Atovaquone and proguanil for the treatment of malaria in Brazil

Are national treatment guidelines for falciparum malaria in line with WHO recommendations and is antimalarial resistance taken into consideration? - A review of guidelines in non-endemic countries

Objective

Plasmodium falciparum infections are a relatively rare but potentially deadly disease found in returning travellers. We compare the national treatment guidelines of non‐endemic countries with the WHO guidelines for the treatment of Plasmodium falciparum infections.

Methods

Review. We identified non‐endemic countries with an incidence rate of imported malaria of at least one per 100,000 population and at least 50 cases annually. Using PubMed and Google Search, we reviewed national guidelines published before 1 March 2021.

Results

Thirteen guidelines were identified. For uncomplicated falciparum malaria, 11 of 13 countries (85%) recommend an artemisinin‐based combination therapy as first‐line regimen in adults, of which artemether–lumefantrine was the most common. For severe malaria, all guidelines recommend the use of intravenous artesunate. Only three countries adjust treatment recommendations based on expected artemisinin resistance.

Conclusion

Treatment guidelines for uncomplicated falciparum malaria in non‐endemic countries generally adhere to WHO recommendations but often fail to mention the risk of drug resistance in returning travellers. Artemisinin‐based Combination Therapies (ACTs) should be the first choice for all uncomplicated malaria cases. Furthermore, the choice between ACTs should be based on regional resistance patterns.

Atovaquone-proguanil for treating uncomplicated Plasmodium falciparum malaria

BACKGROUND

The World Health Organization (WHO) in 2015 stated atovaquone-proguanil can be used in travellers, and is an option in malaria-endemic areas in combination with artesunate, as an alternative treatment where first-line artemisinin-based combination therapy (ACT) is not available or effective. This review is an update of a Cochrane Review undertaken in 2005.

OBJECTIVES

To assess the efficacy and safety of atovaquone-proguanil (alone and in combination with artemisinin drugs) versus other antimalarial drugs for treating uncomplicated Plasmodium falciparum malaria in adults and children.

SEARCH METHODS

The date of the last trial search was 30 January 2020. Search locations for published trials included the Cochrane Infectious Diseases Group Specialized Register, CENTRAL, MEDLINE, Embase, and LILACS. To include recently published and unpublished trials, we also searched ClinicalTrials.gov, the metaRegister of Controlled Trials and the WHO International Clinical Trials Registry Platform Search Portal.

SELECTION CRITERIA

Randomized controlled trials (RCTs) reporting efficacy and safety data for atovaquone-proguanil or atovaquone-proguanil with a partner drug compared with at least one other antimalarial drug for treating uncomplicated Plasmodium falciparum infection.

DATA COLLECTION AND ANALYSIS

For this update, two review authors re-extracted data and assessed certainty of evidence. We meta-analyzed data to calculate risk ratios (RRs) with 95% confidence intervals (CI) for treatment failures between comparisons, and for safety outcomes between and across comparisons. Outcome measures include unadjusted treatment failures and polymerase chain reaction (PCR)-adjusted treatment failures. PCR adjustment differentiates new infection from recrudescent infection.

MAIN RESULTS

Seventeen RCTs met our inclusion criteria providing 4763 adults and children from Africa, South-America, and South-East Asia. Eight trials reported PCR-adjusted data to distinguish between new and recrudescent infection during the follow-up period. In this abstract, we report only the comparisons against the three WHO-recommended antimalarials which were included within these trials. There were two comparisons with artemether-lumefantrine, one trial from 2008 in Ethiopia with 60 participants had two failures with atovaquone-proguanil compared to none with artemether-lumefantrine (PCR-adjusted treatment failures at day 28). A second trial from 2012 in Colombia with 208 participants had one failure in each arm (PCR-adjusted treatment failures at day 42). There was only one comparison with artesunate-amodiaquine from a 2014 trial conducted in Cameroon. There were six failures with atovaquone-proguanil at day 28 and two with artesunate-amodiaquine (PCR-adjusted treatment failures at day 28: 9.4% with atovaquone-proguanil compared to 2.9% with artesunate-amodiaquine; RR 3.19, 95% CI 0.67 to 15.22; 1 RCT, 132 participants; low-certainty evidence), although there was a similar number of PCR-unadjusted treatment failures (9 (14.1%) with atovaquone-proguanil and 8 (11.8%) with artesunate-amodiaquine; RR 1.20, 95% CI 0.49 to 2.91; 1 RCT, 132 participants; low-certainty evidence). There were two comparisons with artesunate-mefloquine from a 2012 trial in Colombia and a 2002 trial in Thailand where there are high levels of multi-resistant malaria. There were similar numbers of PCR-adjusted treatment failures between groups at day 42 (2.7% with atovaquone-proguanil compared to 2.4% with artesunate-mefloquine; RR 1.15, 95% CI 0.57 to 2.34; 2 RCTs, 1168 participants; high-certainty evidence). There were also similar PCR-unadjusted treatment failures between groups (5.3% with atovaquone-proguanil compared to 6.6% with artesunate-mefloquine; RR 0.8, 95% CI 0.5 to 1.3; 1 RCT, 1063 participants; low-certainty evidence). When atovaquone-proguanil was combined with artesunate, there were fewer treatment failures with and without PCR-adjustment at day 28 (PCR-adjusted treatment failures at day 28: 2.16% with atovaquone-proguanil compared to no failures with artesunate-atovaquone-proguanil; RR 5.14, 95% CI 0.61 to 43.52; 2 RCTs, 375 participants, low-certainty evidence) and day 42 (PCR-adjusted treatment failures at day 42: 3.82% with atovaquone-proguanil compared to 2.05% with artesunate-atovaquone-proguanil (RR 1.84, 95% CI 0.95 to 3.56; 2 RCTs, 1258 participants, moderate-certainty evidence). In the 2002 trial in Thailand, there were fewer treatment failures in the artesunate-atovaquone-proguanil group compared to the atovaquone-proguanil group at day 42 with PCR-adjustment. Whilst there were some small differences in which adverse events were more frequent in the atovaquone-proguanil groups compared to comparator drugs, there were no recurrent associations to suggest that atovaquone-proguanil is strongly associated with any specific adverse event.

