A trial of proguanil-dapsone in comparison with sulfadoxine-pyrimethamine for the clearance of Plasmodium falciparum infections in Tanzania

Geographic distribution of amino acid mutations in DHFR and DHPS in Plasmodium vivax isolates from Lao PDR, India and Colombia

Background

Non-synonymous mutations in dhfr and dhps genes in Plasmodium vivax are associated with sulfadoxine–pyrimethamine (SP) resistance. The present study aimed to assess the prevalence of point mutations in P. vivax dhfr (pvdhfr) and P. vivax dhps (pvdhps) genes in three countries: Lao PDR, India and Colombia.

Methods

Samples from 203 microscopically diagnosed vivax malaria were collected from the three countries. Five codons at positions 13, 57, 58, 61, and 117 of pvdhfr and two codons at positions 383 and 553 of pvdhps were examined by polymerase chain reaction-restriction fragment length polymorphism methodology.

Results

The largest number of 58R/117 N double mutations in pvdhfr was observed in Colombia (94.3 %), while the corresponding wild-type amino acids were found at high frequencies in Lao PDR during 2001–2004 (57.8 %). Size polymorphism analysis of the tandem repeats within pvdhfr revealed that 74.3 % of all the isolates carried the type B variant. Eighty-nine per cent of all the isolates examined carried wild-type pvdhps A383 and A553.

Conclusions

Although SP is not generally used to treat P. vivax infections, mutations in dhfr and dhps that confer antifolate resistance in P. vivax are common. The data strongly suggest that, when used primarily to treat falciparum malaria, SP can exert a substantial selective pressure on P. vivax populations, and this can lead to point mutations in dhfr and dhps. Accurate data on the global geographic distribution of dhfr and dhps genotypes should help to inform anti-malarial drug-use policies.

Fractions of an antimalarial neem-leaf extract have activities superior to chloroquine, and are gametocytocidal

The antimalarial activities of two fractions (IRDN-A and IRDN-B) of an extract from the leaves of the neem tree (Azadirachta indica) were compared with those of chloroquine, in in-vitro assays against Plasmodium falciparum. The asexual stages of a chloroquine-sensitive clone (ITG2F6) and a chloroquine-resistant isolate (W2) and the gametocytes of the NF 54 (BD-7) isolate of P. falciparum were used as the drug targets. Activity against the asexual stages was generally evaluated as the concentrations inhibiting the parasitaemias recorded in the control cultures, after an incubation of 48-72 h, by 50% (IC50) or 100% (IC100). For the ITG2F6 strain, the IC50 and IC100 (in microg/ml) were, respectively, 10(-5) and 10(-4) for IRDN-A, 10(-3) and 10(-2) for IRDN-B, and 10(-2) and 1.0 for chloroquine. The corresponding values for the W2 strain were 10(-5) and 1.0 for IRDN-A, and 10.0 and >100 for chloroquine (even at 100 microg/ml, chloroquine only inhibited the parasitaemia by 85%). Each of the two neem-leaf fractions lysed 50% and 100% of developing gametocytes, at 10(-3) and 1.0 microg/ml, respectively; and 50% and 100% of mature gametocytes at 10(-3) and 10(2) microg/ml, respectively. If they are found safe and effective in vivo, the neem-leaf fractions may form the basis of new antimalarial drugs that not only cure chloroquine-sensitive and chloroquine-resistant malaria but also markedly reduce transmission.

The chemotherapy of rodent malaria. LXIII. Drug combinations to impede the selection of drug resistance, part 6: the potential value of chlorproguanil and dapsone in combination, and with the addition of artesunate

