Response of falciparum malaria in vivo to a standard regimen of chloroquine in Kisumu District, Western Kenya

The sensitivity of Plasmodium falciparum to chloroquine was studied in 140 children in two locations in Western Kenya. The standard WHO in vivo field test was used and chloroquine phosphate 25 mg base/kg administered in divided doses over three days. In one area 13.2% of cases had recrudescent parasitaemias, while in the other area 8.2% of infections were resistant, with 3.5% having an RII pattern. The remaining isolates were sensitive to chloroquine. Further in vivo and in vitro tests in the region are needed to document the extent and level of resistance.     

Clinical efficacy of mefloquine in children suffering from chloroquine-resistant Plasmodium falciparum malaria in Nigeria

One hundred and thirteen children with symptomatic uncomplicated falciparum malaria were treated with either chloroquine 25 mg/kg body weight over 3 d (51 subjects) or mefloquine 25 mg/kg body weight single dose (62 subjects). The cure rate in the chloroquine group was 65% and in the mefloquine group 100%. 14 patients with chloroquine-resistant falciparum malaria (7 RI, 6 RII and one RIII) were successfully treated with mefloquine. The clearance times of parasitaemia and fever were 60 +/- 21.5 h and 24.7 +/- 10.1 h respectively in the chloroquine-sensitive group and 52.3 +/- 18.2 h and 24.5 +/- 23.7 h respectively in the mefloquine group. In the chloroquine-resistant group treated successfully with mefloquine, these clearance times were 44.0 +/- 8.9 and 24.0 h respectively. The only remarkable adverse reaction in the chloroquine group was pruritus which occurred in 7 subjects. Abdominal pain and diarrhoea (8 subjects) and dizziness (3 subjects) were the only important adverse reactions in the mefloquine group. It is concluded that, despite previous reports of primary reduced susceptibility to mefloquine in vitro of some West African isolates of Plasmodium falciparum, this drug may be useful in the treatment of both chloroquine-sensitive and chloroquine-resistant falciparum malaria in West Africa.     

Effectiveness of amodiaquine, sulfadoxine-pyrimethamine, and combinations of these drugs for treating chloroquine-resistant falciparum malaria in Hainan Island, China

The study was carried out in 1985-86 in Hainan Island where Plasmodium falciparum is resistant to chloroquine. Fifty cases of falciparum malaria were treated with 1800 mg amodiaquine for 3 days: the cure rate was 65.3%, and the mean time to clear fever and asexual parasitaemia was 30.7 and 60.3 hours, respectively; 34.7% of cases showed RI or RII recrudescence, and one patient''s temperature did not come down to normal within 7 days.     

Plasmodium falciparum: sensitivity to chloroquine in vivo in three ecological zones in Ghana.

4690 children aged 6-15 years in 5 urban and 4 rural communities in 3 ecological zones in Ghana were screened from June 1988 to December 1990 to provide suitable candidates for the World Health Organization standard in vivo test for susceptibility of Plasmodium falciparum to chloroquine. 1880 (40.1%) had parasitaemia, mostly (83.7-98.6%) due to P. falciparum infection. Of the 626 in vivo tests performed, 570 (91.1%) showed sensitivity to chloroquine and 56 (8.9%) responses were classified as resistant to chloroquine at RI (5.1%) and RII (3.8%). The resistance responses were commonest (17.1-22.7%) in the coastal zone, followed by the savanna zone (8.6-10.0%), and lowest in the forest zone (3.1-6.3%). The RII responses occurred mainly in communities in the coastal zone. There was no RIII resistance in any zone. The pattern of RI (early) and RII responses of P. falciparum to chloroquine in this study suggested an increase in sensitivity, or a reduction in resistance, of P. falciparum to chloroquine from the coast to the forest and northern savanna zones, and from the urban to the rural communities in each zone in Ghana.     