AUTHORS' CONCLUSIONS

Atovaquone-proguanil was effective against uncomplicated P falciparum malaria, although in some instances treatment failure rates were between 5% and 10%. The addition of artesunate to atovaquone-proguanil may reduce treatment failure rates. Artesunate-atovaquone-proguanil and the development of parasite resistance may represent an area for further research.

Clinical implications of Plasmodium resistance to atovaquone/proguanil: a systematic review and meta-analysis

Background

Atovaquone/proguanil, registered as Malarone^®, is a fixed-dose combination recommended for first-line treatment of uncomplicated Plasmodium falciparum malaria in non-endemic countries and its prevention in travellers. Mutations in the cytochrome bc₁ complex are causally associated with atovaquone resistance.

Methods

This systematic review assesses the clinical efficacy of atovaquone/proguanil treatment of uncomplicated malaria and examines the extent to which codon 268 mutation in cytochrome b influences treatment failure and recrudescence based on published information.

Results

Data suggest that atovaquone/proguanil treatment efficacy is 89%–98% for P. falciparum malaria (from 27 studies including between 18 and 253 patients in each case) and 20%–26% for Plasmodium vivax malaria (from 1 study including 25 patients). The in vitro P. falciparum phenotype of atovaquone resistance is an IC₅₀ value >28 nM. Case report analyses predict that recrudescence in a patient presenting with parasites carrying cytochrome b codon 268 mutation will occur on average at day 29 (95% CI: 22, 35), 19 (95% CI: 7, 30) days longer than if the mutation is absent.

Conclusions

Evidence suggests atovaquone/proguanil treatment for P. falciparum malaria is effective. Late treatment failure is likely to be associated with a codon 268 mutation in cytochrome b, though recent evidence from animal models suggests these mutations may not spread within the population. However, early treatment failure is likely to arise through alternative mechanisms, requiring further investigation.

Challenges for malaria elimination in Brazil

Brazil currently contributes 42 % of all malaria cases reported in the Latin America and the Caribbean, a region where major progress towards malaria elimination has been achieved in recent years. In 2014, malaria burden in Brazil (143,910 microscopically confirmed cases and 41 malaria-related deaths) has reached its lowest levels in 35 years, Plasmodium falciparum is highly focal, and the geographic boundary of transmission has considerably shrunk. Transmission in Brazil remains entrenched in the Amazon Basin, which accounts for 99.5 % of the country’s malaria burden. This paper reviews major lessons learned from past and current malaria control policies in Brazil. A comprehensive discussion of the scientific and logistic challenges that may impact malaria elimination efforts in the country is presented in light of the launching of the Plan for Elimination of Malaria in Brazil in November 2015. Challenges for malaria elimination addressed include the high prevalence of symptomless and submicroscopic infections, emerging anti-malarial drug resistance in P. falciparum and Plasmodium vivax and the lack of safe anti-relapse drugs, the largely neglected burden of malaria in pregnancy, the need for better vector control strategies where Anopheles mosquitoes present a highly variable biting behaviour, human movement, the need for effective surveillance and tools to identify foci of infection in areas with low transmission, and the effects of environmental changes and climatic variability in transmission. Control actions launched in Brazil and results to come are likely to influence control programs in other countries in the Americas.

No Clinical or Molecular Evidence of Plasmodium falciparum Resistance to Artesunate-Mefloquine in Northwestern Brazil

We evaluated the clinical efficacy of artesunate-mefloquine (ASMQ) fixed-dose combination to treat uncomplicated malaria in Juruá Valley, the main Plasmodium falciparum transmission hotspot in Brazil. Between November 2010 and February 2013, we enrolled 162 patients aged 4-73 years, with fever or a history of fever, and a single-species P. falciparum infection confirmed by microscopy and polymerase chain reaction (PCR). All 154 patients who completed the 42-day follow-up presented an adequate clinical and parasitologic response. ASMQ was well tolerated and no adverse event caused treatment interruption. Gametocytes were detected in 46.3% patients; 35.2% had gametocytes at enrollment, whereas others developed patent gametocytemia 1-14 days after starting ASMQ. By day 3 of treatment, all subjects had cleared asexual parasitemia, but parasite DNA remained PCR detectable in 37.6% of them. Day-3 PCR positivity was associated with prolonged gametocyte carriage. We found no molecular evidence of resistance to either MQ (pfmdr1 gene amplification) or AS (mutations in selected kelch13 gene domains known to be associated with AS resistance) in the local P. falciparum population. These results strongly support the use of ASMQ as a first-line regimen to treat uncomplicated P. falciparum malaria in northwestern Brazil, but underscore the need for gametocytocidal drugs to reduce the transmission potential of ASMQ-treated patients (ClinicalTrials.gov number NCT01144702).

Atovaquone-proguanil in the treatment of imported uncomplicated Plasmodium falciparum malaria: a prospective observational study of 553 cases

Background

Each year, thousands of cases of uncomplicated malaria are imported into Europe by travellers. Atovaquone-proguanil (AP) has been one of the first-line regimens used in France for uncomplicated malaria for almost ten years. While AP’s efficacy and tolerance were evaluated in several trials, its use in “real life” conditions has never been described. This study aimed to describe outcome and tolerance after AP treatment in a large cohort of travellers returning from endemic areas.

Methods

Between September 2002 and January 2007, uncomplicated malaria treated in nine French travel clinics with AP were followed for 30 days after AP initiation. Clinical and biological data were collected at admission and during the follow-up.