Resistance is readily produced in rodent malaria using the single-dose, '2%-relapse technique' (2%RT) against the individual compounds chlorproguanil (CPG), chlorcycloguanil (CCG), cycloguanil, dapsone (DDS) and artesunate (ASN). Using the '4-day test', a low level of synergism or a simple additional action between CPG and DDS was observed with multiple dosing of these two compounds in a combination. Resistance to a 1 : 3 combination of CPG-DDS was selected in each of three parasite lines: Plasmodium berghei NK65, P. yoelii ssp. NS and P. chabaudi AS. Of these lines, P. chabaudi AS was found to be the most sensitive to the 1 : 3 combination in the 2%RT (and was also previously found to be the most sensitive when the compounds were used individually). Plasmodium chabaudi AS was also the line found most sensitive to a 7 : 21 : 300 combination of CPG-DDS-ASN (CDA). In mice infected with P. chabaudi AS, compared with the use of the individual components, the CPG-DDS combination only a gave a modest level of protection (as indicated by the increase in the time required to select resistance in the 2%RT) but the triple CDA combination was totally effective over the duration of the experiment. New pharmacokinetic data to be reported elsewhere indicate, however, that the antimalarial action of CPG in mice is exerted by a mechanism that is not associated with the drug's conversion to the antifolate triazine, CCG. The question thus arises as to how, in the present model, the protective action of CDA was effected. The present results nevertheless reinforce the hypothesis that a CDA combination, appropriately proportioned for human use, should be of practical value, in protecting the individual components, when used for the treatment of multidrug-resistant P. falciparum, and possibly other Plasmodium species, in endemic areas. Clinical trials, both with a CPG-DDS combination (Lapdap) and CDA, are currently under way in tropical Africa. Further studies are now required to determine whether DDS, CPG or an as-yet unidentified metabolite of CPG interact with ASN, and whether a simple double combination of ASN with one or other of these would be as protective, against the selection of resistance, as CDA.

Effects of amodiaquine and artesunate on sulphadoxine-pyrimethamine pharmacokinetic parameters in children under five in Mali

BACKGROUND

Sulphadoxine-pyrimethamine, in combination with artesunate or amodiaquine, is recommended for the treatment of uncomplicated malaria and is being evaluated for intermittent preventive treatment. Yet, limited data is available on pharmacokinetic interactions between these drugs.

METHODS

In a randomized controlled trial, children aged 6-59 months with uncomplicated falciparum malaria, received either one dose of sulphadoxine-pyrimethamine alone (SP), one dose of SP plus three daily doses of amodiaquine (SP+AQ) or one dose of SP plus 3 daily doses of artesunate (SP+AS). Exactly 100 μl of capillary blood was collected onto filter paper before drug administration at day 0 and at days 1, 3, 7, 14, 21 and 28 after drug administration for analysis of sulphadoxine and pyrimethamine pharmacokinetic parameters.

RESULTS

Fourty, 38 and 31 patients in the SP, SP+AQ and SP+AS arms, respectively were included in this study. The concentrations on day 7 (that are associated with therapeutic efficacy) were similar between the SP, SP+AQ and SP+AS treatment arms for sulphadoxine (median [IQR] 35.25 [27.38-41.70], 34.95 [28.60-40.85] and 33.40 [24.63-44.05] μg/mL) and for pyrimethamine (56.75 [46.40-92.95], 58.75 [43.60-98.60] and 59.60 [42.45-86.63] ng/mL). There were statistically significant differences between the pyrimethamine volumes of distribution (4.65 [3.93-6.40], 4.00 [3.03-5.43] and 5.60 [4.40-7.20] L/kg; p = 0.001) and thus elimination half-life (3.26 [2.74 -3.82], 2.78 [2.24-3.65] and 4.02 [3.05-4.85] days; p < 0.001). This study confirmed the lower SP concentrations previously reported for young children when compared with adult malaria patients.

CONCLUSION

Despite slight differences in pyrimethamine volumes of distribution and elimination half-life, these data show similar exposure to SP over the critical initial seven days of treatment and support the current use of SP in combination with either AQ or AS for uncomplicated falciparum malaria treatment in young Malian children.

Molecular markers of anti-malarial drug resistance in Lahj Governorate, Yemen: baseline data and implications

Background

This is an investigation of anti-malarial molecular markers coupled with a therapeutic efficacy test of chloroquine (CQ) against falciparum malaria in an area of unstable malaria in Lahj Governorate, Yemen. The study was aimed at assessment of therapeutic response to CQ and elucidation of baseline information on molecular markers for Plasmodium falciparum resistance against CQ and sulphadoxine/pyrimethamine (SP).

Methods

Between 2002 and 2003 the field test was conducted according to the standard WHO protocol to evaluate the therapeutic efficacy of CQ in 124 patients with falciparum malaria in an endemic area in Lahj Governorate in Yemen. Blood samples collected during this study were analysed for P. falciparum chloroquine resistance transporter gene (pfcrt)-76 polymorphisms, mutation pfcrt-S163R and the antifolate resistance-associated mutations dihydrofolate reductase (dhfr)-C59R and dihydropteroate synthase (dhps)-K540E. Direct DNA sequencing of the pfcrt gene from three representative field samples was carried out after DNA amplification of the 13 exons of the pfcrt gene.

