Comparison of artemether and chloroquine for severe malaria in Gambian children

Origin and Spread of Evolving Artemisinin-Resistant Plasmodium falciparum Malarial Parasites in Southeast Asia

In this review, we provide an epidemiological history of the emergence and ongoing spread of evolving Plasmodium falciparum artemisinin resistance (ARTR). Southeast Asia has been the focal point for emergence and spread of multiple antimalarial drug resistance phenomena, and is once again for evolving ARTR, also known as the "delayed clearance phenotype" (DCP). The five countries most impacted, Cambodia, Thailand, Myanmar, Laos, and Vietnam, each have complex histories of antimalarial drug use over many decades, which have in part molded the use of various artemisinin combination therapies (ACTs) within each country. We catalog the use of ACTs, evolving loss of ACT efficacy, and the frequency of pfk13 mutations (mutations associated with ARTR) in the Greater Mekong Subregion and map the historical spread of ARTR/DCP parasites. These data should assist improved surveillance and deployment of next-generation ACTs.

Artemether for severe malaria

BACKGROUND

In 2011 the World Health Organization (WHO) recommended parenteral artesunate in preference to quinine as first-line treatment for people with severe malaria. Prior to this recommendation many countries, particularly in Africa, had begun to use artemether, an alternative artemisinin derivative. This Cochrane Review evaluates intramuscular artemether compared with both quinine and artesunate.

OBJECTIVES

To assess the efficacy and safety of intramuscular artemether versus any other parenteral medication in the treatment of severe malaria in adults and children.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (the Cochrane Library), MEDLINE, Embase, and LILACS, ISI Web of Science, conference proceedings, and reference lists of articles. We also searched the WHO International Clinical Trial Registry Platform, ClinicalTrials.gov, and the metaRegister of Controlled Trials (mRCT) for ongoing trials up to 7 September 2018. We checked the reference lists of all studies identified by the search. We examined references listed in review articles and previously compiled bibliographies to look for eligible studies.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing intramuscular artemether with intravenous/intramuscular quinine or artesunate for treating severe malaria.

DATA COLLECTION AND ANALYSIS

The primary outcome was all-cause death. Two review authors independently screened each article by title and abstract, and examined potentially relevant studies for inclusion using an eligibility form. Two review authors independently extracted data and assessed risk of bias of included studies. We summarized dichotomous outcomes using risk ratios (RRs) and continuous outcomes using mean differences (MDs), and have presented both measures with 95% confidence intervals (CIs). Where appropriate, we combined data in meta-analyses and used the GRADE approach to summarize the certainty of the evidence.

MAIN RESULTS

We included 19 RCTs, enrolling 2874 adults and children with severe malaria, carried out in Africa (12 trials) and in Asia (7 trials).Artemether versus quinineFor children, there is probably little or no difference in the risk of death between intramuscular artemether and quinine (RR 0.97, 95% CI 0.77 to 1.21; 13 trials, 1659 participants, moderate-certainty evidence). Coma resolution time may be about five hours shorter with artemether (MD -5.45, 95% CI -7.90 to -3.00; six trials, 358 participants, low-certainty evidence). Artemether may make little difference to neurological sequelae (RR 0.84, 95% CI 0.66 to 1.07; seven trials, 968 participants, low-certainty evidence). Compared to quinine, artemether probably shortens the parasite clearance time by about nine hours (MD -9.03, 95% CI -11.43 to -6.63; seven trials, 420 participants, moderate-certainty evidence), and may shorten the fever clearance time by about three hours (MD -3.73, 95% CI -6.55 to -0.92; eight trials, 457 participants, low-certainty evidence).For adults, treatment with intramuscular artemether probably results in fewer deaths than treatment with quinine (RR 0.59, 95% CI 0.42 to 0.83; four trials, 716 participants, moderate-certainty evidence).Artemether versus artesunateArtemether and artesunate have not been directly compared in randomized trials in children.For adults, mortality is probably higher with intramuscular artemether (RR 1.80, 95% CI 1.09 to 2.97; two trials, 494 participants, moderate-certainty evidence).

AUTHORS' CONCLUSIONS

Artemether appears to be more effective than quinine in children and adults. Artemether compared to artesunate has not been extensively studied, but in adults it appears inferior. These findings are consistent with the WHO recommendations that artesunate is the drug of choice, but artemether is acceptable when artesunate is not available.

