated in Mogadishu in 1988, after chloroquine resistance had spread widely in Somalia. Possible correlations of the responses to these drugs were also investigated. Standard World Health Organization in vitro micro-tests were performed. Of 76 isolates tested for chloroquine susceptibility, 58 (76%) were resistant to the drug with mean EC50 and EC99 values of 1.06 x 10(-6) mol/litre and 10.44 x 10(-6) mol/litre of blood, respectively, indicating a high prevalence and degree of resistance. In contrast, all isolates tested were inhibited by mefloquine 3.2 x 10(-6) mol/litre of blood, quinine at 2.56 x (-6) mol/litre of blood-medium mixture, and sulfadoxine/pyrimethamine at 6.0/0.075 x 10(-6) mol/litre of blood-medium mixture, indicating full sensitivity to these 3 drugs. However, a significant positive correlation was found between responses to quinine and chloroquine and between those to quinine and mefloquine; the responses to chloroquine and mefloquine were not correlated. The results may suggest that sites responsible for the correlation are shared between quinine and chloroquine but not essentially between chloroquine and mefloquine. Thus the evolution of chloroquine resistance together with increased use of quinine treatment of P. falciparum may increase the risks of development of quinine resistance, whereas the development of mefloquine resistance would not be triggered by chloroquine resistance.     

Single-dose therapy of falciparum malaria with mefloquine or pyrimethamine-sulfadoxine.

A single oral dose (1.5 g) of mefloquine hydrochloride cured all of 37 patients with falciparum malaria, and a single dose of pyrimethamine (75 mg) plus sulfadoxine (1.5 g) cured 34 of 38 patients. The rates at which parasitaemia and fever abated were similar for the two regimens but mefloquine was associated with a higher incidence of gastrointestinal side effects.