Results

Treatment failure was detected in 61% of the 122 cases that completed the 14-day follow-up. The prevalence of mutant pfcrt T76 was 98% in 112 amplified pre-treatment samples. The presence of pfcrt T76 was poorly predictive of in vivo CQ resistance (PPV = 61.8%, 95% CI = 52.7-70.9). The prevalence of dhfr Arg-59 mutation in 99 amplified samples was 5%, while the dhps Glu-540 was not detected in any of 119 amplified samples. Sequencing the pfcrt gene confirmed that Yemeni CQ resistant P. falciparum carry the old world (Asian and African) CQ resistant haplotype CVIETSESI at positions 72,73,74,75,76,220,271, 326 and 371.

Conclusion

This is the first study to report baseline information on the characteristics and implications of anti-malarial drug resistance markers in Yemen. It is also the first report of the haplotype associated with CQR P. falciparum parasites from Yemen. Mutant pfcrtT76 is highly prevalent but it is a poor predictor of treatment failure in the study population. The prevalence of mutation dhfrArg59 is suggestive of emerging resistance to SP, which is currently a component of the recommended combination treatment of falciparum malaria in Yemen. More studies on these markers are recommended for surveillance of resistance in the study area.

An antimalarial neem leaf extract has both schizonticidal and gametocytocidal activities

A crude acetone/water (50/50) extract of neem leaves (IRAB) was evaluated for activity against the asexual (trophozoites/schizonts) and the sexual (gametocytes) forms of the malarial parasite, Plasmodium falciparum, in vitro. In separate 72 hour cultures of both asexual parasites and mature gametocytes treated with IRAB (0.5 microg/mL), parasite numbers were less than 50% of the numbers in control cultures, which had 8.0% and 8.5% parasitemia, respectively. In cultures containing 2.5 microg/mL, asexual parasites and mature and immature gametocytes were reduced to 0.1%, 0.2%, and 0% parasitemia, respectively. There were no parasites in the cultures containing 5.0 microg/mL. This extract, if found safe, may provide materials for development of new antimalarial drugs that may be useful both in treatment of malaria as well as the control of its transmission through gametocytes.

Implementing Intermittent Preventive Treatment for Malaria in Pregnancy: Review of Prospects, Achievements, Challenges and Agenda for Research

INTRODUCTION: Implementing Intermittent Preventive Treatment for malaria in Pregnancy (IPTp) with sulfadoxine-pyrimethamine (SP) through antenatal care (ANC) clinics is recommended for malaria endemic countries. Vast biomedical literature on malaria prevention focuses more on the epidemiological and cost-effectiveness analyses of the randomised controlled trials carried out in selected geographical settings. Such studies fail to elucidate the economic, psychosocial, managerial, organization and other contextual systemic factors influencing the operational effectiveness, compliance and coverage of the recommended interventions. OBJECTIVE: To review literature on policy advances, achievements, constraints and challenges to malaria IPTp implementation, emphasising on its operational feasibility in the context of health-care financing, provision and uptake, resource constraints and psychosocial factors in Africa. RESULTS: The importance of IPTp in preventing unnecessary anaemia, morbidity and mortality in pregnancy and improving childbirth outcomes is highly acknowledged, although the following factors appear to be the main constraints to IPTp service delivery and uptake: cost of accessing ANC; myths and other discriminatory socio-cultural values on pregnancy; target users, perceptions and attitudes towards SP, malaria, and quality of ANC; supply and cost of SP at health facilities; understaffing and demoralised staff; ambiguity and impracticability of user-fee exemption policy guidelines on essential ANC services; implementing IPTp, bednets, HIV and syphilis screening programmes in the same clinic settings; and reports on increasing parasite resistant to SP. However, the noted increase in the coverage of the delivery of IPTp doses in several countries justify that IPTp implementation is possible and better than not. CONCLUSION: IPTp for malaria is implemented in constrained conditions in Africa. This is a challenge for higher coverage of at least two doses and attainment of the Abuja targets. Yet, there are opportunities for addressing the existing challenges, and one of the useful options is the evaluation of the acceptability and viability of the existing intervention guidelines.