A Brief History of Qinghaosu

The 2015 Nobel Prize for Medicine or Physiology was awarded to William C. Campbell and Satoshi Ōmura for their discovery of avermectins, and to Tu You You for her contribution to the discovery of artemisinin. The discovery and development of qinghaosu (artemisinin) as an antimalarial drug is a remarkable and convoluted tale.

Artemether for severe malaria

BACKGROUND

In 2011 the World Health Organization (WHO) recommended parenteral artesunate in preference to quinine as first-line treatment for people with severe malaria. Prior to this recommendation, many countries, particularly in Africa, had begun to use artemether, an alternative artemisinin derivative. This review evaluates intramuscular artemether compared with both quinine and artesunate.

OBJECTIVES

To assess the efficacy and safety of intramuscular artemether versus any other parenteral medication in treating severe malaria in adults and children.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (The Cochrane Library), MEDLINE, EMBASE and LILACS, ISI Web of Science, conference proceedings and reference lists of articles. We also searched the WHO clinical trial registry platform, ClinicalTrials.gov and the metaRegister of Controlled Trials (mRCT) for ongoing trials up to 9 April 2014.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing intramuscular artemether with intravenous or intramuscular antimalarial for treating severe malaria.

DATA COLLECTION AND ANALYSIS

The primary outcome was all-cause death.Two authors independently assessed trial eligibility, risk of bias and extracted data. We summarized dichotomous outcomes using risk ratios (RR) and continuous outcomes using mean differences (MD), and presented both measures with 95% confidence intervals (CI). Where appropriate, we combined data in meta-analyses and assessed the quality of the evidence using the GRADE approach.

MAIN RESULTS

We included 18 RCTs, enrolling 2662 adults and children with severe malaria, carried out in Africa (11) and in Asia (7). Artemether versus quinine For children in Africa, there is probably little or no difference in the risk of death between intramuscular artemether and quinine (RR 0.96, 95% CI 0.76 to 1.20; 12 trials, 1447 participants, moderate quality evidence). Coma recovery may be about five hours shorter with artemether (MD -5.45, 95% CI -7.90 to -3.00; six trials, 358 participants, low quality evidence), and artemether may result in fewer neurological sequelae, but larger trials would be needed to confirm this (RR 0.84, 95% CI 0.66 to 1.07; seven trials, 968 participants, low quality evidence). Artemether probably shortens the parasite clearance time by about nine hours (MD -9.03, 95% CI -11.43 to -6.63; seven trials, 420 participants, moderate quality evidence), and may shorten the fever clearance time by about three hours (MD -3.73, 95% CI -6.55 to -0.92; eight trials, 457 participants, low quality evidence).For adults in Asia, treatment with intramuscular artemether probably results in fewer deaths than treatment with quinine (RR 0.59, 95% CI 0.42 to 0.83; four trials, 716 participants, moderate quality evidence). Artemether versus artesunate Artemether and artesunate have not been directly compared in randomized trials in African children.For adults in Asia, mortality is probably higher with intramuscular artemether (RR 1.80, 95% CI 1.09 to 2.97, two trials,494 participants, moderate quality evidence).

AUTHORS' CONCLUSIONS

Although there is a lack of direct evidence comparing artemether with artesunate, artemether is probably less effective than artesunate at preventing deaths from severe malaria. In circumstances where artesunate is not available, artemether is an alternative to quinine.

Clinical features and outcome in children with severe Plasmodium falciparum malaria: a meta-analysis

Background

Although global malaria mortality is declining, estimates may not reflect better inpatient management of severe malaria (SM) where reported case fatality rates (CFRs) vary from 1–25%.

Methods

A meta-analysis of prospective studies of SM was conducted to examine i) whether hypothesized differences between clinical features and outcome in Melanesian compared with African or Asian children really exist, and ii) to explore temporal changes in overall and complication-specific CFRs. The proportions of different SM complications and, overall and complication-specific CFRs were incorporated into the meta-analysis. Adjustments were made for study-level covariates including geographic region, SM definition, artemisinin treatment, median age of participants and time period.