A national survey of the prevalence of chloroquine resistant Plasmodium falciparum malaria in The Gambia

In The Gambia, 760 children less than 10 years of age with Plasmodium falciparum malaria were treated with chloroquine (25 mg/kg) and followed-up 2 and 9 d after the start of treatment. 700 children (92.1%) completed the study. The level of in vivo resistance to chloroquine varied by area from 0.4% to 16.4%. Of the 28 children found to have chloroquine resistant malaria, none was ill when seen at the 9 d follow-up and only 3 (10.3%) required further treatment with alternative antimalarials because of persistent high levels of parasitaemia. However, the fact that 30.4% of the children who completed the study had chloroquine in their urine at presentation may have masked the true level of resistance and led to underestimation of the clinical significance of these findings. The blood film at day 2 did not usefully predict resistance. 67 isolates were tested in vitro for chloroquine sensitivity. The mean EC50 was 15.5 nmol/litre, an eight-fold decrease in sensitivity from that of isolates tested in 1982. 8 (11%) of the isolates had EC50s above the WHO reference value for sensitive isolates of 18.3 nmol/litre, with values ranging from 22 to 65 nmol/litre of culture medium. Gambian isolates were sensitive to quinine (mean EC50 = 49.6 nmol/litre).     

Failure of erythromycin to improve chloroquine treatment of Plasmodium falciparum malaria in Kenya

58 children aged 1 to 10 years who had pure Plasmodium falciparum infections acquired on the coast of Kenya were treated with chloroquine 25 mg/kg given over 3 d and erythromycin 10 mg/kg 4 times a day given for 7 d. After 4 weeks follow-up, 62% had recurrent infections and 11% failed to clear their parasitaemia (1 had an RIII pattern of resistance). Of 38 children treated with chloroquine 25 mg/kg alone, 55% had recurrences and 21% failed to clear (including 1 RIII). In vitro microtests classified 74% of isolates from initial infections and 91% of isolates from recurrent infections as resistant. Erythromycin does not improve chloroquine treatment in children with infections due to P. falciparum having low to moderate levels of chloroquine resistance.     

Comparative trial of oral versus intramuscular chloroquine in children with cerebral malaria.

One hundred and thirteen children aged 12 years or less with cerebral malaria in Accra, Ghana were treated with chloroquine either with a low dose regime of 3.5 mg/kg 8-hourly intramuscularly, or orally by nasogastric tube, in a standard regime, both to a total of 25 mg/kg body weight. There was no obvious difference in outcome in the 2 treatment groups. The overall mortality of 5.3% (5.9% and 4.4% in the oral and intramuscular treatment groups respectively) was similar to that seen 10 years ago in this hospital. The average parasite clearance time had increased to 61 h, compared to 41 h noted 10 years ago. The incidence of hypoglycaemia (3%) was very low compared to studies in other malaria endemic areas. The reason for this is not clear but it could have contributed to the low mortality. Neurological deficits were seen on day 14 in 7.8% of patients. Parasitaemia recurred within 14 d in 22% of surviving patients, confirming the presence of RI/RII chloroquine resistance in Accra.     

Mutations in the pfmdr1, dhfr and dhps genes of Plasmodium falciparum are associated with in-vivo drug resistance in West Papua, Indonesia

This study (conducted in 1996-99) examines the association of mutations in pfmdr1, dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes of Plasmodium falciparum with in-vivo drug resistance in West Papua, Indonesia. Initially, 85 patients infected with P. falciparum were treated with chloroquine, of whom 21 were cleared of parasites, 49 had parasitaemias classified as RI, RII or RIII resistance and 1 patient had recrudescent parasitaemia. Fansidar (pyrimethamine-sulfadoxine) was the second-line treatment and 18 patients were cleared of parasites and 31 had continuing infections classified as RI, RII or RIII resistance and 1 patient had recrudescent parasitaemia. The pfmdr1, dhfr and dhps genes were examined for mutations previously shown to be associated with resistance to these drugs. In this study, mutations in pfmdr1 were associated with chloroquine resistance and mutations in both dhfr and dhps were associated with Fansidar resistance in vivo. Interestingly, Gly-437 in dhps along with Arg-59/Asn-108 in dhfr were associated with RI, RII and RIII resistance whereas Glu-540 was highly associated with only RII and RIII Fansidar resistance. This finding supports the hypothesis that the molecular basis of RI, RII and RIII Fansidar resistance involves an accumulation of mutations in both dhfr and dhps. These results suggest that mutations in both dhfr and dhps genes are a good predictor of potential Fansidar treatment failure.     