Antifolates can have a role in the treatment of Plasmodium vivax

Plasmodium vivax is a serious health concern in many regions and is sometimes inadvertently treated with sulfadoxine-pyrimethamine (SP). Mutations in the genes that encode dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) confer resistance to pyrimethamine and sulfadoxine, respectively. Numerous studies have examined the prevalence and diversity of mutations in P. vivax dhfr and some have assessed the relationship between dhfr genotype and clinical or in vitro response to pyrimethamine. Other studies have examined the impact of dhps genotype on response to sulfadoxine. These data indicate that, under certain circumstances, SP could be a valuable tool in the fight against P. vivax.

Folate metabolism as a source of molecular targets for antimalarials

Folate metabolism of the malaria parasites provides two targets for current antimalarials: dihydrofolate reductase and dihydropteroate synthase. Dihydrofolate reductase inhibitors have been used as antimalarials over the past few decades, often in combination with dihydropteroate synthase inhibitors. Resistance to these antifolate drugs developed through mutations in both target enzymes. However, limited mutation possibilities gave opportunities for the development of new drugs. Furthermore, other enzymes in the folate and related pathways are potential new targets that remain to be exploited. These include thymidylate synthase, an enzyme fused with dihydrofolate reductase in the same protein chain, serine hydroxymethyltransferase, methylene tetrahydrofolate dehydrogenase, methionine synthase and enzymes in the glycine cleavage pathway.

Antimalarial drug resistance in Africa: strategies for monitoring and deterrence

Despite the initiation in 1998 by the World Health Organization of a campaign to 'Roll Back Malaria', the rates of disease and death caused by Plasmodium falciparum malaria in sub-Saharan Africa are growing. Drug resistance has been implicated as one of the main factors in this disturbing trend. The efforts of international agencies, governments, public health officials, advocacy groups and researchers to devise effective strategies to deter the spread of drug resistant malaria and to ameliorate its heavy burden on the people of Africa have not succeeded. This review will not attempt to describe the regional distribution of drug resistant malaria in Africa in detail, mainly because information on resistance is limited and has been collected using different methods, making it difficult to interpret. Instead, the problems of defining and monitoring resistance and antimalarial drug treatment outcomes will be discussed in hopes of clarifying the issues and identifying ways to move forward in a more coordinated fashion. Strategies to improve measurement of resistance and treatment outcomes, collection and use of information on resistance, and potential approaches to deter and reduce the impact of resistance, will all be considered. The epidemiological setting and the goals of monitoring determine how antimalarial treatment responses should be measured. Longitudinal studies, with incidence of uncomplicated malaria episodes as the primary endpoint, provide the best information on which to base treatment policy changes, while simpler standard in vivo efficacy studies are better suited for ongoing efficacy monitoring. In the absence of an ideal antimalarial combination regimen, different treatment alternatives are appropriate in different settings. But where chloroquine has failed, policy changes are long overdue and action must be taken now.

Research influence on antimalarial drug policy change in Tanzania: case study of replacing chloroquine with sulfadoxine-pyrimethamine as the first-line drug

INTRODUCTION

Research is an essential tool in facing the challenges of scaling up interventions and improving access to services. As in many other countries, the translation of research evidence into drug policy action in Tanzania is often constrained by poor communication between researchers and policy decision-makers, individual perceptions or attitudes towards the drug and hesitation by some policy decision-makers to approve change when they anticipate possible undesirable repercussions should the policy change as proposed. Internationally, literature on the role of researchers on national antimalarial drug policy change is limited.

OBJECTIVES

To describe the (a) role of researchers in producing evidence that influenced the Tanzanian government replace chloroquine (CQ) with sulfadoxine-pyrimethamine (SP) as the first-line drug and the challenges faced in convincing policy-makers, general practitioners, pharmaceutical industry and the general public on the need for change (b) challenges ahead before a new drug combination treatment policy is introduced in Tanzania.

METHODS

In-depth interviews were held with national-level policy-makers, malaria control programme managers, pharmaceutical officers, general medical practitioners, medical research library and publications officers, university academicians, heads of medical research institutions and district and regional medical officers. Additional data were obtained through a review of malaria drug policy documents and participant observations were also done.

