Lack of inhibition of the anti-malarial action of sulfadoxine-pyrimethamine by folic acid supplementation when used for intermittent preventive treatment in Gambian primigravidae.

Folic acid is frequently given to pregnant women at the same time as intermittent preventive treatment (IPTp) with sulfadoxine/pyrimethamine (SP), but it is not known if it interferes with the anti-malarial activity of SP. To investigate this concern, 1,035 Gambian primigravidae were randomized to receive either folic acid (500-1,500 microg/day) together with oral iron (522) or oral iron alone (513) for 14 days at the same time as they received IPTp with SP. On presentation, 261 women (25%) had Plasmodium falciparum asexual parasitemia. Prevalences of parasitemia on day 14 after treatment were similar in both groups: 5.7% (26 of 458) in the iron plus folic acid group and 4.9% (22 of 446) in the iron alone group (risk difference = 0.74%, 95% confidence interval [CI] = -2.2% to 3.7%). Parasitologic cure was observed in 116 (91%) of 128 of women who were parasitemic on presentation and who received iron and folic acid and in 122 (92%) of 133 women who received iron alone (difference = 1.1%, 95% CI = -5.6% to 8.0%). Women who received folic acid and iron had a slightly higher mean hemoglobin concentration at day 14 than women who had received iron alone (difference = 0.14 g/dL, 95% CI = 0.01-0.27 g/dL). The results of this study suggest that in an area of low SP resistance, administration of folic acid to pregnant women in a dose of 500-1,500 mug/day will not interfere with the protective effect of SP when used for IPTp.

Utilization of exogenous folate in the human malaria parasite Plasmodium falciparum and its critical role in antifolate drug synergy.

The antifolate combination pyrimethamine/sulphadoxine (PYR/SDX; Fansidar) is frequently used to combat chloroquine-resistant malaria. Its success depends upon pronounced synergy between the two components, which target dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) in the folate pathway. This synergy permits clearance of parasites resistant to either drug alone, but its molecular basis is still unexplained. Plasmodium falciparum can use exogenous folate, which is normally present in vivo, bypassing SDX inhibition of DHPS and, apparently, precluding synergy under these conditions. However, we have measured parasite inhibition by SDX/PYR combinations in assays in which folate levels are strictly controlled. In parasites that use exogenous folate efficiently, SDX inhibition can be restored by levels of PYR significantly lower than those required to inhibit DHFR. Isobolograms show that the degree of synergy between PYR and SDX is highly dependent upon prevailing folate concentrations and are indicative of PYR acting to block folate uptake and/or utilization. No significant synergy was observed at physiological drug levels when PYR/SDX acted on purified DHFR, whether wild type or mutant. We conclude that the primary basis for antifolate synergy in these organisms arises from PYR targeting a site (or sites) in addition to DHFR, which restores DHPS as a relevant target for SDX.

A systematic approach to the development of a rational malaria treatment policy in Zambia.

Despite the spread of chloroquine-resistant Plasmodium falciparum throughout sub-Saharan Africa, chloroquine (CQ) remains the first-line treatment for uncomplicated infection in most countries. To assess the efficacy of CQ and sulphadoxine-pyrimethamine (SP) in Zambia, studies using a standardized 14-day in vivo test were conducted at 6 geographically representative sites. Febrile children < or = 5 years of age were treated with standard doses of CQ or SP and monitored for parasitological failure (using modified WHO criteria) and clinical failure (fever with parasitaemia after completion of therapy). RII/RIII (high to moderate level) parasitological failures were identified in 34% to 70% of CQ-treated children (total N = 300) at the 6 sites and clinical failures in 31% to 48%. SP testing at 2 sites identified RII/RIII failures in 3% and 17% of children and only 1 clinical failure at each site. Because of the high levels of CQ resistance identified in these trials, the Ministry of Health of Zambia convened a national consensus meeting which recommended that Zambia's national malaria treatment policy be modified to make SP available at all health facilities for use in persons who fail initial therapy with CQ. In addition, selected sites, staff, and the methodology from these studies were used to implement a sentinel surveillance system for antimalarial drug efficacy. This systematic approach to antimalarial drug efficacy testing could be easily replicated in other countries seeking to reassess their malaria treatment policies.

Chloroquine in Africa: critical assessment and recommendations for monitoring and evaluating chloroquine therapy efficacy in sub-Saharan Africa.

Chloroquine-resistant malaria is a major public health threat in sub-Saharan Africa. While a few countries have already replaced chloroquine as the first-line therapy for uncomplicated malaria or are in the process of doing so, other countries are faced with the complicated task of assessing the current status of drug resistance, making national policy-level decisions about whether to replace chloroquine or not, and initiating a monitoring system to track changes in the efficacy of malaria therapy. There is currently no standardized approach for collecting and interpreting data on therapy efficacy. There is also no agreement as to how much chloroquine resistance or treatment failure is acceptable and how much warrants a change in treatment policy. Using data collected in 10 sites in eastern and southern Africa between 1990 and 1996, we have assessed the therapeutic response to chloroquine and investigated predictors of clinical success or failure. Based on these experiences and analyses, a standardized protocol for in vivo studies of the efficacy of malaria therapy and for approaches to designing monitoring systems are proposed. The process of making policy-level decisions based on data collected by these systems is also discussed.