Findings

Sixty-five studies were included. Substantial heterogeneity (I²>80%) was demonstrated for most outcomes. SM definition contributed to between-study heterogeneity in proportions of cerebral malaria (CM), metabolic acidosis (MA), severe anemia and overall CFR, whilst geographic region was a significant moderator in for CM and hypoglycemia (HG) rates. Compared with their African counterparts, Melanesian children had lower rates of HG (10% [CI95 7–13%] versus 1% [0–3%], P<0.05), lower overall CFR (2% [0–4%] versus 7% [6–9%], P<0.05) and lower CM-specific CFR (8% [0–17%] versus 19% [16–21%], P<0.05). There was no temporal trend for overall CFR and CM-specific CFR but declining HG- and MA- specific CFRs were observed.

Interpretation

These data highlight that recent estimates of declining global malaria mortality are not replicated by improved outcomes for children hospitalized with SM. Significant geographic differences in the complication rates and subsequent CFRs exist and provide the first robust confirmation of lower CFRs in Melanesian children, perhaps due to less frequent HG.

Antimalarial drug resistance: a review of the biology and strategies to delay emergence and spread

The emergence of resistance to former first-line antimalarial drugs has been an unmitigated disaster. In recent years, artemisinin class drugs have become standard and they are considered an essential tool for helping to eradicate the disease. However, their ability to reduce morbidity and mortality and to slow transmission requires the maintenance of effectiveness. Recently, an artemisinin delayed-clearance phenotype was described. This is believed to be the precursor to resistance and threatens local elimination and global eradication plans. Understanding how resistance emerges and spreads is important for developing strategies to contain its spread. Resistance is the result of two processes: (i) drug selection of resistant parasites; and (ii) the spread of resistance. In this review, we examine the factors that lead to both drug selection and the spread of resistance. We then examine strategies for controlling the spread of resistance, pointing out the complexities and deficiencies in predicting how resistance will spread.

Features and prognosis of severe malaria caused by Plasmodium falciparum, Plasmodium vivax and mixed Plasmodium species in Papua New Guinean children

Background

Mortality from severe pediatric falciparum malaria appears low in Oceania but Plasmodium vivax is increasingly recognized as a cause of complications and death. The features and prognosis of mixed Plasmodium species infections are poorly characterized. Detailed prospective studies that include accurate malaria diagnosis and detection of co-morbidities are lacking.

Methods and Findings

We followed 340 Papua New Guinean (PNG) children with PCR-confirmed severe malaria (77.1% P. falciparum, 7.9% P. vivax, 14.7% P. falciparum/vivax) hospitalized over a 3-year period. Bacterial cultures were performed to identify co-incident sepsis. Clinical management was under national guidelines. Of 262 children with severe falciparum malaria, 30.9%, 24.8% and 23.2% had impaired consciousness, severe anemia, and metabolic acidosis/hyperlactatemia, respectively. Two (0.8%) presented with hypoglycemia, seven (2.7%) were discharged with neurologic impairment, and one child died (0.4%). The 27 severe vivax malaria cases presented with similar phenotypic features to the falciparum malaria cases but respiratory distress was five times more common (P = 0.001); one child died (3.7%). The 50 children with P. falciparum/vivax infections shared phenotypic features of mono-species infections, but were more likely to present in deep coma and had the highest mortality (8.0%; P = 0.003 vs falciparum malaria). Overall, bacterial cultures were positive in only two non-fatal cases. 83.6% of the children had alpha-thalassemia trait and seven with coma/impaired consciousness had South Asian ovalocytosis (SAO).

Conclusions

The low mortality from severe falciparum malaria in PNG children may reflect protective genetic factors other than alpha-thalassemia trait/SAO, good nutrition, and/or infrequent co-incident sepsis. Severe vivax malaria had similar features but severe P. falciparum/vivax infections were associated with the most severe phenotype and worst prognosis.