RESULTS

In year 2001, the Tanzanian Government officially changed its malaria treatment policy guidelines whereby CQ--the first-line drug for a long time was replaced with SP. This policy decision was supported by research evidence indicating parasite resistance to CQ and clinical CQ treatment failure rates to have reached intolerable levels as compared to SP and amodiaquine (AQ). Research also indicated that since SP was also facing rising resistance trend, the need for a more effective drug was indispensable but for an interim 5-10 year period it was justifiable to recommend SP that was relatively more cost-effective than CQ and AQ. The government launched the policy change considering that studies (ethically approved by the Ministry of Health) on therapeutic efficacy and cost-effectiveness of artemisinin drug combination therapies were underway. Nevertheless, the process of communicating research results and recommendations to policy-making authorities involved critical debates between policy makers and researchers, among the researchers themselves and between the researchers and general practitioners, the speculative media reports on SP side-effects and reservations by the general public concerning the rationale for policy change, when to change, and to which drug of choice.

CONCLUSION

Changing national drug policy will remain a sensitive issue that cannot be done overnight. However, to ensure that research findings are recognised and the recommendations emanating from such findings are effectively utilized, a systematic involvement of all the key stakeholders (including policy-makers, drug manufacturers, media, practitioners and the general public) at all stages of research is crucial. It also matters how and when research information is communicated to the stakeholders. Professional organizations such as the East African Network on Malaria Treatment have potential to bring together malaria researchers, policy-makers and other stakeholders in the research-to-drug policy change interface.

Intermittent preventive treatment of malaria during pregnancy: a qualitative study of knowledge, attitudes and practices of district health managers, antenatal care staff and pregnant women in Korogwe District, North-Eastern Tanzania

BACKGROUND

Intermittent preventive treatment of malaria during pregnancy (IPTp) is a key intervention in the national strategy for malaria control in Tanzania. SP, the current drug of choice, is recommended to be administered in the second and third trimesters of pregnancy during antenatal care (ANC) visits. To allow for a proper design of planned scaling up of IPT services in Tanzania it is useful to understand the IPTp strategy's acceptability to health managers, ANC service providers and pregnant women. This study assesses the knowledge, attitudes and practices of these groups in relation to malaria control with emphasis on IPTp services.

METHODS

The study was conducted in February 2004, in Korogwe District, Tanzania. It involved in-depth interviews with the district medical officer (DMO), district hospital medical officer in charge and relevant health service staff at two peripheral dispensaries, and separate focus group discussions (FGDs) with district Council Health Management Team members at district level and pregnant women at dispensary and community levels.

RESULTS

Knowledge of malaria risks during pregnancy was high among pregnant women although some women did not associate coma and convulsions with malaria. Contacting traditional healers and self-medication with local herbs for malaria management was reported to be common. Pregnant women and ANC staff were generally aware of SP as the drug recommended for IPTp, albeit some nurses and the majority of pregnant women expressed concern about the use of SP during pregnancy. Some pregnant women testified that sometimes ANC staff allow the women to swallow SP tablets at home which gives a room for some women to throw away SP tablets after leaving the clinic. The DMO was sceptical about health workers' compliance with the direct observed therapy in administering SP for IPTp due to a shortage of clean water and cups at ANC clinics. Intensified sensitization of pregnant women about the benefits of IPTp was suggested by the study participants as an important approach for improving IPTp compliance.

CONCLUSION

The successful implementation of the IPTp strategy in Tanzania depends on the proper planning of, and support to, the training of health staff and sustained sensitization of pregnant women at health facility and community levels about the benefits of IPTp for the women and their unborn babies.

Amodiaquine alone, amodiaquine+sulfadoxine-pyrimethamine, amodiaquine+artesunate, and artemether-lumefantrine for outpatient treatment of malaria in Tanzanian children: a four-arm randomised effectiveness trial

BACKGROUND

Many countries in Africa are considering a change to combination treatment for falciparum malaria because of the increase in drug resistance. However, there are few effectiveness data for these combinations. Our aim was to study the effectiveness of three drug combinations that have proven efficacious in east Africa compared with amodiaquine monotherapy.

METHODS

We undertook a randomised trial of antimalarial drug combinations for children (aged 4-59 months) with uncomplicated malaria in Muheza, Tanzania, an area with a high prevalence of resistance to sulfadoxine-pyrimethamine and chloroquine. Children were randomly allocated 3 days of amodiaquine (n=270), amodiaquine +sulfadoxine-pyrimethamine (n=507), or amodiaquine+artesunate (n=515), or a 3-day six-dose regimen of artemether-lumefantrine (n=519). Drugs were taken orally, at home, unobserved by medical staff. The primary endpoint was parasitological failure by day 14 assessed blind to treatment allocation. Secondary endpoints included day 28 follow-up and gametocyte carriage. Analysis was by intention to treat.

