Pharmacologic Advances in the Global Control and Treatment of Malaria: Combination Therapy and Resistance

Current Status of Malaria Control and Elimination in Africa: Epidemiology, Diagnosis, Treatment, Progress and Challenges

The African continent carries the greatest malaria burden in the world. Falciparum malaria especially has long been the leading cause of death in Africa. Climate, economic factors, geographical location, human intervention and unstable security are factors influencing malaria transmission. Due to repeated infections and early interventions, the proportion of clinically atypical malaria or asymptomatic plasmodium carriers has increased significantly, which easily lead to misdiagnosis and missed diagnosis. African countries have made certain progress in malaria control and elimination, including rapid diagnosis of malaria, promotion of mosquito nets and insecticides, intermittent prophylactic treatment in high-risk groups, artemisinin based combination therapies, and the development of vaccines. Between 2000 and 2022, there has been a 40% decrease in malaria incidence and a 60% reduction in mortality rate in the WHO African Region. However, many challenges are emerging in the fight against malaria in Africa, such as climate change, poverty, substandard health services and coverage, increased outdoor transmission and the emergence of new vectors, and the growing threat of resistance to antimalarial drugs and insecticides. Joint prevention and treatment, identifying molecular determinants of resistance, new drug development, expanding seasonal malaria chemo-prevention intervention population, and promoting the vaccination of RTS, S/AS01 and R21/Matrix-M may help to solve the dilemma. China's experience in eliminating malaria is conducive to Africa's malaria prevention and control, and China-Africa cooperation needs to be constantly deepened and advanced. Our review aims to help the global public develop a comprehensive understanding of malaria in Africa, thereby contributing to malaria control and elimination.

Malaria chemoprevention and drug resistance: a review of the literature and policy implications

Chemoprevention strategies reduce malaria disease and death, but the efficacy of anti-malarial drugs used for chemoprevention is perennially threatened by drug resistance. This review examines the current impact of chemoprevention on the emergence and spread of drug resistant malaria, and the impact of drug resistance on the efficacy of each of the chemoprevention strategies currently recommended by the World Health Organization, namely, intermittent preventive treatment in pregnancy (IPTp); intermittent preventive treatment in infants (IPTi); seasonal malaria chemoprevention (SMC); and mass drug administration (MDA) for the reduction of disease burden in emergency situations. While the use of drugs to prevent malaria often results in increased prevalence of genetic mutations associated with resistance, malaria chemoprevention interventions do not inevitably lead to meaningful increases in resistance, and even high rates of resistance do not necessarily impair chemoprevention efficacy. At the same time, it can reasonably be anticipated that, over time, as drugs are widely used, resistance will generally increase and efficacy will eventually be lost. Decisions about whether, where and when chemoprevention strategies should be deployed or changed will continue to need to be made on the basis of imperfect evidence, but practical considerations such as prevalence patterns of resistance markers can help guide policy recommendations.

Malaria parasite clearance from patients following artemisinin-based combination therapy in Côte d'Ivoire

Introduction

Parasite clearance is useful to detect artemisinin resistance. The aim of this study was to investigate parasite clearance in patients treated with artesunate + amodiaquine (AS + AQ) and artemether + lumefantrine (AL): the two artemisinin-based combination therapies (ACTs) recommended in the first-line treatment of uncomplicated malaria in Côte d’Ivoire.

Methods

This study was conducted in Bouaké, Côte d’Ivoire, from April to June 2016. Patients aged at least 6 months with uncomplicated malaria and treated with AS + AQ or AL were hospitalized for 3 days, and follow-up assessments were performed on days 3, 7, 14, 21, 28, 35, and 42. Blood smears were collected at the time of screening, pre-dose, and 6-hour intervals following the first dose of administration until two consecutive negative smears were recorded, thereafter at day 3 and follow-up visits. Parasite clearance was determined using the Worldwide Antimalarial Resistance Network’s parasite clearance estimator. The primary end points were parasite clearance rate and time.

Results

A total of 120 patients (57 in the AS + AQ group and 63 in the AL group) were randomized among 298 patients screened. The median parasite clearance time was 30 hours (IQR, 24–36 hours), for each ACT. The median parasite clearance rate had a slope half-life of 2.36 hours (IQR, 1.85–2.88 hours) and 2.23 hours (IQR, 1.74–2.63 hours) for AS + AQ and AL, respectively. The polymerase chain reaction-corrected adequate clinical and parasitological response was 100% and 98.07% at day 42 for AS + AQ and AL, respectively.