Randomised trial of artemether versus artemether and mefloquine for the treatment of chloroquine/sufadoxine-pyrimethamine-resistant falciparum malaria during pregnancy

The efficacy of artemether and artemether followed by mefloquine was evaluated in 45 pregnant women with drug resistant Plasmodium falciparum malaria during the second and third trimesters. There was prompt clinical response to both treatment regimens. The parasite and fever clearance times and the cure rate were similar in both groups. Except for the correlation between initial parasite density and fever clearance time in the artemether-mefloquine group, there was no correlation between initial parasite density and parasite or fever clearance times in the two groups. Similarly, there was no correlation between parasite and fever clearance. Both treatment regimens were well tolerated. All newborn babies of the participating women were normal at birth. Physical and neurodevelopmental assessment of the newborn babies followed up for a period varying between 6 and 36 months were within normal limits. Artemether alone or with mefloquine are effective and do not produce undue deleterious effects in pregnant patients with drug-resistant falciparum malaria during the second and third trimesters.

Dietary supplement labeling: cognitive biases, market manipulation & consumer choice

There exists increasing concern that the Dietary Supplements Health and Education Act (“DSHEA”) has proven ineffective and perhaps counterproductive. Most illustratively, consider a recent and remarkably candid remark from Tommy Thompson, then Secretary of Health and Human Services: “I really think Congress should take a look at the food supplement law again.It doesn't make any sense to me.”

A health law that makes no sense to the Secretary of Health of Health and Human Services should certainly draw the attention of academics and policy-makers alike. Much of the debate concerning DSHEA regards the disparity in legislative treatment between dietary supplements, foods, and pharmaceutical drugs. Specifically, while pharmaceutical drugs must undergo years of costly pre-market testing, most dietary supplements—like most foods—can immediately enter the market, and only after repeated instances of adverse reactions can the Food and Drug Administration (“FDA”) remove them.

[Treatment of children with malaria Plasmodium falciparum with derivatives artemisinin]

From January 1996 to December 1998, artemisinin derivatives were prescribed to 108 children infected with Plasmodium falciparum. The therapeutic effect was evaluated. Only children with moderate or severe malaria were included. Group I (intravenous artesunate; n = 62): 50.8% with moderate malaria and 49.2% with severe malaria; 53.2% with mild parasitemia, 22.6% with moderate parasitemia and 24.2% with high parasitemia; Group II (intramuscular artemether [Paluter ]; n = 46): 67.4% with moderate malaria and 32.6% with severe malaria; 52.2% with mild parasitemia, 36.2% with moderate parasitemia and 15.2% with high parasitemia; clinical amelioration and clearance of parasitemia showed no statistical difference between the groups. All patients cleared the parasitemia at the seventh day of follow-up (D7). In order to avoid recrudescence, mefloquine or clindamycin was used.

Artemisinin or chloroquine for blood stage Plasmodium vivax malaria in Vietnam

Chloroquine-resistant Plasmodium vivax has not yet occurred in Vietnam. The efficacy of artemisinin for P. vivax was not established. We conducted a double-blind randomized study involving 240 inpatients with P. vivax malaria who received artemisinin (40 mg/kg over 3 days) plus placebo chloroquine (Art) or chloroquine (25 mg/kg over 3 days) plus placebo artemisinin (Chl). Patients were followed up with weekly blood smears for 28 days. In each group 113 cases were analysed. All patients recovered rapidly. The median (range) parasite clearance time of regimen Art was 24 h (8-72) and of Chl 24 h (8-64; P = 0.3). Parasites reappeared in two cases in each group on day 14, in eight cases in each group (7%) on day 16 and in 25 (23%) and 18 (16%) cases, respectively, at the end of 4-week follow-up (P = 0.3). The population parasite clearance curve followed a mono-exponential decline. The parasite reduction ratio per 48 h reproduction cycle was 2.3 x 104 for both regimens. We conclude that artemisinin and chloroquine are equally effective in the treatment of P. vivax infections in Vietnam. Reappearance of parasites before day 16 (7%) suggests the emergence of chloroquine resistance. Three days of artemisinin monotherapy does not prevent recrudescence.