FINDINGS

Of 3158 children screened, 1811 were randomly assigned treatment and 1717 (95%) reached the 14-day follow-up. The amodiaquine group was stopped early by the data and safety monitoring board. By day 14, the parasitological failure rates were 103 of 248 (42%) for amodiaquine, 97 of 476 (20%) for amodiaquine+sulfadoxine-pyrimethamine, 54 of 491 (11%) for amodiaquine+artesunate, and seven of 502 (1%) for artemether-lumefantrine. By day 28, the parasitological failure rates were 182 of 239 (76%), 282 of 476 (61%), 193 of 472 (40%), and 103 of 485 (21%), respectively. The difference between individual treatment groups and the next best treatment combination was significant (p<0.001) in every case. Recrudescence rates by day 28, after correction by genotyping, were 48.4%, 34.5%, 11.2%, and 2.8%, respectively.

INTERPRETATION

The study shows how few the options are for treating malaria where there is already a high level of resistance to sulfadoxine-pyrimethamine and amodiaquine. The WHO-packaged six-dose regimen of artemether-lumefantrine is effective taken unsupervised, although cost is a major limitation.

Artesunate–dapsone–proguanil treatment of falciparum malaria: genotypic determinants of therapeutic response

The combination of chlorproguanil and dapsone is being considered as an alternative antimalarial to sulfadoxine-pyrimethamine in Africa, because of its greater efficacy against resistant parasites, and its shorter half-lives, which exert less selective pressure for the emergence of resistance. A triple artesunate-chlorproguanil-dapsone combination is under development. In a previous study of relatively low-dose chlorproguanil-dapsone in multidrug-resistant falciparum malaria in Thailand failure rates were high. Proguanil is inexpensive, widely available and very similar to chlorproguanil. The safety and efficacy of artesunate-dapsone-proguanil (artesunate 4 mg/kg, dapsone 2.5mg/kg, proguanil 8 mg/kg daily for three days), was studied prospectively in 48 Thai adult patients with acute falciparum malaria followed daily for 28 days. Eleven of these had a recrudescence of their infection. Genotyping of Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) indicated that the Pfdhfr I164L mutation was the main determinant of therapeutic outcome; all 11 failures carried this mutation (failure rate 11/37; 30%) whereas none of the 11 infections with 'wild type' 164 genotypes failed. The addition of artesunate considerably augments the antimalarial activity of the biguanide-dapsone combination, but this is insufficient for infections with parasites carrying the highly antifol-resistant Pfdhfr I164L mutation.

How do patients use antimalarial drugs? A review of the evidence

Patient adherence is a major determinant of the therapeutic response to antimalarial drugs, as most treatments are taken at home without medical supervision. With the introduction of new, effective, but more expensive antimalarials, there is concern that the high levels of efficacy observed in clinical trials may not be translated into effectiveness in the normal context of use. We reviewed available published evidence on adherence to antimalarial drugs and community drug usage; 24 studies were identified of which nine were 'intervention' studies, seven were classified as 'outcome studies', and the remainder were purely descriptive studies of antimalarial adherence. Definitions, methods, and results varied widely. Adherence was generally better when treatments were effective, and was improved by interventions focusing on provider knowledge and behaviour, packaging, and provision of correct dosages. There is insufficient information on this important subject, and current data certainly do not justify extrapolation from results with ineffective drugs to new effective treatments. Research in this area would benefit from of standardization of methodologies and the application of pharmacokinetic modelling.

Falciparum malaria: current therapeutic challenges

PURPOSE OF REVIEW

Malaria remains a major cause of death in much of the world. The routine treatment of malaria is currently threatened by rising rates of drug resistance. Moreover, mortality among children with severe and complicated malaria remains unacceptably high. Here we review trends in antimalarial drug resistance and report on the progress of newer drugs and drug combinations. We then review some recent literature regarding the pathological processes involved in the aetiology of severe malaria that may lead to improvements in the management of children with severe disease.

RECENT FINDINGS

Resistance to first line therapies, including chloroquine and sulphadoxine/pyramethamine, continues to rise in many parts of the world. The availability of newer and more effective drugs and fixed drug combinations is hampered by financial and political considerations. Nevertheless, a number of promising drugs and supportive treatments for both mild and severe malaria are at various stages of development.