Response of children with Plasmodium falciparum to chloroquine and development of a national malaria treatment policy in Zaire

In vivo sensitivity of Plasmodium falciparum to chloroquine was evaluated in 4 of 9 regions of Zaire in 1985 to develop a national strategy for treatment of malaria. Children less than 5 years of age were treated with either a single dose of chloroquine base, 10 mg/kg, or a dose of 25 mg/kg given over 3 d. A modified 7-day World Health Organization in vivo test was used with follow-up 2, 3 and 7 d after the start of treatment. 339 children were studied. In Bwamanda 92% of children were aparasitaemic 7 days after chloroquine, 10 mg/kg, but in Kinshasa only 44% were free of parasites after 25 mg/kg chloroquine. The mean drop in parasite density among those who did not clear parasites by day 7 was greater than 98% of the initial value. Although the parasite density decreased markedly, the failure of most subjects to become aparasitaemic indicated a marked decrease in parasite sensitivity since 1983. Only one child of 51 who were initially febrile remained febrile, although 14 (28%) of these had resistant parasites. The decrease in parasitaemia and temperature, even among children with resistant strains, led the Ministry of Health to recommend 25 mg/kg chloroquine as first line treatment for fever/malaria in their national malaria control plan. The plan includes drug sensitivity surveillance and a referral system for patients who do not respond to chloroquine treatment.     

The changing pattern of Plasmodium falciparum susceptibility to chloroquine but not to mefloquine in a mesoendemic area of Somalia

The response of Plasmodium falciparum to chloroquine and mefloquine was investigated in a mesoendemic area of Somalia from 1986 to 1989. Serial in vivo field tests for chloroquine sensitivity were performed and the sensitivity in vitro to chloroquine and mefloquine was evaluated using the standard WHO in vitro microtest. Chloroquine treatment in vivo (25 mg base/kg body weight) resulted in parasite clearance in all patients within 7 d (S/RI) in 1986, while 17%, 19% and 30% RII/RIII responses were found in 1987, 1988 and 1989 respectively. There was consistent increase of parasite clearance time of the S/RI cases in all years. The sensitivity study in vitro in 1986 showed a low degree of chloroquine resistance in 3 of 29 isolates tested and a mean 50% effective dose (EC50) and EC99 of 0.34 x 10(-6) M and 1.99 x 10(-6) M, respectively. In contrast, in 1989, 12 of the 19 isolates tested were resistant to chloroquine. The mean EC50 and EC99 values had increased to 0.78 x 10(-6) M and 7.50 x 10(-6) M respectively. The data in vivo and in vitro indicate a rapid increase of chloroquine resistance both in frequency and degree. All isolates tested in 1986 and 1989 were fully inhibited by mefloquine at 3.2 x 10(-6) M, suggesting full sensitivity. Thus, increased resistance of P. falciparum to chloroquine did not significantly influence the sensitivity pattern of mefloquine.     

Chloroquine resistant Plasmodium falciparum in indigenous residents of Cameroon

Thirty-nine percent (36 of 92) of children in Limbe, Cameroon, treated with chloroquine (10 mg/kg body weight on days 1 and 2, and 5 mg/kg on day 3) for falciparum malaria failed to respond within 7 d of treatment. Twenty-two of these children with chloroquine-resistant malaria were successfully treated with Fansidar [one-half tablet (250 mg sulfadoxine and 25 mg pyrimethamine) per 10 kg body weight], while the other 14 children were cured with mefloquine (25 mg/kg body weight). In vitro, a combination of verapamil at 1.0 x 10(-6) M with chloroquine or desethylchloroquine reversed resistance to the antimalarial drug and its primary metabolite in each of the 2 isolates successfully adapted and maintained in continuous culture. Similar combinations had no effect on susceptibilities of a sensitive reference clone, D6, used as control. Both chloroquine-resistant isolates from Cameroon were significantly more susceptible to mefloquine and halofantrine in vitro than the chloroquine-sensitive reference clone. Clinical observation, and in vitro confirmation, of chloroquine-resistant falciparum malaria in these indigenous children from Cameroon, and the current socio-economic condition in West Africa, underscore the need for pragmatic health management policies for efficient use of alternative antimalarial drugs in controlling drug resistant Plasmodium falciparum in the region. This observation of reversal of chloroquine resistance in isolates of P. falciparum obtained from West Africa, and a previous report on clones obtained from south-east Asia and South America, suggest that the mechanism(s) of resistance to chloroquine may be identical in resistant parasites from the 3 continents.     