Pharmacokinetic interactions of antimalarial agents

Combination of antimalarial agents has been introduced as a response to widespread drug resistance. The higher number of mutations required to express complete resistance against combinations may retard the further development of resistance. Combination of drugs, especially with the artemisinin drugs, may also offer complete and rapid eradication of the parasite load in symptomatic patients and thus reduce the chance of survival of resistant strains. The advantages of combination therapy should be balanced against the increased chance of drug interactions. During the last decade, much of the pharmacokinetics and metabolic pathways of antimalarial drugs have been elucidated, including the role of the cytochrome P450 (CYP) enzyme complex. Change in protein binding is not a significant cause of interactions between antimalarial agents. CYP3A4 and CYP2C19 are frequently involved in the metabolism of antimalarial agents. Quinidine is a potent inhibitor of CYP2D6, but it appears that this enzyme does not mediate the metabolism of any other antimalarial agent. The new combinations proguanil-atovaquone and chlorproguanil-dapsone do not show significant interactions. CYP2B6 and CYP3A4 are involved in the metabolism of artemisinin and derivatives, but further studies may reveal involvement of more enzymes. Artemisinin may induce CYP2C19. Several artemisinin drugs suffer from auto-induction of the first-pass effect, resulting in a decline of bioavailability after repeated doses. The mechanism of this effect is not yet clear, but induction by other agents cannot be excluded. The combination of artemisinin drugs with mefloquine and the fixed combination artemether-lumefantrine have been studied widely, and no significant drug interactions have been found. The artemisinin drugs will be used at an increasing rate, particularly in combination with other agents. Although clinical studies have so far not shown any significant interactions, drug interactions should be given appropriate attention when other combinations are used.

Artemisinin derivatives for treating severe malaria

BACKGROUND

Artemisinin derivatives may have advantages over quinoline drugs for treating severe malaria since they are fast acting and effective against quinine resistant malaria parasites.

OBJECTIVES

The objective of this review was to assess the effects of artemisinin drugs for severe and complicated falciparum malaria in adults and children.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group trials register, Cochrane Controlled Trials Register, Medline, Embase, Science Citation Index, Lilacs, African Index Medicus, conference abstracts and reference lists of articles. We contacted organisations, researchers in the field and drug companies.

SELECTION CRITERIA

Randomised and pseudo-randomised trials comparing artemisinin drugs (rectal, intramuscular or intravenous) with standard treatment, or comparisons between artemisinin derivatives in adults or children with severe or complicated falciparum malaria.

DATA COLLECTION AND ANALYSIS

Eligibility, trial quality assessment and data extraction were done independently by two reviewers. Study authors were contacted for additional information.

MAIN RESULTS

Twenty three trials are included, allocation concealment was adequate in nine. Sixteen trials compared artemisinin drugs with quinine in 2653 patients. Artemisinin drugs were associated with better survival (mortality odds ratio 0.61, 95% confidence interval 0.46 to 0.82, random effects model). In trials where concealment of allocation was adequate (2261 patients), this was barely statistically significant (odds ratio 0.72, 95% CI 0.54 to 0.96, random effects model). In 1939 patients with cerebral malaria, mortality was also lower with artemisinin drugs overall (odds ratio 0.63, 95% CI 0.44 to 0.88, random effects model). The difference was not significant however when only trials reporting adequate concealment of allocation were analysed (odds ratio 0.78, 95% CI 0.55 to 1.10, random effects model) based on 1607 patients. No difference in neurological sequelae was shown. Compared with quinine, artemisinin drugs showed faster parasite clearance from the blood and similar adverse effects.

REVIEWER'S CONCLUSIONS

The evidence suggests that artemisinin drugs are no worse than quinine in preventing death in severe or complicated malaria. No artemisinin derivative appears to be better than the others.

Distinction of recrudescences from new infections by PCR-RFLP analysis in a comparative trial of CGP 56 697 and chloroquine in Tanzanian children

OBJECTIVE

To test the efficacy of a new compound drug (CGP 56697) against acute, uncomplicated falciparum malaria.

METHOD

Reappearing parasites were analysed by PCR-RFLP within a randomized controlled trial. 130 patients received chloroquine and 130 patients were treated with CGP 56697. Samples from 96 patients with parasitological failure were tested by PCR-RFLP for MSP2 of Plasmodium falciparum. Seven days after treatment 32 patients of the chloroquine control group with reappearing parasites were tested by PCR and one infection was unequivocally determined as a new infection. After 7 days, in the CGP 56697 group, 6 samples were tested in which one new infection was identified. Similar observations were made one and three weeks later in both groups.