SUMMARY

A range of newer drugs and fixed drug combinations are now available that are safe and effective. However, these drugs remain expensive and their introduction will require political and financial support at every level. Considerable work is still required to achieve a better understanding of the processes involved in the pathogenesis of severe and complicated malaria. Only then will it be possible to develop new and appropriate therapies that will be widely applicable.

Monitoring antimalarial drug resistance: making the most of the tools at hand

Most countries in resource-poor, malaria-endemic areas lack current and comprehensive information on antimalarial drug efficacy, resulting in sub-optimal antimalarial treatment policies. Many African countries continue to use chloroquine despite very high rates of resistance, and others have changed policies based on limited data, with mixed success. Methods for measuring antimalarial drug efficacy and resistance include in vivo studies of clinical efficacy and parasitological resistance, in vitro susceptibility assays and molecular markers for resistance to some drugs. These methods have the potential to be used in an integrated fashion to provide timely information that is useful to policy makers, and the combined use of in vivo and molecular surveys could greatly extend the coverage of resistance monitoring. Malawi, the first African country to change from chloroquine to sulfadoxine/pyrimethamine at the national level, serves as a case study for resistance monitoring and evidence-based antimalarial policies. Molecular, in vitro and in vivo studies demonstrate that chloroquine-sensitive parasites reemerged and now predominate in Malawi after it switched from chloroquine to sulfadoxine/pyrimethamine. This raises the intriguing possibility of rotating antimalarial drugs.

Safety, efficacy and determinants of effectiveness of antimalarial drugs during pregnancy: implications for prevention programmes in Plasmodium falciparum-endemic sub-Saharan Africa

Plasmodium falciparum malaria in pregnancy poses substantial risk to a pregnant woman and her neonate through anaemia and low birth weight (LBW), respectively, and is responsible for up to 35% of preventable LBW in malaria-endemic areas. Chemoprophylaxis or intermittent preventive treatment (IPT) with an effective antimalarial can ameliorate the adverse effects of malaria during pregnancy. Current guidelines from the WHO recommend that women in highly malarious areas receive IPT with an effective antimalarial. Two central considerations in evaluating drugs for use during pregnancy are safety for the mother and her foetus and effectiveness, which is determined by efficacy, cost, availability, deliverability and acceptability of the drug. These factors may be scored and potential drugs or drug combinations ranked in order of potential effectiveness for use in prevention programmes. The seven most promising regimens are all IPT, primarily because they are more easily delivered and less expensive than chemoprophylaxis. Currently, IPT with sulphadoxine-pyrimethamine (SP) is more likely to have the best overall effectiveness in preventing adverse outcomes associated with malaria in pregnancy. Its low cost, wide availability, easy deliverability and acceptability make it the clear choice in countries where efficacy of the drug remains good. For countries where resistance to SP is rising or already high, amodiaquine (alone or in combination with SP or artesunate) artesunate + SP, chlorproguanil-dapsone (with and without artesunate) and artemether-lumefantrine require urgent evaluation for use in pregnancy.

Pyrimethamine and WR99210 exert opposing selection on dihydrofolate reductase from Plasmodium vivax

Plasmodium vivax is a major public health problem in Asia and South and Central America where it is most prevalent. Until very recently, the parasite has been effectively treated with chloroquine, but resistance to this drug has now been reported in several areas. Affordable alternative treatments for vivax malaria are urgently needed. Pyrimethamine-sulfadoxine is an inhibitor of dihydrofolate reductase (DHFR) that has been widely used to treat chloroquine-resistant Plasmodium falciparum malaria. DHFR inhibitors have not been considered for treatment of vivax malaria, because initial trials showed poor efficacy against P. vivax. P. vivax cannot be grown in culture; the reason for its resistance to DHFR inhibitors is unknown. We show that, like P. falciparum, point mutations in the dhfr gene can cause resistance to pyrimethamine in P. vivax. WR99210 is a novel inhibitor of DHFR, effective even against the most pyrimethamine-resistant P. falciparum strains. We have found that it is also an extremely effective inhibitor of the P. vivax DHFR, and mutations that confer high-level resistance to pyrimethamine render the P. vivax enzyme exquisitely sensitive to WR99210. These data suggest that pyrimethamine and WR99210 would exert opposing selective forces on the P. vivax population. If used in combination, these two drugs could greatly slow the selection of parasites resistant to both drugs. If that is the case, this novel class of DHFR inhibitors could provide effective and affordable treatment for chloroquine- and pyrimethamine-resistant vivax and falciparum malaria for many years to come.