Results

A total of 553 patients were included. Eighty-eight percent of them were born in Africa, and 61.8% were infected in West Africa, whereas 0.5% were infected in Asia. Migrants visiting friends and relatives (VFR) constituted 77.9% of the patients, the remainder (32.1%) were backpackers. Three-hundred and sixty-four patients (66%) fulfilled follow-up at day 7 and 265 (48%) completed the study at day 30. Three patients had treatment failure. One-hundred and seventy-seven adverse drug reactions (ADR) were reported during the follow-up; 115 (77%) of them were digestive ADR. Backpackers were more likely to experiment digestive ADR compared to VFR (OR = 3.8; CI 95% [1.8-8.2]). Twenty patients had to be switched to another regimen due to ADR.

Conclusion

This study seems to be the largest in terms of number of imported uncomplicated malaria cases treated by AP. The high rate of reported digestive ADR is striking and should be taken into account in the follow-up of patients since it could affect their adherence to the treatment. Beside AP, artemisinin combination therapy (ACT) is now recommended as first-line regimen. A comparison of AP and ACT, in terms of efficacy and tolerance, would be useful.

A pilot randomised trial of induced blood-stage Plasmodium falciparum infections in healthy volunteers for testing efficacy of new antimalarial drugs

Background

Critical to the development of new drugs for treatment of malaria is the capacity to safely evaluate their activity in human subjects. The approach that has been most commonly used is testing in subjects with natural malaria infection, a methodology that may expose symptomatic subjects to the risk of ineffective treatment. Here we describe the development and pilot testing of a system to undertake experimental infection using blood stage Plasmodium falciparum parasites (BSP). The objectives of the study were to assess the feasibility and safety of induced BSP infection as a method for assessment of efficacy of new drug candidates for the treatment of P. falciparum infection.

Methods and Findings

A prospective, unblinded, Phase IIa trial was undertaken in 19 healthy, malaria-naïve, male adult volunteers who were infected with BSP and followed with careful clinical and laboratory observation, including a sensitive, quantitative malaria PCR assay. Volunteers were randomly allocated to treatment with either of two licensed antimalarial drug combinations, artemether–lumefantrine (A/L) or atovaquone-proguanil (A/P). In the first cohort (n = 6) where volunteers received ∼360 BSP, none reached the target parasitemia of 1,000 before the day designated for antimalarial treatment (day 6). In the second and third cohorts, 13 volunteers received 1,800 BSP, with all reaching the target parasitemia before receiving treatment (A/L, n = 6; A/P, n = 7) The study demonstrated safety in the 19 volunteers tested, and a significant difference in the clearance kinetics of parasitemia between the drugs in the 13 evaluable subjects, with mean parasite reduction ratios of 759 for A/L and 17 for A/P (95% CI 120–4786 and 7–40 respectively; p<0.01).

Conclusions

This system offers a flexible and safe approach to testing the in vivo activity of novel antimalarials.

Trial Registration:

ClinicalTrials.gov NCT01055002

Atovaquone/proguanil for the prophylaxis and treatment of malaria

Increases in international travel and escalating drug resistance have resulted in a growing number of travelers at risk of contracting malaria. Drug resistance and intolerance to standard agents such as chloroquine, sulfadoxine/pyrimethamine and mefloquine has highlighted the need for new antimalarials. The recently licensed fixed combination of atovaquone and proguanil hydrochloride (Malarone) is a promising new agent to prevent and treat Plasmodium falciparum malaria. Randomized controlled trials have shown that atovaquone/proguanil is well tolerated and efficacious for the prevention and treatment of drug-resistant P. falciparum malaria. Atovaquone/proguanil is active against the liver stage of P. falciparum malaria parasites and when used as a prophylactic agent it can be discontinued shortly after leaving malaria-endemic areas, offering a clear advantage for drug adherence.

Role of US military research programs in the development of US Food and Drug Administration--approved antimalarial drugs

US military physicians and researchers helped identify the optimum treatment dose of the naturally occurring compound quinine and collaborated with the pharmaceutical industry in the development and eventual US Food and Drug Administration approval of the synthetic antimalarial drugs chloroquine, primaquine, chloroquine-primaquine, sulfadoxine-pyrimethamine, mefloquine, doxycycline, halofantrine, and atovaquone-proguanil. Because malaria parasites develop drug resistance, the US military must continue to support the creation and testing of new drugs to prevent and treat malaria until an effective malaria vaccine is developed. New antimalarial drugs also benefit civilians residing in and traveling to malarious areas.

Problem pathogens: prevention of malaria in travellers

Human infection with Plasmodium spp leading to clinical episodes of malaria probably began very early in the history of humankind and has persistently inflicted disease among human populations. Malaria is currently considered the world's most important parasitic infection. The global impact of malaria is incalculable and appears to be worsening over the past decades. Although most of this burden of disease is carried by developing tropical countries, cases of imported malaria acquired by international travel are increasingly reported. These numbers are growing because of increased travel to malaria-endemic areas and also due to increased risk of transmission in these areas. Indeed, travel has contributed to the global spread of malaria during the history of humankind. Travellers visiting malaria risk areas should use both personal protective measures and chemoprophylaxis. Non-adherence to chemoprophylactic regimens is frequently secondary to drug side-effects. Therefore, a careful risk-benefit analysis on the use of antimalarial prophylaxis should be carried out in every individual travelling to malaria risk areas. Standby malaria self-treatment represents an alternative in some travellers. However, carefully selected and geographically specific antimalarial drug regimens should be recommended to non-immune people travelling to high-risk areas.

Multiple synergistic interactions between atovaquone and antifolates against Plasmodium falciparum in vitro: a rational basis for combination therapy

The use of synergistic drug combinations for the treatment of drug-resistant malaria is a major strategy to slow the selection and spread of Plasmodium falciparum resistant strains. In order to investigate synergistic compounds, with different modes of action, as alternative candidates for combination therapy, we used standard in vitro P. falciparum cultures and an established synergy testing method to define interactions among dapsone (DDS), atovaquone (ATQ), chlorproguanil (CPG) and its triazine metabolite chlorcycloguanil (CCG). Strong synergy was observed in the combinations DDS/CCG and ATQ/CPG. Multiple combination of these drugs, DDS/CCG/CPG/ATQ also exhibited high synergy although not higher than that of either of the two drug combinations separately. The use of this triple combination DDS/CPG/ATQ, even without an increase in synergy over their double combinations, ATQ/CPG and DDS/CCG, would contribute towards slowing the selection pressure since these drugs act against different targets and would delay the selection of parasites resistant to the three drugs, extending the useful therapeutic life of these valuable compounds.