Conclusion

Patients treated with AS + AQ and AL had cleared parasites rapidly. ACTs are still efficacious in Bouaké, Côte d’Ivoire, but continued efficacy monitoring of ACTs is needed.

Multidrug-resistant malaria and the impact of mass drug administration

Based on the emergence and spread throughout the Greater Mekong Subregion (GMS) of multiple artemisinin-resistant lineages, the prevalence of multidrug resistance leading to high rates of artemisinin-based combination treatment failure in parts of the GMS, and the declining malaria burden in the region, the World Health Organization has recommended complete elimination of falciparum malaria from the GMS. Mass drug administration (MDA) is being piloted as one elimination intervention to be employed as part of this effort. However, concerns remain as to whether MDA might exacerbate the already prevalent problem of multidrug resistance in the region. In this review, we briefly discuss challenges of MDA, the use of MDA in the context of multidrug-resistant malaria, and the potential of different drug combinations and drug-based elimination strategies for mitigating the emergence and spread of resistance.

Nitazoxanide anthelmintic activity against the enteral and parenteral phases of trichinellosis in experimentally infected rats

Most of the drugs used for the treatment of trichinellosis show a limited bioavailability and a high degree of resistance. Therefore, this study aimed to characterize the anthelmintic potential activity of nitazoxanide (NTZ) in a rat model of experimental trichinellosis. Animals were divided into three groups; group I, infected and non-treated; group II, received NTZ for three days post-infection (dpi) and group III, received NTZ 30 dpi for 14 consecutive days. Treatment efficacy was assessed by Trichinella spiralis adult and larval counts, histopathological studies of the small intestine and muscles and inducible nitric oxide synthase (iNOS) expression in the small intestine. T. spiralis adult count was reduced in NTZ -treated group (66.6%) and the larval count decreased to 68.7 and 76.7% in the early and late treatment, respectively. The infected non-treated rats showed massive inflammatory cellular infiltration in the small intestines and muscles. This inflammatory response was minor in the treated groups and was accompanied by a decrease in iNOS expression. Moreover, in group III, the larvae were replaced by homogenized substance with some destructive changes in the capsule. In conclusion, NTZ showed a promising activity against enteral and more effect in parenteral phases of trichinellosis.

Anti-malarial prescribing practices in Sudan eight years after introduction of artemisinin-based combination therapies and implications for development of drug resistance

BACKGROUND

The World Health Organization (WHO) recommends artemisinin-based combination therapies (ACTs) as first-line treatment for uncomplicated malaria. Sudan revised its malaria treatment policy accordingly in 2004. However, eight years after ACTs were introduced in Sudan the patterns of ACT prescribing practices among health care providers remain unclear. We systematically analyzed use of ACTs in a large number of primary health facilities and we discuss the public health implications of our findings.

METHODS

This cross-sectional study was based on WHO's guidance for investigating drug use in health facilities. Data were collected from 40 randomly selected primary health centers in five localities in Gezira State, Sudan. The primary outcome of the study was the proportion of patients who were adequately managed according to Sudan's recommended malaria treatment guidelines. Twelve drug-use indicators were used to assess key ACT prescribing practices.

RESULTS

One thousand and two hundred patients diagnosed with uncomplicated malaria were recruited into the study. ACT was prescribed for 88.6%patients and artemether injections were (incorrectly) prescribed in 9.5% of cases. Only 40.9% of patients in the study were correctly diagnosed and 26.9% were adequately managed according to the nationally recommended treatment guidelines. Incorrect prescribing activities included failure to use generic medicine names (88.2%), incorrect dosage (27.7%), and unexplained antibiotic co-prescription (24.2%). Dispensing practices were also poor, with labeling practices inadequate (97.1%) and insufficient information given to patients about their prescribed treatment (50.5%).

CONCLUSION

Irrational malaria treatment practices are common in Sudan. This has important public health implications since failure to adhere to nationally recommended guidelines could play a role in the future development of drug resistance. As such, identifying ways to improve the anti-malarial prescribing practices of heath workers in Sudan may be a priority.

Population pharmacokinetics of mefloquine, administered as a fixed-dose combination of artesunate-mefloquine in Indian patients for the treatment of acute uncomplicated Plasmodium falciparum malaria

Background

Fixed-dose combinations of artemisinin combination therapy are strongly recommended to facilitate drug administration and compliance. New fixed-dose combinations must nevertheless be evaluated in relevant populations in terms of efficacy and pharmacokinetics.