Failure of large-dose erythromycin in combination with a standard dose of chloroquine or quinine in the treatment of human falciparum malaria

In eastern Thailand, falciparum malaria is highly chloroquine-resistant and is quickly becoming quinine-resistant. In the present study, ten patients with falciparum malaria were given large doses of erythromycin, combined with standard doses of chloroquine; the cure rate was 0 out of 10 (4 RIII failures, 6 RII failures). A further ten patients were given erythromycin with standard doses of quinine; 2 of the 10 patients were cured (8 RI failures). These regimens thus appear to have no appreciable effect against falciparum infections in eastern Thailand.     

Studies of resistance to chloroquine, quinine, amodiaquine and mefloquine among Philippine strains of Plasmodium falciparum

One hundred cases of slide-confirmed Plasmodium falciparum malaria admitted to the San Lazaro Hospital, Manila, Philippines were screened for in vitro resistance to chloroquine, quinine, amodiaquine and mefloquine using the microtechnique. 59 of the 100 primary parasite isolates produced schizonts, whereas the remaining 41 isolates did not. 51 of the 59 isolates tested were resistant in vitro to chloroquine and eight were sensitive. In contrast, three of the primary isolates were resistant to quinine, three showed resistance to amodiaquine and four were mefloquine-resistant. 43 of the strains judged chloroquine-resistant in vitro were fully in vitro sensitive to amodiaquine, quinine and mefloquine. One chloroquine-resistant isolate was also resistant to quinine alone. Three isolates that were resistant to chloroquine were also resistant to amodiaquine. An additional three were cross-resistant to chloroquine and mefloquine. A single isolate was found to be resistant to chloroquine, quinine and mefloquine and another was cross-resistant to chloroquine, quinine and amodiaquine. All strains demonstrating in vitro resistance to amodiaquine, quinine or mefloquine also showed in vitro resistance to chloroquine. The parasites in 22 patients showed in vivo resistance to chloroquine therapy. 86% were of the R1 type, 9% were R2 and 5% R3. All 22 patients demonstrating in vivo resistance to chloroquine showed in vitro resistance.     

Therapeutic efficacy of chloroquine and sulfadoxine/pyrimethamine against Plasmodium falciparum infection in Somalia

OBJECTIVE: To assess the efficacy of chloroquine and sulfadoxine/pyrimethamine in the treatment of uncomplicated Plasmodium falciparum infections in Somalia. METHODS: Patients with clinical malaria in Merca, an area of high transmission of the disease, were treated with the standard regimens of chloroquine (25 mg/kg) or sulfadoxine/pyrimethamine (25 mg sulfadoxine and 1.25 mg pyrimethamine per kg). Similar patients in Gabiley, an area of low transmission, received the standard regimen of chloroquine. The clinical and parasitological responses were monitored for 14 days. FINDINGS: Chloroquine treatment resulted in clinical failure in 33% (n = 60) and 51% (n = 49) of the patients in Merca and Gabiley respectively. There were corresponding parasitological failures of 77% RII/RIII and 35% RII/RIII. Patients who experienced clinical failure had significantly higher initial parasitaemia than those in whom there was an adequate clinical response, both in Merca (t = 2.2; P t = 2.8; P n = 50) of the patients achieved an adequate clinical response despite a parasitological failure rate of 76% RII/RIII. CONCLUSION: Chloroquine should no longer be considered adequate for treating clinical falciparum malaria in vulnerable groups in the areas studied. Doubts about the therapeutic life of sulfadoxine/pyrimethamine in relation to malaria are raised by the high levels of resistance in the Merca area and underline the need to identify suitable alternatives.     