Efficacy and safety of atovaquone-proguanil compared with mefloquine in the treatment of nonimmune patients with uncomplicated P. falciparum malaria in Japan

Malaria treatment is becoming increasingly difficult due to the widespread drug resistance of Plasmodium falciparum. In Japan, only three antimalarials are approved for treatment: oral quinine, sulfadoxine-pyrimethamine, and mefloquine. Recently, however, the Research Group on Chemotherapy of Tropical Diseases introduced atovaquone-proguanil for treating drug-resistant P. falciparum malaria. This research group had also introduced mefloquine before it was licensed nationally. Using data obtained from the research group, we analyzed the efficacy and safety of atovaquone-proguanil, as compared with mefloquine, in nonimmune patients with uncomplicated P. falciparum malaria. Cures were attained in all (100%) of 20 atovaquone-proguanil-treated and 49 (98%) of 50 mefloquine-treated adults. The mean fever clearance time (FCT) and parasite clearance time (PCT) appeared to be longer in the atovaquone-proguanil group than in the mefloquine group, but the differences were not statistically significant. Three (15%) of the 20 atovaquone-proguanil-treated adults had adverse events (AEs), all of which were transient elevations of liver enzymes, while 19 (38%) of the 50 mefloquine-treated adults had AEs, including dizziness in 8 (16%) and nausea/vomiting in 7 (14%). All 3 children treated with atovaquone-proguanil were cured without developing AEs. Despite the limitations of this study in not being a formal clinical trial, atovaquone-proguanil seemed to be at least equal to, or even better than, mefloquine for the treatment of uncomplicated P. falciparum malaria in nonimmune patients, including children. Its marketing in Japan could be beneficial in offering an alternative therapeutic option. However, vigilance should be maintained on the possible occurrence of rare but severe AEs, and also of the possible spread of drug resistance.

Atovaquone-proguanil for treating uncomplicated malaria

BACKGROUND

Many conventional treatments for uncomplicated malaria are failing because malaria parasites develop resistance to them. One way to combat this resistance is to treat people with a combination of drugs, such as atovaquone-proguanil.

OBJECTIVES

To compare atovaquone-proguanil with other antimalarial drugs (alone or in combination) for treating children and adults with uncomplicated Plasmodium falciparum malaria.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group Specialized Register (June 2005), CENTRAL (The Cochrane Library Issue 2, 2005), MEDLINE (1966 to June 2005), EMBASE (1980 to June 2005), LILACS (1982 to June 2005), reference lists, and conference abstracts. We also contacted relevant pharmaceutical manufacturers and researchers.

SELECTION CRITERIA

Randomized controlled trials comparing atovaquone-proguanil with other antimalarial drugs for treating children and adults confirmed to have uncomplicated P. falciparum malaria.

DATA COLLECTION AND ANALYSIS

Three authors independently assessed trial eligibility and methodological quality, and extracted data for an intention-to-treat analysis (where possible). We used relative risk (RR) and 95% confidence intervals (CI) for dichotomous data. We contacted trial authors for additional information where needed.

MAIN RESULTS

Ten trials, with a total of 2345 participants, met the inclusion criteria. The trials were conducted in four geographical regions and were often small, but they included comparisons across eight drugs. Nine trials were funded by a pharmaceutical company, only three carried out an intention-to-treat analysis, and allocation concealment was unclear in seven. Atovaquone-proguanil had fewer treatment failures by day 28 than chloroquine (RR 0.04, 95% CI 0.00 to 0.57; 27 participants, 1 trial), amodiaquine (RR 0.22, 95% CI 0.13 to 0.36; 342 participants, 2 trials), and mefloquine (RR 0.04, 95% CI 0.00 to 0.73; 158 participants, 1 trial). There were insufficient data to draw a conclusion for this outcome from comparisons with sulfadoxine-pyrimethamine (172 participants, 2 trials), halofantrine (205 participants, 1 trial), artesunate plus mefloquine (1063 participants, 1 trial), quinine plus tetracycline (154 participants, 1 trial), and dihydroartemisinin-piperaquine-trimethoprim-primaquine (161 participants, 1 trial). Adverse events were mainly common symptoms of malaria and did not differ in frequency between groups.

AUTHORS' CONCLUSIONS

Data are limited but appear to suggest that atovaquone-proguanil is more effective than chloroquine, amodiaquine, and mefloquine. There are insufficient data for comparisons against sulfadoxine-pyrimethamine, halofantrine, artesunate plus mefloquine, quinine plus tetracycline, and dihydroartemisinin-piperaquine-trimethoprim-primaquine in treating malaria. There are not enough data to assess safety, but a number of adverse events were identified with all drugs. Large trials comparing atovaquone-proguanil with other new combination therapies are needed.

The pharmacokinetics and pharmacodynamics of atovaquone and proguanil for the treatment of uncomplicated falciparum malaria in third-trimester pregnant women

OBJECTIVE

To investigate the pharmacokinetics, safety and efficacy of the recommended 3-day treatment regimen of Malarone in third-trimester pregnant women with acute uncomplicated falciparum malaria.