Methods

A single-arm, open-label, clinical trial was performed in Indian patients with acute uncomplicated Plasmodium falciparum malaria to investigate the efficacy and the pharmacokinetics of mefloquine when combined with artesunate in a fixed-dose combination (400/200 mg of mefloquine base/artesunate). The pharmacokinetic analysis was performed using a population approach.

Results

Seventy-seven patients were included in the study. Mefloquine pharmacokinetics obeys a two-compartment model with first-order absorption and elimination. Mean parameter estimates (% inter-individual variability) were as follows: 0.16 h^-1 (75%) for the absorption rate constant, 1.13 L/h (30%) for the apparent plasma clearance, 271 L (21%) for the apparent central distribution volume, 344 L (54%) for the apparent peripheral distribution volume, and 1.43 L/h for the apparent distribution clearance. These values were consistent with the pharmacokinetic results described in Thai patients. No significant covariate was found for clearance. Body weight explained the inter-individual variability of the apparent central and peripheral distribution volumes. The PCR-adjusted efficacy of the treatment was 100%.

Conclusions

The lack of significant covariate explaining the inter-individual variability of mefloquine clearance, combined with the excellent efficacy, supports the use of the standard 200/400 mg of artesunate-mefloquine fixed-dose combination in Indian patients with uncomplicated P. falciparum malaria.

Trial Registration

Clinical Trial Registration: ISRCTN70618692

Direct observation of outpatient management of malaria in a rural Ghanaian district

INTRODUCTION

In Ghana, malaria continues to top outpatient morbidities; accounting for about 40% of all attendances. Effective case-management is key to its control. We evaluated case-management practices of uncomplicated malaria in Kwahu South District (KSD) health facilities to determine their conformity to guidelines.

METHODS

We conducted a cross sectional survey at all public health facilities in three randomly selected sub-districts in KSD. A non-participatory observation of suspected malaria consultations was conducted. Suspected malaria was defined as any person with fever (by history or measured axillary temperature > or equal 37.5 oC) presenting at the selected health facilities between 19th and 29th April 2013. Findings were expressed as frequencies, relative frequencies, mean (± standard deviation) and median.

RESULTS

Of 70 clinical observations involving 10 prescribers in six health facilities, 40 (57.1%) were females and 16 (22.9%) were below five years. Median age was 18 years (interquartile range: 5-33). Overall, 63 (90.0%) suspected case-patients had diagnostic tests. Two (3.6%) were treated presumptively. All 31 confirmed and 10 (33.3%) of the test negative case-patients received Artemisinin-based Combination Therapies (ACTs). However, only 12 (27.9%) of the 43 case-patients treated with ACT received Artesunate-Amodiaquine (AA). Only three (18.8%) of the under-fives were examined for non-malarial causes of fever. Mean number of drugs per patient was 3.7 drugs (± 1.1). Only 45 (64.3%) patients received at least one counseling message.

CONCLUSION

Conformity of malaria case-management practices to guidelines in KSD was suboptimal. Apart from high rate of diagnostic testing and ACT use, prescription of AA, physical examination and counseling needed improvement.

Emerging artemisinin resistance in the border areas of Thailand

Emergence of artemisinin resistance has been confirmed in Cambodia and the border areas of Thailand, the well-known hotspots of multidrug resistance Plasmodium falciparum. It appears to be spreading to the western border of Thailand along the Thai-Myanmar border, and will probably spread to other endemic areas of the world in the near future. This raises a serious concern on the long-term efficacy of artemisinin-based combination therapies, as these combination therapies currently constitute the last effective and most tolerable treatment for multidrug-resistant Plasmodium falciparum. Attempts have been made by a diverse array of stakeholders to prevent the emergence of new foci of artemisinin resistance, as well as to limit the spread of resistance to the original foci. The success in achieving this goal depends on effective integration of containment and surveillance programs with other malaria control measures, with support from both basic and operational research.

Antiplasmodial activity of sesquiterpene lactones and a sucrose ester from Vernonia guineensis Benth. (Asteraceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Aqueous preparations of Vernonia guineensis Benth. (Asteraceae) are used in Cameroonian folk medicine as a general stimulant and to treat various illnesses and conditions including malaria, bacterial infections and helminthic infestations.

MATERIALS AND METHODS

Ten gram samples of the leaf and tuber powders of Vernonia guineensis were extracted separately using dichloromethane, methanol and distilled water. The extracts were dried in vacuo and used in bioassays. These extracts and three compounds previously isolated from Vernonia guineensis [vernopicrin (1), vernomelitensin (2) and pentaisovalerylsucrose (3)] were screened for antiplasmodial activity against chloroquine (CQ)-sensitive (Hb3) and CQ-resistant (Dd2) Plasmodium falciparum lines.