Efficacy of a 3-day oral regimen of a quinine-quinidine-cinchonine association (Quinimax) for treatment of falciparum malaria in Madagascar

In the search for an effective, safe and field-adapted alternative to chloroquine for therapy of chloroquine-resistant Plasmodium falciparum infections in Africa, a 3-d oral regimen of Quinimax (an association of quinine, quinidine and cinchonine) was evaluated in 35 individuals with P. falciparum in Madagascar, an area with chloroquine resistance. 63% of the parasite strains isolated were resistant in vitro to chloroquine, and 59% of the infections were present despite previous chloroquine intake. Three daily oral doses of 10 mg/kg Quinimax for 3 d cleared parasitaemia and improved clinical status in all subjects. Mean parasite and fever clearance times were 51.7 and 37.4 h, respectively. All patients were aparasitaemic at the end of the 7-d follow-up. When formulating therapy guidelines, the 3-d Quinimax regimen should be considered as a valuable alternative to chloroquine for treating falciparum malaria in African areas with clinical resistance to chloroquine.     

Limits of the efficacy of chloroquine and sulfadoxine-pyrimethamine in Northern Abidjan (Cote d'Ivoire): Combined in vivo and in vitro studies

Antimalarial drug resistance in endemic malaria zones is first detected in vitro; when it reaches a certain threshold, it becomes perceptible and is expressed in therapeutic failure among subjects only slightly or not at all immune. This work conducted in northern Abidjan (Cote d'Ivoire) studied children with uncomplicated malaria, who were followed for 14 days (during the year 2000) in accordance with the WHO protocol for surveillance of antimalarial drug resistance. Concomitantly, the Plasmodium falciparum isolates were cultured in the presence of variable concentrations of chloroquine, pyrimethamine and quinine during in vitro chemosensitivity tests. The RPMI 1640 used as medium for the pyrimethamine did not contain PABA (para-amino benzoic acid) or folic acid. In all, 114 in vitro tests were completed, 33 to chloroquine, 32 to pyrimethamine, and 49 to quinine. Therapeutic efficacy was tested in 65 patients: 33 to chloroquine and 32 to sulfadoxine-pyrimethamine (SP). The results found 36% of the isolates were chloroquine-resistant (CQ-R) and 33% of the patients treated with chloroquine did not respond adequately (therapeutic failure, TF). The 12 CQ-R isolates corresponded to 11 TF subjects and 1 patient with adequate clinical and parasitological response. The concordance between the two tests was good (kappa=0.93). For pyrimethamine, 37.5% of the isolates were resistant (PYR-R), and 37.5% of patients responded adequately to SP. The 12 PYR-R isolates were from 12 TF subjects, so that kappa=1.0, when pyrimethamine resistance is defined as IC50 > 2,000 nM. Because of the elevated rate of chloroquine resistance, the national antimalaria program has recommended since July 2003 that amodiaquine be used as a first-line drug, to replace chloroquine. The relatively elevated number of TF with SP are a source of concern, because it is used in Yopougon (Abidjan). Additional studies to assess the prevalence of resistance to this combination in other areas of Abidjan city (Cote d' Ivoire) would be useful.     

In vitro sensitivity of southern African reference isolates of Plasmodium falciparum to chloroquine and pyrimethamine.

The in vitro sensitivity to chloroquine and pyrimethamine of 19 culture-adapted southern African reference isolates of Plasmodium falciparum was determined using a 48-hour assay. Four isolates collected in KwaZulu, Natal, were sensitive to chloroquine, and one of these was sensitive to the drug in vivo. Eight isolates from KwaZulu or Mozambique were resistant to chloroquine in vitro. Six of these isolates were chloroquine-resistant in varying degrees in vivo. Four of five isolates from north-eastern Transvaal and two clinically chloroquine-resistant Malawian isolates were resistant to chloroquine in vitro. A wide range of pyrimethamine susceptibilities was detected (0.01 mumol/l to greater than 3.0 mumol/l), although most isolates were inhibited at 0.1 mumol/l, indicating a low level of resistance. These results confirm the presence of both chloroquine and pyrimethamine resistance in the endemic areas of South Africa. This has serious implications for the prophylaxis and treatment of P. falciparum malaria in South Africa.     