RESULTS

Although a high multiplicity of infections on admission was observed, there was no significant correlation between multiplicity and either recrudescence or new infection. Patients in both treatment groups with subsequent recrudescent parasites had higher initial mean parasite densities than patients who cleared. Those of the patients with recrudescent parasites who were treated with CGP 56697 had higher initial parasite densities than those treated with chloroquine. The rate of re-infection increased with time as expected in holoendemic areas and appeared to be higher in chloroquine patients. Generally, CGP 56697 showed a superior clearance rate, successfully cleared higher parasite densities and suppressed new infections over a longer period of time.

CONCLUSION

The PCR analysis confirmed that reinfections beyond day 7 are significant in areas highly endemic for malaria and showed the necessity of excluding these when estimating 14 day clearance rates. Provided new infections are excluded, the 28-day clearance rate can also be used to determine the efficacy of antimalarial drugs in highly endemic areas, and adds to our knowledge of drug resistance and dynamics of infections in people living in such areas.

alpha, beta-Arteether for the treatment of complicated falciparum malaria

alpha, beta-Arteether is an ethyl ether derivative of artemisinin which is an efficient schizontocidal drug in mild falciparum malaria. The present study reports the efficacy of the drug in severe falciparum malaria. Fifty patients with severe falciparum malaria were given intramuscular arteether, 150 mg, once daily on 3 consecutive days. The median fever clearance time was 72 h (range 12-120 h) and the median parasite clearance time was 2 d (range 1-4 d). Rapid recovery from coma was observed in cerebral malaria patients (after a median of 18 h, range 6-72 h). The recovery from other complications was also faster and complete. Two patients died; both had cerebral malaria and haemolytic jaundice, one had respiratory distress needing ventilatory support and the other had severe anaemia. Recrudescence within 28 d was observed in 7 patients. Drug toxicity or significant side effects were not noticed in any patient.

Malaria

The preeminent infectious threat to unwary tropical travelers, malaria is a preventable, mosquito-borne protozoan infection of red blood cells, which causes fever, anemia, respiratory failure, coma, and death. Malaria is a true medical emergency that requires rapid diagnosis and treatment. Unfortunately, in two thirds of tropical travelers who die of malaria, either treatment is delayed or the diagnosis is simply missed. Every tropical traveler with fever or unexplained, flu-like illness must be assumed to have life-threatening malaria and must have thick and thin blood smears immediately examined to confirm the diagnosis.

Clinical pharmacology and therapeutic potential of artemisinin and its derivatives in the treatment of malaria

Artemisinin and its derivatives are renowned for their potent antimalarial activity. They have found their way into clinical use in many areas where malaria is endemic. The in vitro concentration at which artemisinin can inhibit 50% of the growth of Plasmodium falciparum ranges from 3 to 30 micrograms/L. The fat-soluble derivatives artemether and arteether are approximately twice as active. The water-soluble dihydro-artemisinin and artesunate are 4 to 5 times more active in vitro. Artemisinin is available only for oral and rectal administration. Absorption is incomplete and elimination is fast, with and elimination half-life of 2 to 5 hours. Plasma concentrations after a single 500 mg oral dose most often exceed 200 micrograms/L. Artesunate and artemether can be considered as prodrugs. Biotransformation into the active metabolite dihydro-artemisinin occurs rapidly--almost immediately for artesunate. The reported elimination half-life of artesunate is less than 1 hour, and for artemether the figure is 3 to 11 hours. The pharmacokinetics of dihydro-artemisinin are not yet completely clear. Elimination is probably also rapid, with an elimination half-life of a few hours. Arteether, dissolved in oil for intramuscular administration, has a much longer elimination half-life of over 20 hours. The clinical efficacy of this group of drugs is characterised by an almost immediate onset and rapid reduction of parasitaemia, with complete clearance in most cases within 48 hours. Efficacy is high even in areas with multidrug-resistant parasite strains. To prevent recrudescence with monotherapy of these compounds, treatment needs to be extended beyond the disappearance of parasites. After 5 days of therapy the rate of recrudescence is approximately 10%. Alternatively, combination with other drugs can be used. Combination with mefloquine is recommended for areas with multidrug-resistant P. falciparum.

Artemisinin and the antimalarial endoperoxides: from herbal remedy to targeted chemotherapy

Artemisinin and its derivatives are endoperoxide-containing compounds which represent a promising new class of antimalarial drugs. In the presence of intraparasitic iron, these drugs are converted into free radicals and other electrophilic intermediates which then alkylate specific malaria target proteins. Combinations of available derivatives and other antimalarial agents show promise both as first-line agents and in the treatment of severe disease.