RESULTS

Crude extracts and pure compounds from Vernonia guineensis showed antiplasmodial activity against both Hb3 and Dd2. The IC50 values of extracts ranged from 1.64 to 27.2 µg/ml for Hb3 and 1.82-30.0 µg/ml for Dd2; those for compounds 1, 2 and 3 ranged from 0.47 to 1.62 µg/ml (1364-1774 nM) for Hb3 and 0.57-1.50 µg/ml (1644-2332nM) for Dd2. None of the crude extracts or pure compounds was observed to exert toxic effects on the erythrocytes used to cultivate the Plasmodium falciparum lines.

CONCLUSION

In Cameroonian folk medicine, Vernonia guineensis may be used to treat malaria in part due to the antiplasmodial activity of sesquiterpene lactones (1, 2), a sucrose ester (3) and perhaps other compounds present in crude plant extracts. Exploring the safety and antiplasmodial efficacy of these compounds in vivo requires further study.

Access to artemisinin-based anti-malarial treatment and its related factors in rural Tanzania

BACKGROUND

Artemisinin-based combination treatment (ACT) has been widely adopted as one of the main malaria control strategies. However, its promise to save thousands of lives in sub-Saharan Africa depends on how effective the use of ACT is within the routine health system. The INESS platform evaluated effective coverage of ACT in several African countries. Timely access within 24 hours to an authorized ACT outlet is one of the determinants of effective coverage and was assessed for artemether-lumefantrine (Alu), in two district health systems in rural Tanzania.

METHODS

From October 2009 to June 2011 we conducted continuous rolling household surveys in the Kilombero-Ulanga and the Rufiji Health and Demographic Surveillance Sites (HDSS). Surveys were linked to the routine HDSS update rounds. Members of randomly pre-selected households that had experienced a fever episode in the previous two weeks were eligible for a structured interview. Data on individual treatment seeking, access to treatment, timing, source of treatment and household costs per episode were collected. Data are presented on timely access from a total of 2,112 interviews in relation to demographics, seasonality, and socio economic status.

RESULTS

In Kilombero-Ulanga, 41.8% (CI: 36.6-45.1) and in Rufiji 36.8% (33.7-40.1) of fever cases had access to an authorized ACT provider within 24 hours of fever onset. In neither of the HDSS site was age, sex, socio-economic status or seasonality of malaria found to be significantly correlated with timely access.

CONCLUSION

Timely access to authorized ACT providers is below 50% despite interventions intended to improve access such as social marketing and accreditation of private dispensing outlets. To improve prompt diagnosis and treatment, access remains a major bottle neck and new more innovative interventions are needed to raise effective coverage of malaria treatment in Tanzania.

Reduced susceptibility of Plasmodium falciparum to artesunate in southern Myanmar

Background

Plasmodium falciparum resistance to artemisinins, the first line treatment for malaria worldwide, has been reported in western Cambodia. Resistance is characterized by significantly delayed clearance of parasites following artemisinin treatment. Artemisinin resistance has not previously been reported in Myanmar, which has the highest falciparum malaria burden among Southeast Asian countries.

Methods

A non-randomized, single-arm, open-label clinical trial of artesunate monotherapy (4 mg/kg daily for seven days) was conducted in adults with acute blood-smear positive P. falciparum malaria in Kawthaung, southern Myanmar. Parasite density was measured every 12 hours until two consecutive negative smears were obtained. Participants were followed weekly at the study clinic for three additional weeks. Co-primary endpoints included parasite clearance time (the time required for complete clearance of initial parasitemia), parasite clearance half-life (the time required for parasitemia to decrease by 50% based on the linear portion of the parasite clearance slope), and detectable parasitemia 72 hours after commencement of artesunate treatment. Drug pharmacokinetics were measured to rule out delayed clearance due to suboptimal drug levels.

Results

The median (range) parasite clearance half-life and time were 4.8 (2.1–9.7) and 60 (24–96) hours, respectively. The frequency distributions of parasite clearance half-life and time were bimodal, with very slow parasite clearance characteristic of the slowest-clearing Cambodian parasites (half-life longer than 6.2 hours) in approximately 1/3 of infections. Fourteen of 52 participants (26.9%) had a measurable parasitemia 72 hours after initiating artesunate treatment. Parasite clearance was not associated with drug pharmacokinetics.