METHODS

Twenty-six pregnant women in their third trimester (gestational age: 24-34 weeks) with acute uncomplicated Plasmodium falciparum malaria who fulfilled the enrollment criteria were recruited from the antenatal clinics of Mae Sot Hospital, Tak Province, Thailand, (n = 8) and the Tropical Diseases Research Centre, Ndola, Zambia (n = 18). Patients were treated with four Malarone tablets (GlaxoSmithKline: each tablet contains 250 mg atovaquone and 100 mg proguanil) once daily for 3 consecutive days. Blood samples were taken for pharmacokinetic investigations of atovaquone, proguanil, and cycloguanil up to 288 h (day 14) after the last dose. Urine samples were collected for the evaluation of proguanil and cycloguanil 0-8, 8-16, 16-24 and 24-48 h after the last dose. Efficacy assessments included the clinical and parasitological evaluation of mothers and newborns. Adverse events were evaluated at each visit to the antenatal clinics.

RESULTS

Malarone appeared to be effective and well tolerated when used for the treatment of falciparum malaria in pregnant women. All patients showed prompt clinical improvement and the disappearance of parasitaemia after treatment. There were no serious adverse effects or unexpected adverse effects and no stillbirths or spontaneous abortions. The plasma concentration-time profiles of atovaquone and proguanil in most cases were best characterised by the two-compartment open model with zero-order input with/without absorption lag time and first-order elimination. There were no significant differences in any of the pharmacokinetic parameters of atovaquone, proguanil or cycloguanil between patients from Thailand and Zambia. For atovaquone, a Cmax of 1.33-8.33 microg/ml was reached at 2.0-9.3 h after the last dose on day 2. V/F, CL/F and t(1/2beta) were 6.9-39.5 l/kg, 83-384 ml/h/kg, and 57.8-130.8 h, respectively. The Cmax and t(max) values for proguanil versus cycloguanil were 383-918 versus 0-129 ng/ml and 3.3-8.6 versus 3-12 h, respectively. V/F, CL/F, and t(1/2beta) values for proguanil were 10.7-34.0 l/kg, 431-1,662 ml/h/kg and 11.2-30.3 h. The CL(R-CG), t(1/2z), (CG), proguanil/cycloguanil metabolic ratios, AUC ratios for proguanil to cycloguanil (AUC(PG/CG)) were 107.2-1,001 ml/h/kg, 5-95 ml/h/kg, 7.8-20.7 h, 5-57, and 4.7-20.2, respectively.

CONCLUSION

The pharmacokinetics of atovaquone and cycloguanil appeared to be influenced by the pregnancy status, resulting in an decrease in the Cmax and AUC of approximately twofold.

Mechanisms of resistance of malaria parasites to antifolates

Antifolate antimalarial drugs interfere with folate metabolism, a pathway essential to malaria parasite survival. This class of drugs includes effective causal prophylactic and therapeutic agents, some of which act synergistically when used in combination. Unfortunately, the antifolates have proven susceptible to resistance in the malaria parasite. Resistance is caused by point mutations in dihydrofolate reductase and dihydropteroate synthase, the two key enzymes in the folate biosynthetic pathway that are targeted by the antifolates. Resistance to these drugs arises relatively rapidly in response to drug pressure and is now common worldwide. Nevertheless, antifolate drugs remain first-line agents in several sub-Saharan African countries where chloroquine resistance is widespread, at least partially because they remain the only affordable, effective alternative. New antifolate combinations that are more effective against resistant parasites are being developed and in one case, recently introduced into use. Combining these antifolates with drugs that act on different targets in the parasite should greatly enhance their effectiveness as well as deter the development of resistance. Molecular epidemiological techniques for monitoring parasite drug resistance may contribute to development of strategies for prolonging the useful therapeutic life of this important class of drugs.

Clinical trials of chemotherapy for falciparum malaria

Plasmodium falciparum remains one of the World's most prevalent and devastating pathogens. Mainly for economic reasons, the parasite's ability to develop resistance to drugs has not been matched by the rate at which new compounds are developed. Even so, there are new drugs (or new combinations of old drugs) currently under investigation, or in the process of development (at the moment): Pyronaridine, a well-tolerated, synthetic drug that may have utility for multi-resistant falciparum malaria in many parts of the world; however,problems remain over the formulation of this drug (which is a major determinant of its bioavailability) and its eventual cost. Chlorproguanil-dapsone (lap dap) is being studied as a possible low-cost'successor' to pyrimethamine-sulfadoxine; the utility of chlorproguanil-dapsone as 'salvage' therapy for clinical cases of pyrimethamine-sulfadoxine failure has yet to be tested in clinical trials. Atovaquone-proguanil (malarone) has utility against multi-resistant parasites; however, it is likely to be expensive (but is currently being provided free-of-charge in certain areas of Africa). Artemether-benflumetol (coartemether) combines the advantages of artemether (a rapid reduction in parasite load) with a second drug that reduces the risk of recrudescence; the cost of this combination is unclear. Rectal artesunate is being studied as an intervention to reduce the proportion of children with falciparum malaria who deteriorate to severe disease; the formulation is appropriate for use in rural health centres.

Atovaquone-proguanil (malarone): an effective treatment for uncomplicated Plasmodium falciparum malaria in travelers from Denmark

BACKGROUND

Previous experience with unacceptable adverse effects with mefloquine as treatment for uncomplicated Plasmodium falciparum malaria prompted an evaluation of the effectiveness and side effects of atovaquone-proguanil (Malarone) in a hospital setting.

METHODS

Atovaquone-proguanil was given as standard treatment (1,000/400 mgq.d. for 3 days) to 50 adults who had traveled in Africa and returned with uncomplicated Plasmodium falciparum malaria. Half of the treated patients were African and had lived outside Africa for varying periods of time; the other half were Danish-born persons without any previous immunity towards malaria.

RESULTS

All patients treated with Malarone were cured without complications. The mean fever clearance times differed among the groups and according to various degrees of prior exposure to malaria and ranged from 1.3 to 2.2 days. Adverse effects during treatment were mild, and were likely to be due to the malaria itself. Fourteen people who had acquired falciparum malaria in spite of taking proguanil-chloroquine prophylaxis were also cured uneventfully without recrudescence.

CONCLUSIONS

Malarone appears to be an effective, safe and acceptable oral treatment for uncomplicated malaria.