A molecular surveillance system for global patterns of drug resistance in imported malaria

Analysis of imported malaria in travelers may represent a novel surveillance system for drug-resistant malaria. We analyzed consecutive falciparum malaria isolates from Canadian travelers from 1994 to 2000, for polymorphisms in pfcrt, dhfr, and dhps linked to chloroquine and pyrimethamine/sulfadoxine resistance. Forty percent of isolates possessed the K76 pfcrt allele, suggesting that many imported falciparum infections are still responsive to chloroquine. Travelers who had recently taken chloroquine had a significantly increased risk of harboring isolates with pfcrt resistance alleles (odds ratio = 4.47; p=0.03). The presence of two or more mutations in dhfr or dhps was found in 64.8% (95% confidence interval [CI] 54.6 to 73.9) and in 30.4% (95% CI 21.7 to 40.3) of isolates, respectively, and increased significantly over the course of the study. These molecular markers indicate that pyrimethamine/sulfadoxine resistance is increasing and is now too high to rely on this drug as a routine therapeutic agent to treat malaria in travelers.     

Chloroquine, sulfadoxine-pyrimethamine and amodiaquine efficacy for the treatment of uncomplicated Plasmodium falciparum malaria in Upper Nile, south Sudan

The current first-line and second-line drugs for Plasmodium falciparum malaria in South Sudan, chloroquine and sulfadoxine-pyrimethamine (SP), were evaluated and compared with amodiaquine, in an MSF-Holland-run clinic in eastern Upper Nile, South Sudan from June to December 2001. Patients with uncomplicated malaria and fever were stratified by age group and randomly allocated to one of 3 treatment regimes. A total of 342 patients was admitted and followed for 14 d after treatment. The dropout rate was 10.2%. Of those who completed the study, 104 were treated with chloroquine (25 mg/kg, 3 d), 102 with SP (25 mg/kg sulfadoxine and 1.25 mg/kg pyrimethamine, single dose) and 101 with amodiaquine (25 mg/kg, 3 d). Adequate clinical response was observed in 88.5% of patients treated with chloroquine, 100% of patients treated with SP and 94.1% of patients treated with amodiaquine. In children aged < 5 years, the success rate was lower: 83.3% for chloroquine and 93.0% for amodiaquine. In adults no treatment failures were found, but children aged 5-15 years showed intermediate levels. In addition, we determined the initial genotypes of dhfr and dhps of 44 isolates from the SP-treated group and > 80% were found to be wild type for dhfr and 100% for dhps. Two percent of isolates had a single mutation and 16% had double mutations of dhfr. These data are in full agreement with the clinical effectiveness of SP. A change in malaria treatment protocols for South Sudan is recommended.     

The relationship between the response of Plasmodium falciparum malaria to mefloquine in African children and its sensitivity in vitro.

The clinical efficacy of two doses of mefloquine (15 and 25 mg/kg body weight) was evaluated in 85 children suffering from acute symptomatic falciparum malaria. The cure rate on day 28 was 100% in both groups. There was no significant difference (P > 0.05) in the mean parasite and fever clearance times in both groups (48.5 +/- 14.6 and 32.0 +/- 12.7 h respectively for the 25 mg/kg group and 49.0 +/- 15.1 and 30.0 +/- 13.3 h respectively for the 15 mg/kg group). There was also no significant difference (P > 0.05) in these values between children with hyperparasitaemia (53.6 +/- 11.1 and 36.0 +/- 17.0 h respectively) and those without hyperparasitaemia (49.1 +/- 13.6 and 31.8 +/- 14.6 h respectively). Recurrence of parasitaemia was observed after day 30 in 2 patients in the 15 mg/kg group and in 1 patient in the 25 mg/kg group. In vitro, 3 of 21 isolates showed reduced susceptibility to mefloquine, with minimum inhibitory concentrations (MIC) > 67 nM/litre. The MIC and 50%, 90% and 99% inhibitory concentrations were 200.8, 6.27, 31.7 and 119.6 nM/litre respectively. Four of 22 isolates were resistant to chloroquine (MIC > 108 nM/litre). Isolates that showed low sensitivity to mefloquine in vitro were sensitive to chloroquine in vitro, and the 4 that were resistant to chloroquine were sensitive to mefloquine. Irrespective of MIC and dose of mefloquine, parasitaemia cleared in all subjects in 96 h or less.(ABSTRACT TRUNCATED AT 250 WORDS)