Conclusions

A subset of P. falciparum infections in southern Myanmar displayed markedly delayed clearance following artemisinin treatment, suggesting either emergence of artemisinin resistance in southern Myanmar or spread to this location from its site of origin in western Cambodia. Resistance containment efforts are underway in Myanmar.

Trial Registration

Australian New Zealand Clinical Trials Registry ACTRN12610000896077

No evidence of delayed parasite clearance after oral artesunate treatment of uncomplicated falciparum malaria in Mali

Plasmodium falciparum resistance to artemisinins by delayed parasite clearance is present in Southeast Asia. Scant data on parasite clearance after artemisinins are available from Africa, where transmission is high, burden is greatest, and artemisinin use is being scaled up. Children 1-10 years of age with uncomplicated malaria were treated with 7 days of artesunate and followed for 28 days. Blood smears were done every 8 hours until negative by light microscopy. Results were compared with a similar study conducted in the same village in 2002-2004. The polymerase chain reaction-corrected cure rate was 100%, identical to 2002-2004. By 24 hours after treatment initiation, 37.0% of participants had cleared parasitemia, compared with 31.9% in 2002-2004 (P = 0.5). The median parasite clearance time was 32 hours. Only one participant still had parasites at 48 hours and no participant presented parasitemia at 72 hours. Artesunate was highly efficacious, with no evidence of delayed parasite clearance. We provide baseline surveillance data for the emergence or dissemination of P. falciparum resistance in sub-Saharan Africa.

A longitudinal trial comparing chloroquine as monotherapy or in combination with artesunate, azithromycin or atovaquone-proguanil to treat malaria

Background

The predominance of chloroquine-susceptible falciparum malaria in Malawi more than a decade after chloroquine's withdrawal permits contemplation of re-introducing chloroquine for targeted uses. We aimed to compare the ability of different partner drugs to preserve chloroquine efficacy and prevent the re-emergence of resistance.

Methodology/Principal Findings

Children with uncomplicated malaria were enrolled at a government health center in Blantyre, Malawi. Participants were randomized to receive chloroquine alone or combined with artesunate, azithromycin or atovaquone-proguanil for all episodes of uncomplicated malaria for one year. The primary outcome was incidence of clinical malaria. Secondary endpoints included treatment efficacy, and incidence of the chloroquine resistance marker pfcrt T76 and of anemia. Of the 640 children enrolled, 628 were included in the intention-to-treat analysis. Malaria incidence (95% confidence interval) was 0.59 (.46–.74), .61 (.49–.76), .63 (.50–.79) and .68 (.54–.86) episodes/person-year for group randomized to receive chloroquine alone or in combination with artesunate, azithromycin or atovaquone-proguanil respectively and the differences were not statistically significant. Treatment efficacy for first episodes was 100% for chloroquine monotherapy and 97.9% for subsequent episodes of malaria. Similar results were seen in each of the chloroquine combination groups. The incidence of pfcrt T76 in pure form was 0%; mixed infections with both K76 and T76 were found in two out of 911 infections. Young children treated with chloroquine-azithromycin had higher hemoglobin concentrations at the study's end than did those in the chloroquine monotherapy group.

Conclusion/Significance

Sustained chloroquine efficacy with repeated treatment supports the eventual re-introduction of chloroquine combinations for targeted uses such as intermittent preventive treatment.

Trial Registration:

ClinicalTrials.gov NCT00379821

In vitro and in vivo efficacy of tribendimidine and its metabolites alone and in combination against the hookworms Heligmosomoides bakeri and Ancylostoma ceylanicum

Worldwide, 3 billion people are at risk of hookworm infection, particularly in resource-poor countries. While control of soil-transmitted helminthiases relies mostly on chemotherapy, only few drugs are available and concern about potential emergence of drug resistance is rising. In the present study, tribendimidine, a derivative of amidantel, and its metabolites deacylated amidantel (dADT) and acetylated deacylated amidantel (AdADT) were tested in vitro and in vivo against Heligmosomoides bakeri and Ancylostoma ceylanicum, two hookworm rodent models, alone or in combination with standard drugs. Tribendimidine achieved IC(50)s ≤ 5 μg/ml against both H. bakeri third-stage larvae and adults in vitro and a single 2 mg/kg oral dose resulted in complete worm elimination in vivo. Comparable results were obtained with dADT, whereas AdADT displayed no effect in vitro and gave a moderate worm burden reduction of 42.9% in H. bakeri-infected mice. Tribendimidine combined with albendazole, levamisole or ivermectin revealed antagonistic interactions against H. bakeri in vitro and no significant killing effect in vivo. Tribendimidine and dADT exerted high efficacies against A. ceylanicum third-stage larvae (IC(50)s < 0.5 μg/ml) whereas adults were moderately affected in vitro (IC(50)s > 88 μg/ml). In vivo at single oral doses of 10 mg/kg, dADT showed a slightly higher efficacy than tribendimidine, achieving worm burden reductions of 87.4% and 74.8%, respectively. At the same dose, AdADT reduced the worm burden by 57.9%. Synergistic interactions were observed with tribendimidine-levamisole combinations against A. ceylanicum in vitro (combination index at IC(50)=0.5), and in vivo (combination index at ED(90)=0.19). In conclusion, tribendimidine and dADT show potent anti-hookworm properties. The potential of the promising tribendimidine-levamisole combination should be investigated in greater detail.