Atovaquone and proguanil versus amodiaquine for the treatment of Plasmodium falciparum malaria in African infants and young children

Malaria-related morbidity and mortality are greatest among young children in areas with high malaria transmission intensity. An open-label, randomized study was done to evaluate the efficacy and safety of the combination of atovaquone and proguanil formulated as pediatric-strength tablets (20 and 8 mg/kg of body weight, respectively, administered once daily for 3 days), compared with amodiaquine (10 mg/kg of body weight, once daily for 3 days), among children weighing > or =5 and <11 kg in Gabon. Two hundred patients aged 3-43 months were recruited. Use of atovaquone/proguanil resulted in a cure rate on day 28 of 95% (87 of 92 children), compared with 53% (41 of 78 children) for amodiaquine (difference, 42%; 95% CI, 30%-54%; P<.001). The incidence of adverse events was similar in both groups, and no serious adverse events were attributed to the use of atovaquone/proguanil. Atovaquone/proguanil was found to be highly effective and safe for the treatment of Plasmodium falciparum malaria in infants and young children weighing 5-10 kg in Africa.

Delayed onset of malaria--implications for chemoprophylaxis in travelers

BACKGROUND

Most antimalarial agents used by travelers act on the parasite's blood stage and therefore do not prevent late-onset illness, particularly that due to species that cause relapsing malaria. We examined the magnitude of this problem among Israeli and American travelers.

METHODS

We examined malaria surveillance data from Israel and the United States to determine the traveler's destination, the infecting species, the type of chemoprophylaxis used, and the incubation period.

RESULTS

In Israel, from 1994 through 1999, there were 300 cases of malaria among returning travelers in which one species of plasmodium could be identified. In 134 of these cases (44.7 percent), the illness developed more than two months after the traveler's return; nearly all of these cases were due to infection with Plasmodium vivax or P. ovale. In 108 of the 134 cases (80.6 percent), the patient had used an antimalarial regimen according to national guidelines. In the United States, from 1992 through 1998, there were 2822 cases of malaria among travelers in which the cause could be evaluated. Late illness developed in 987 (35.0 percent) of these travelers. The infection was due to P. vivax in 811 travelers, P. ovale in 66, P. falciparum in 59, and P. malariae in 51; 614 (62.2 percent) of those with late-onset illness had appropriately taken an effective antimalarial agent.

CONCLUSIONS

In more than one third of malaria-infected travelers, the illness developed more than two months after their return. Most of these late-onset illnesses are not prevented by the commonly used and effective blood schizonticides. Agents that act on the liver phase of malaria parasites are needed for more effective prevention of malaria in travelers.

Atovaquone-proguanil for prophylaxis and treatment of malaria

OBJECTIVE

To review the currently available information on atovaquone-proguanil for treatment and prophylaxis of malaria.

DATA SOURCES

A MEDLINE search was conducted from 1966 to February 2003 using key phrases Malarone, atovaquone, proguanil, and malaria. Further articles were identified from a manual search of the references of identified articles.

STUDY SELECTION AND DATA EXTRACTION

English-language studies with animal and human data evaluating preclinical pharmacology, human studies on pharmacokinetics, and clinical trials were evaluated. Relevant data were extracted from identified articles.

DATA SYNTHESIS

Atovaquone-proguanil has been evaluated for treatment of acute, uncomplicated malaria caused by Plasmodium falciparum in 8 clinical trials. In these studies, treatment with atovaquone-proguanil led to a higher (87-100% vs. 72-88%) or equally effective (94-100% vs. 90-100%) cure rate than the comparator antimalarial agents. Atovaquone-proguanil has been evaluated for prophylaxis of malaria in 6 clinical trials. In the 4 placebo-controlled trials for semi-immune residents or nonimmune migrants, the prophylaxis success rates in the atovaquone-proguanil and placebo arms ranged from 98% to 100% and 48% to 82%, respectively. The prophylaxis with success rates were similar among the 2 arms when atovaquone-proguanil was compared with other antimalarial regimens in nonimmune travelers. Atovaquone-proguanil was well tolerated in these clinical trials.

CONCLUSIONS

Atovaquone-proguanil is a safe and effective alternative to current recommended regimens for prophylaxis and treatment of malaria.

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.

Biguanide-atovaquone synergy against Plasmodium falciparum in vitro

The synergistic potential of a range of biguanides, their triazine metabolites, tetracyclines, and pyrimethamine in combination with atovaquone has been assessed. All five biguanides tested interacted synergistically with atovaquone against Plasmodium falciparum in vitro. All of the other compounds tested were either additive or antagonistic.

Recent Advances and New Challenges in Travel Medicine

Recent advances in travel medicine include the use of computer resources to obtain information on outbreaks and recommendations to travelers, the introduction of atovaquone/proguanil as chemoprophylaxis and treatment for malaria, the use of azithromycin as an alternative in the self-treatment of traveler's diarrhea, and the combination of hepatitis A and hepatitis B vaccines. At the same time, new challenges continue to appear. Shifts in the distribution of infections, such as West Nile virus and dengue fever, underscore the need for up-to-date information. Well-known infectious diseases, such as polio, meningococcal meningitis, and influenza are appearing in unexpected ways and settings. It is increasingly clear that travelers, while at risk for infections, also play a role in the global dispersal of pathogens, such as certain serogroups of Neisseria meningitidis and influenza. Increasing drug resistance affects the choice of drugs for treatment and chemoprophylaxis, and decisions about use of vaccines. Newly identified adverse events associated with yellow fever vaccine have prompted enhanced surveillance after vaccination and careful scrutiny of appropriate indications for the vaccine.