[Ca++ ion transport blockers as reversants of the drug resistance of malarial parasites. 2. The effect of praziquantel on the resistance to chloroquine and compound R-70-Zh of Plasmodium berghei]. / Blokatory transporta ionov Ca++ kak reversanty lekarstvennoi ustoichivosti maliariinykh parazitov. Soobshchenie 2. Vliianie prazikvantelia na ustoichivost' k khlorokhinu i soedineniiu R-70-Zh u Plasmodium berghei.

The reversing action of anthelminthic praziquantel (P) on the effect of chloroquine (C) and compound R-70-Zh (styrylquinazoline) was revealed on a Plasmodium berghei model (white inbred mice), using a LNK65 isolate with naturally reduced sensitivity to chloroquine and its polyresistant line LNK65CHLFR with acquired resistance to chloroquine/fansidar (selected in our laboratory). P (125 mg/kg) in combination with C showed a potentiating effect not only on the LNK65 isolate, but also on the LNK65CHLFR line, while investigated separately on this line, both drugs were not effective in tested doses. Moreover, the similar effect of C on the LNK65CHLFR line was achieved in the dose that was 4 times higher than that of P/C combination. P in a standard dose on the LNK65 isolate showed a more marked activation of compound R-70-Zh that on C. The potentiating effect was manifested in combination with R-70-Zh in the dose half as high as that of C; this phenomenon was also reflected by the efficiency index (5.0 against the 4.0) accepted in our laboratory and may be associated with the higher sensitivity of the LNK65 isolate to R-70-Zh. P showed some antimalarial action which manifested itself only by morphological changes on P. berghei parasites similar to those observed under the action of some dihydropholate reductase inhibitors, such as pyrimethamine.

[Drug-resistant tropical malaria in Angola]. / Lekarstvenno-ustoichivaia tropicheskaia malariia v Angole.

Three antimalarial treatment regimens by the complete standard WHO tests were examined in 105 Plasmodium falciparum-infected patients who were nonimmune newcomers treated at the Russian hospital in Luanda in 1991-1992, 61% showed chloroquine resistance and 40% fansidar resistance. All 59 patients with high rates of parasitemia were successfully cured with quinine in combination with tetracycline. Thick, if required thin, blood smears were microscopically examined. The findings suggest that Fansidar should be a drug of first-line therapy in Angola, though in the neighbouring countries quinine continues preserving its efficacy, but there is a delayed elimination of the parasites within 7 days of initiation of the therapy, making it necessary to prolong therapy with this drug up to 10 days.

[The modelling of the multiple drug resistance of the malarial parasites. 1. The combined resistance of Plasmodium berghei to chloroquine and fansidar]. / Modelirovanie mnozhestvennoi lekarstvennoi ustoichivosti maliariinykh parazitov. Soobshchenie 1. Sochetannaia ustoichivost' Plasmodium berghei k khlorokhinu i fansidaru.

Using a recurrent technique, P. berghei isolate resistant to chloroquine-fansidar combination is formed in golden hamsters. The isolate resistant to chloroquine-fansidar combination was 4 times less sensitive to chloroquine, 2 times less sensitive to fansidar and its combinations, 2 times less sensitive to sulfadoxine, 31 times less sensitive to pyrimethamine, as compared to the baseline isolate LNK65 P. berghei characterized by naturally reduced sensitivity to chloroquine.

Optimal concentration of p-aminobenzoic acid and folic acid in the in vitro assay of antifolates against Plasmodium falciparum.

In vitro tests for Plasmodium falciparum sensitivity to pyrimethamine, sulfadoxine, and both drugs in combination were performed in four kinds of culture medium, each differing in p-amino benzoic acid (PABA) and folic acid concentrations. Results of the tests using pyrimethamine-sensitive and pyrimethamine-resistant isolates indicated that drug activity was reduced proportionally to the concentrations of these two growth factors in the medium. The optimal concentrations of PABA and folic acid for parasite growth and drug susceptibility, as evaluated by microscopic examination and by the extent of incorporation of radioactive 14C-pyrimethamine and 14C-sulfadoxine, were 10 ng/ml and 2 ng/ml, respectively. Depletion of PABA and folic acid from the medium had no effect on drug-resistant parasites but multiplication of drug-sensitive isolates was markedly reduced. Medium containing 0.5 ng/ml PABA and 10 ng/ml folic acid was the best for parasite growth regardless of the degree of drug sensitivity. Results obtained by using this medium agreed most closely with results from in vivo observations.

Antagonism of sulfadoxine and pyrimethamine antimalarial activity in vitro by p-aminobenzoic acid, p-aminobenzoylglutamic acid and folic acid.

The activity of pyrimethamine and sulfadoxine against two strains of Plasmodium falciparum has been studied in vitro by a radioisotopic technique. Low level antagonism of pyrimethamine resulted from the inclusion of p-aminobenzoic acid, p-aminobenzoylglutamic acid or folic acid in the test medium. Sulfadoxine activity was antagonised slightly by p-aminobenzoic but not by p-aminobenzoylglutamic acid, and antagonised markedly by folic acid at concentrations above 4 X 10(-8) M. At 10(-7) M folic acid, a concentration lower than that of normal RPMI medium 1640, sulfadoxine activity was reduced 7000 to 9000-fold in comparison with controls. These results are of importance in terms of the utilisation of folates by P. falciparum, the susceptibility of the parasite to antifolate drugs and the in vitro determination of parasite susceptibility.