Nitazoxanide: In vitro and in vivo drug effects against Trichuris muris and Ancylostoma ceylanicum, alone or in combination

Soil-transmitted helminths cause more than 1 billion human infections globally, mostly in the poorest regions of the world. Control relies essentially on a limited panel of four drugs, and drug resistance might be inescapable. Nitazoxanide, an anti-infective drug, has been shown to exert anthelmintic activity in human clinical trials. In the present work, nitazoxanide was tested alone or combined with commercialized anthelmintics on Trichuris muris, a whipworm mouse model, and Ancylostoma ceylanicum, a hookworm hamster model, in vitro and in vivo. IC50s of ⩽1 and 12.87 μg/ml were achieved with nitazoxanide on T. muris third-stage larvae (L3) and adult worms in vitro, respectively. An IC50 of ⩽1 μg/ml was obtained exposing A. ceylanicum adults worms to nitazoxanide, whereas A. ceylanicum L3 were not affected. Using scanning electron microscopy, the tegument of adult T. muris appeared unchanged following nitazoxanide treatment, whereas swellings were seen on the tegument of the anterior region of half of the A. ceylanicum specimen analyzed. Synergism was observed in vitro when nitazoxanide was combined with levamisole or ivermectin on T. muris adult worms, and when combined with levamisole, pyrantel pamoate, or ivermectin on A. ceylanicum adult worms. In T. muris-infected mice, oral nitazoxanide achieved worm burden reductions of 56.09% and 17.37% following a single dose of 100 mg/kg and three doses of 50 mg/kg, respectively. None of the tested drug combinations displayed activity on T. muris in vivo. In A. ceylanicum-infected hamsters, no effect was observed for oral nitazoxanide alone, and none of the tested combinations reached the threshold for additive effect. In conclusion, nitazoxanide failed to demonstrate promising activity against T. muris and A. ceylanicum in vivo, regardless whether tested as monotherapy or combined with standard drugs. Reasons for the discrepancy of these findings compared to results obtained in clinical trials remain to be elucidated.

L-arginine, a nitric oxide precursor, reduces dapsone-induced methemoglobinemia in rats

Dapsone use is frequently associated to hematological side effects such as methemoglobinemia and hemolytic anemia, which are related to N-hydroxylation mediated by the P450 enzyme system. The aim of the present study was to evaluate the influence of L-arginine supplementation, a precursor for the synthesis of nitric oxide, as single or multiple dose regimens on dapsone-induced methemoglobinemia. Male Wistar rats were treated with L-arginine at 5, 15, 30, 60 and 180 mg/kg doses (p.o., gavage) in single or multiple dose regimens 2 hours prior to dapsone administration (40 mg/kg, i.p.). The effect of the nitric oxide synthase inhibitor L-NAME was investigated by treatment with multiple doses of 30 mg/kg (p.o., gavage) 2 hours before dapsone administration. Blood samples were collected 2 hours after dapsone administration. Erythrocytic methemoglobin levels were assayed by spectrophotometry. The results showed that multiple dose supplementations with 5 and 15 mg/kg L-arginine reduced dapsone-induced methemoglobin levels. This effect is mediated by nitric oxide formation, since the reduction in methemoglobin levels by L-arginine is blocked by simultaneous administration with L-NAME, a nitric oxide synthase inhibitor.