Drug treatment of tropical parasitic infections: recent achievements and developments

Drug development offers potential solutions to a number of tropical health diseases, although the expense of pharmaceutical research and lack of return on investment has limited the production of new agents. The greatest successes have been through the development of single dose therapy and mass treatment control programmes for a number of diseases. We review some of the current treatment regimens for malaria, intestinal helminth infection, onchocerciasis, filariasis and schistosomiasis, and their use in clinical practice. Geographical spread and emergence of drug resistant parasites have hindered the control of malaria, the most important global parasitic infection. Artemisinin compounds have proved effective antimalarial agents producing rapid reduction of parasite load and can be used in combination treatment regimens to combat multidrug resistance. Intestinal helminth infections are widespread, giving rise to nutritional deficiencies and impaired childhood cognitive development. Pregnant women in developing countries are at increased risk of morbidity. Treatment with a single dose benzimidazole such as albendazole or mebendazole has beneficial effects on morbidity and rates of transmission. Diethylcarbamazine has been used in the treatment of onchocerciasis and human filariasis. A complicated escalating dose regimen over several weeks is associated with systemic and allergic reactions and may require corticosteroid cover. Simplified regimens for mass population treatment with ivermectin have proved useful and been used in combination with single dose albendazole and diethylcarbamazine. The African Programme for Onchocerciasis Control in West and Central Africa has been one of the most successful mass control programmes virtually eliminating new infections by a combination of chemotherapy, education and vector control. Schistosomiasis is of increasing importance as a result of the creation of new snail habitats by agricultural and economic development. Praziquantel has become the most widely available and effective chemotherapy for schistosomiasis. There have been a number of reports of persistent schistosome egg shedding after treatment posing concerns about the emergence of drug resistance. Eflornithine has been successfully used in patients with human trypanosomiasis failing melarsoprol therapy however expense and availability have limited its potential. Mass control treatment programmes have targeted schoolchildren, adolescents and pregnant women. The integration of schistosomiasis, onchocerciasis, filariasis and helminth control programmes has been considered as a cost-effective method of delivering treatment. It is likely that future control will be based on this optimisation and integration of existing regimens, rather than the development of new agents.

Antiparasitic agents

Several important developments have occurred in recent years in the chemotherapy for and prophylaxis of parasitic infections. Although mefloquine is clearly the most effective agent for prevention of chloroquine-resistant falciparum malaria, its use has been compromised by side effects, both real and imagined. Well-designed studies have shown that side effects occur no more frequently with low-dose mefloquine than with chloroquine. Use of mefloquine in pregnant women has not been associated with birth defects, but the incidence of stillbirths may be increased. Malarone is a new agent that combines atovaquone and proguanil, and it may be as effective as mefloquine; however, it is not yet available in the United States. Several newer agents have appeared in response to the development of multidrug resistant Plasmodium falciparum, especially in Southeast Asia. Halofantrine is available for the treatment of mild to moderate malaria due to P. falciparum and for P. vivax infections. Because of severe toxic effects, use of halofantrine should be restricted to only those unusual and rare situations in which other agents cannot be used. Artemisinin (an extract of the Chinese herbal remedy qinghaosu) and two derivatives, artesunate and artemether, are active against multidrug resistant P. falciparum and are widely used in Asia in oral, parenteral, and rectal forms. The antibacterial azithromycin in combination with atovaquone or quinine has now been reported to treat babesiosis effectively in experimental animals and in a few patients. Azithromycin in combination with paromomycin has also shown promise in the treatment of cryptosporidiosis (and toxoplasmosis when combined with pyrimethamine) in patients with the acquired immunodeficiency syndrome (AIDS). Albendazole is currently the only systemic agent available for treatment of microsporidiosis, an infection primarily of patients with AIDS. In addition, albendazole and ivermectin have emerged as effective broad-spectrum antihelminthics, with albendazole becoming the drug of choice for hydatid disease (echinococcosis), neurocysticercosis, and most intestinal nematode infections (except strongyloidiasis and trichuriasis). Liposomal amphotericin B is the first drug approved by the Food and Drug Administration for the treatment of visceral leishmaniasis.

Atovaquone and proguanil hydrochloride followed by primaquine for treatment of Plasmodium vivax malaria in Thailand

Chloroquine-resistant Plasmodium vivax malaria has been reported in several geographical areas. The P. vivax life-cycle includes dormant hepatic parasites (hypnozoites) that cause relapsing malaria weeks to years after initial infection. Curative therapy must therefore target both the erythrocytic and hepatic stages of infection. Between July 1997 and June 1998, we conducted an open-label study in Thailand to evaluate the efficacy and tolerability of a sequential regimen of combination atovaquone (1000 mg) and proguanil hydrochloride (400 mg), once daily for 3 days, followed by primaquine (30 mg daily for 14 days) for treatment of vivax malaria. All 46 patients who completed the 3-day course of atovaquone-proguanil cleared their parasitaemia within 2-6 days. During a 12-week follow-up period in 35 patients, recurrent parasitaemia occurred in 2. Both recurrent episodes occurred 8 weeks after the start of therapy, consistent with relapse from persistent hypnozoites rather than recrudescence of persistent blood-stage parasites. The dosing regimen was well tolerated. Results of this trial indicate that atovaquone-proguanil followed by primaquine is safe and effective for treatment of vivax malaria.

Combination atovaquone and proguanil hydrochloride vs. halofantrine for treatment of acute Plasmodium falciparum malaria in children

BACKGROUND

Malaria is a major cause of pediatric mortality in sub-Saharan Africa. Worldwide estimates of mortality among children with Plasmodium falciparum malaria range from 1 to 2 million deaths per year. Management of malaria is increasingly difficult because of the global spread of drug-resistant strains of P. falciparum. There is an urgent need for safe and effective new therapies to treat multidrug-resistant malaria.

METHODS

This open label, randomized trial compared atovaquone and proguanil hydrochloride with halofantrine for treatment of acute, uncomplicated P. falciparum malaria in children age 3 to 12 years (84 patients per group). Study drug dosages were adjusted by weight (approximately 20 and 8 mg/kg daily for three doses for atovaquone and proguanil hydrochloride and 8 mg/kg every 6 h for three doses for halofantrine). Patients were monitored by serial clinical and laboratory assessments for 28 days after starting treatment.