A research agenda for malaria eradication: drugs

Antimalarial drugs will be essential tools at all stages of malaria elimination along the path towards eradication, including the early control or "attack" phase to drive down transmission and the later stages of maintaining interruption of transmission, preventing reintroduction of malaria, and eliminating the last residual foci of infection. Drugs will continue to be used to treat acute malaria illness and prevent complications in vulnerable groups, but better drugs are needed for elimination-specific indications such as mass treatment, curing asymptomatic infections, curing relapsing liver stages, and preventing transmission. The ideal malaria eradication drug is a coformulated drug combination suitable for mass administration that can be administered in a single encounter at infrequent intervals and that results in radical cure of all life cycle stages of all five malaria species infecting humans. Short of this optimal goal, highly desirable drugs might have limitations such as targeting only one or two parasite species, the priorities being Plasmodium falciparum and Plasmodium vivax. The malaria research agenda for eradication should include research aimed at developing such drugs and research to develop situation-specific strategies for using both current and future drugs to interrupt malaria transmission.

A research agenda to underpin malaria eradication

The interruption of malaria transmission worldwide is one of the greatest challenges for international health and development communities. The current expert view suggests that, by aggressively scaling up control with currently available tools and strategies, much greater gains could be achieved against malaria, including elimination from a number of countries and regions; however, even with maximal effort we will fall short of global eradication. The Malaria Eradication Research Agenda (malERA) complements the current research agenda--primarily directed towards reducing morbidity and mortality--with one that aims to identify key knowledge gaps and define the strategies and tools that will result in reducing the basic reproduction rate to less than 1, with the ultimate aim of eradication of the parasite from the human population. Sustained commitment from local communities, civil society, policy leaders, and the scientific community, together with a massive effort to build a strong base of researchers from the endemic areas will be critical factors in the success of this new agenda.

Pitfalls in new artemisinin-containing antimalarial drug development

Artemisinin combination therapy (ACT) paves the way for new opportunities to eliminate malaria in the tropics. However, the huge increase of ACT consumption raises major concerns about their availability over the next few years. At the same time a decrease in their efficacy has already been reported. Alongside the deployment of multifocal control programs, the process ranging from artemisia crop production to accreditation of new ACT combinations urgently needs to be strengthened to supply sufficient quantities of high-quality drugs. New suppliers will have the opportunity to enter this market to develop new formulations, and bioequivalence studies are required to validate these new formulations. It is thus crucial for national malaria control teams to be able to better scrutinize the dossier of these new formulations.

Mefloquine damage vestibular hair cells in organotypic cultures

Mefloquine is an effective and widely used anti-malarial drug; however, some clinical reports suggest that it can cause dizziness, balance, and vestibular disturbances. To determine if mefloquine might be toxic to the vestibular system, we applied mefloquine to organotypic cultures of the macula of the utricle from postnatal day 3 rats. The macula of the utricle was micro-dissected out as a flat surface preparation and cultured with 10, 50, 100, or 200 μM mefloquine for 24 h. Specimens were stained with TRITC-conjugated phalloidin to label the actin in hair cell stereocilia and TO-PRO-3 to visualize cell nuclei. Some utricles were also labeled with fluorogenic caspase-3, -8, or -9 indicators to evaluate the mechanism of programmed cell death. Mefloquine treatment caused a dose-dependent loss of utricular hair cells. Treatment with 10 μM caused a slight reduction, 50 μM caused a significant reduction, and 200 μM destroyed nearly all the hair cells. Hair cell nuclei in mefloquine-treated utricles were condensed and fragmented, morphological features of apoptosis. Mefloquine-treated utricles were positive for the extrinsic initiator caspase-8 and intrinsic initiator caspase-9 and downstream executioner caspase-3. These results indicate that mefloquine can induce significant hair cell degeneration in the postnatal rat utricle and that mefloquine-induced hair cell death is initiated by both caspase-8 and caspase-9.

Return of chloroquine-susceptible falciparum malaria in Malawi was a reexpansion of diverse susceptible parasites

The spread of drug-resistant Plasmodium falciparum malaria has been a major impediment to malaria control and threatens prospects for elimination. We recently demonstrated the return of chloroquine-susceptible malaria in Malawi after chloroquine use was abandoned. In this study, we trace the origins of chloroquine-resistant and chloroquine-susceptible parasites in Malawi by sequencing the P. falciparum chloroquine resistance transporter gene (pfcrt) and by genotyping microsatellites flanking this gene in isolates from infections that occurred in Malawi from 1992 through 2005. Malaria parasites from 2005 harbored the expected wild-type pfcrt haplotype associated with chloroquine susceptibility and have maintained high levels of diversity without linkage disequilibrium, which suggests that the return of chloroquine susceptibility is not the result of a back mutation in a formerly resistant parasite or a new selective sweep. Chloroquine-susceptible parasites that predominate in Malawi likely represent a reexpansion of the susceptible parasites that survived in the population despite widespread drug pressure in the region.

Is halofantrine ototoxic? Experimental study on guinea pig cochlea model

INTRODUCTION

Halofantrine is a newly developed antimalarial drug used for the treatment of Plasmodium falciparum malaria. The introduction of this drug has been delayed because of its possible side effects, and due to insufficient studies on adverse reactions in humans. There have been no studies investigating its effect on hearing.

METHODS

Thirty guinea pigs were divided into three groups: a control group, a halofantrine therapeutic dose group and a halofantrine double therapeutic dose group. One cochlea specimen from each animal was stained with haematoxylin and eosin and the other with toluidine blue.

RESULTS

No changes were detected in the control group. The halofantrine therapeutic dose group showed loss and distortion of inner hair cells and inner phalangeal cells, and loss of spiral ganglia cells. In the halofantrine double therapeutic dose group, the inner and outer hair cells were distorted and there was loss of spiral ganglia cells.

CONCLUSION

Halofantrine has mild to moderate pathological effects on cochlea histology, and can be considered an ototoxic drug.

Monitoring antimalarial drug efficacy: current challenges

Access to effective antimalarial therapy has increased dramatically. As malaria-endemic countries begin to use artemisinin-based combination therapy (ACT) to treat malaria, detecting the emergence and spread of resistance has become more complicated but also more urgent. Clinical efficacy studies may not be sensitive enough to detect the failure of a single component of combination therapy while standardized criteria for in vitro resistance and validated molecular markers are not yet available to many currently deployed drugs. This review discusses the challenges to various methods to monitor antimalarial drug resistance and proposes an integrated approach to the rapid detection and characterization of resistance to ACTs should it arise.

Population pharmacokinetics and pharmacodynamic considerations of amodiaquine and desethylamodiaquine in Kenyan adults with uncomplicated malaria receiving artesunate-amodiaquine combination therapy

Amodiaquine (AQ) is an antimalarial drug that was frequently combined with artesunate (AS) for the treatment of uncomplicated malaria due to Plasmodium falciparum and is now available as a fixed-dose combination. Despite its widespread use, the simultaneous pharmacokinetics in patients of AQ and its active metabolite, desethylamodiaquine (DAQ), were not characterized to date. The pharmacokinetics of AQ and DAQ in 54 adult patients receiving the AS/AQ combination were therefore investigated by the use of a population approach. AQ followed a 1-compartment model with first-order absorption and elimination, as well as a first-order and irreversible transformation into DAQ, which in turn followed a 2-compartment model with first-order elimination from its central compartment. The mean AQ apparent clearance and distribution volume were 3,410 liters/h and 39,200 liters, respectively. The mean terminal elimination half-life of DAQ was 211 h. Body weight was found to explain the interindividual variability of the apparent volume of distribution of AQ and the elimination rate constant of DAQ. A new dosage form consisting of a fixed-dose combination of AS and AQ was found to have no effect on the pharmacokinetic parameters of AQ and DAQ. All patients achieved parasite clearance within 4 days following the initiation of the treatment, which prevented investigation of the possible relationship between DAQ exposure and treatment outcome. This study provided the first simultaneous pharmacokinetic model for AQ and DAQ.

Resistance to antimalarial drugs: molecular, pharmacologic, and clinical considerations

One of the greatest obstacles to the control of malaria has been the spread of resistance to drugs used on a large scale. This review provides an update of the current understanding of the molecular basis for antimalarial drug resistance. Parasite intrinsic resistance is just one component that determines the in vivo efficacy of a drug. Human immune responses and pharmacologic properties play important roles in determining the clinical outcome of treatment. The emergence and spread of resistance also results from an interplay of these factors. Current efforts to characterize and deter resistance to new combination therapy are also discussed.

Availability and choice of antimalarials at medicine outlets in Ghana: the question of access to effective medicines for malaria control

Although national and international efforts to combat malaria have intensified over the years, problems with availability, distribution, and choice of antimalarials at medicine outlets in Africa continue to exist. This article presents the results of an indicator-based assessment of availability and choice of antimalarials at 130 licensed medicine outlets in Ghana. We also discuss how the choice of an antimalarial to dispense conforms to recommendations of the national policy for malaria therapy. Data were obtained through face-to-face interviews, by reviewing facility records, and by observing the practices of dispensing staff in the medicine outlets. Antimalarials recommended in the policy were not readily available in the most accessible medicine outlets. Few outlets adhered to the policy when choosing antimalarials. Interventions targeting medicine outlets should be initiated to improve availability and access to effective medicines in order to support the national program for malaria control.