RESULTS

Both regimens were effective (cure rate, 93.8% for atovaquone and proguanil hydrochloride and 90.4% for halofantrine) and produced prompt defervescence. Mean parasite clearance times were 50.2 h for halofantrine and 64.9 h for atovaquone and proguanil hydrochloride. More adverse experiences were reported in children treated with halofantrine (119) than with atovaquone and proguanil hydrochloride (73).

CONCLUSIONS

In Kenyan children the combination of atovaquone and proguanil hydrochloride has efficacy comparable with that of halofantrine for treatment of acute uncomplicated multidrug-resistant falciparum malaria and is associated with a lower rate of adverse events.

Atovaquone and proguanil versus pyrimethamine/sulfadoxine for the treatment of acute falciparum malaria in Zambia

Atovaquone and proguanil hydrochloride are blood schizonticides that demonstrate in vitro synergy against drug-resistant strains of Plasmodium falciparum. When coadministered, they may therefore be effective for the treatment of malaria in regions where there is known or suspected drug resistance. In an open-label, randomized, parallel-group, clinical trial conducted in Zambia, 163 patients (age range, 14 to 54 years) with acute P falciparum malaria were randomly assigned to receive treatment with atovaquone and proguanil hydrochloride (1000 and 400 mg, respectively, administered orally at 24-hour intervals for 3 doses; n = 82) or pyrimethamine/sulfadoxine (75/1500 mg administered orally as a single dose; n = 81). Efficacy was assessed by cure rate (the percentage of patients in whom parasitemia was eliminated and did not recur during 28 days of follow-up), parasite clearance time (PCT), and fever clearance time (FCT). Safety was determined by sequential clinical and laboratory assessments over 28 days. Cure rates did not differ significantly between patients treated with atovaquone and proguanil (100%) and those treated with pyrimethamine/sulfadoxine (98.8%). Patients in the atovaquone and proguanil group had a significantly shorter FCT than patients in the pyrimethamine/sulfadoxine group (mean, 30.4 vs 44.9 hours; P < 0.05) but a longer PCT (mean, 64.0 vs 51.4 hours; P < 0.05). Both treatments were well tolerated; adverse events and laboratory abnormalities were typical of those normally observed in patients with malaria. In this study, the combination of atovaquone and proguanil was equally effective and as well tolerated as pyrimethamine/sulfadoxine for the treatment of acute, uncomplicated, drug-resistant falciparum malaria in Zambia.

Malaria in travelers. Epidemiology, disease, and prevention

The combination of increases in international travel and escalating drug resistance has resulted in a growing number of travelers contracting malaria. Preventing malaria-associated morbidity and mortality will require improved health information for travelers about the risk of malaria and appropriate preventive measures, improved recognition of infection by physicians, rapid and accurate laboratory diagnosis, and prompt initiation of effective therapy.

Randomised placebo-controlled study of atovaquone plus proguanil for malaria prophylaxis in children

BACKGROUND

The combination of atovaquone and proguanil is highly effective and safe for the treatment of Plasmodium falciparum malaria. We aimed in this randomised, double-blind, placebo-controlled study to assess the efficacy and safety of this combination for malaria prophylaxis.

METHODS

320 children who lived in a hyperendemic area for P falciparum malaria were stratified by weight and randomly assigned atovaquone plus proguanil or placebo once daily for 12 weeks. All children received initial curative treatment with atovaquone and proguanil before the start of chemosuppression. We recorded adverse events daily and collected thick blood smears once a week. The primary endpoint was a positive blood smear.

FINDINGS

25 of 140 children in the placebo group and none of the 125 children in the atovaquone plus proguanil group had positive smears during chemosuppression (p<0.001). Adverse events during the chemosuppression phase did not differ between the groups.

INTERPRETATION

The combination of atovaquone plus proguanil is a highly effective and well-tolerated chemosuppressive antimalarial in children. This drug combination could replace current regimens.

Efficacy and pharmacokinetics of atovaquone and proguanil in children with multidrug-resistant Plasmodium falciparum malaria

A trial was conducted in 32 Thai children with uncomplicated multidrug-resistant falciparum malaria to assess the efficacy, safety and pharmacokinetics of atovaquone and proguanil; plasma concentrations of atovaquone, proguanil and its metabolite, cycloguanil, were measured in a subset of 9 children. The children received atovaquone (17 mg/kg/d for 3 d) plus proguanil (7 mg/kg/d for 3 d). Twenty-six children who had only Plasmodium falciparum infection and remained in hospital for 28 d were assessed for drug efficacy. The combination regimen produced a cure rate of 100%. Parasite and fever clearance times were 47 h (range 8-75) and 50 h (range 7-111), respectively. Atovaquone and proguanil were rapidly absorbed, with median time to peak concentrations of 6 h (range 6-24) and 6 h (range 6-12), respectively. Peak concentrations of cycloguanil were achieved between 6 and 12 h (median 6) after administration of proguanil. Mean peak plasma concentration of atovaquone on day 3 was 5.1 micrograms/mL (SD = 2.1). The day 3 mean peak plasma concentration of proguanil was 306 ng/mL (SD = 108) compared with 44.3 ng/mL (SD = 27.3) for cycloguanil. Mean values for the AUC (area under plasma concentration-time curve) were 161.8 micrograms/mL.h (SD = 126.9) for atovaquone, 4646 ng/mL.h (SD = 1226) for proguanil, and 787 ng/mL.h (SD = 397) for cycloguanil. Terminal elimination half-lives of atovaquone, proguanil and cycloguanil were estimated as 31.8 h (SD = 8.9), 14.9 h (SD = 3.3) and 14.6 h (SD = 2.6), respectively. No major adverse effect was attributable to the study drugs. Atovaquone/proguanil combination is safe and highly effective, and should be especially valuable for treatment of multidrug-resistant falciparum malaria.