Therapeutic effects of chloroquine in combination with quinine in uncomplicated falciparum malaria

The efficacy and toxicity of oral quinine combined with oral chloroquine were studied in 50 Thai men with uncomplicated falciparum malaria. All were treated for 7 days with quinine sulphate (10 mg salt/kg every 8 h). Twenty-five of the patients, selected at random, were also given oral tetracycline (4 mg/kg four times daily) over the same period and the remainder were given chloroquine (25 mg base/kg over the first 3 days). There were no serious adverse effects. Overall fever-clearance times (FCT) and parasite-clearance times (PCT) in the chloroquine and tetracycline groups were not significantly different, with mean (S.D.) values of 51 (33) and 41 (27) h for FCT and 80 (25) and 83 (21) h for PCT, respectively. Most of the patients (18 in each group) were followed for > or = 2 months. Recrudescence rates (R1) were significantly higher in the chloroquine group than in the tetracycline group (39% v. 6%; P = 0.02), all recrudescences occurring within 4 weeks (18-25 days) of starting treatment. Subsequent parasitaemia with Plasmodium vivax, however, occurred less frequently in the chloroquine group (11%) than in the tetracycline group (33%) (P = 0.11) and took longer to develop in the chloroquine group [51 or 59 days compared with a mean (S.D.) value of 29 (10) days in the tetracycline group; P = 0.01]. Within the chloroquine group, FCT and PCT were both shorter in those with cure than in those with R1 resistance, with mean (S.D.) values of 41 (25) and 70 (33) h for FCT (P = 0.09) and 72 (20) and 100 (18) h for PCT (P = 0.01), respectively. Chloroquine does not potentiate the clinical response to quinine against resistant strains of uncomplicated falciparum malaria, nor does it convey any useful antipyretic effect.

An open randomized trial of artemether versus quinine in the treatment of cerebral malaria in African children

We have compared the efficacy of artemether versus quinine as treatment for cerebral malaria in children in an open randomized clinical trial in Kenya. Children admitted to hospital with coma and Plasmodium falciparum parasitaemia were treated with either intramuscular artemether (3.2 mg/kg loading dose followed by 1.6 mg/kg daily) or intravenous quinine (20 mg/kg loading dose followed by 10 mg/kg every 8 h). Both drugs were well tolerated and no significant adverse effect was observed. Parasite clearance times (50% and 90%) were shorter in patients treated with artemether (median times [h], with interquartile ranges in brackets, were: 50%, 7.3 [4.2-12.4] vs. 15.5 [9-22]; 90%, 16.9 [13.2-25] vs. 28.5 [22-35]; P < 0.0001). The total mortality in 160 children with cerebral malaria was 16.25%, with no overall significant difference between the 2 treatment groups. In a subgroup of children with respiratory distress, mortality was higher in those treated with artemether (43.7% vs. 11.1%, P < 0.05). The frequency of neurological sequelae and clinical recovery times were similar in both treatment groups. We conclude that there would currently be no advantage in replacing quinine with artemether for the treatment of cerebral malaria in African children.

In vitro stage-specific sensitivity of Plasmodium falciparum to quinine and artemisinin drugs

The inhibitory effects of quinine, chloroquine and 4 qinghaosu drugs, artemisinin, artemether, artesunate and dihydroartemisinin, on 4 culture-adapted isolates and 2 standard clones of Plasmodium falciparum were determined in vitro. All isolates were sensitive to the widely used antimalarial drugs quinine (EC50 range 3 x 10(-8)-1 x 10(-7) mol/L) and chloroquine (EC50 range 1 x 10(-9)-7 x 10(-9) mol/L), irrespective of the geographical origin or treatment history of the patients from which they were taken. In general, the qinghaosu drugs were more potent than the conventional antimalarials, having EC50 values of 3 x 10(-11)-3 x 10(-8) mol/L. Stage-specific data indicated that quinine has a primary mode of action on mature parasite forms, achieving 80-100% growth inhibition within 2-4 h of drug exposure. The stage-specific activity of the 3 qinghaosu drugs artemisinin, artemether and dihydroartemisinin differed from that of quinine, and each derivative displayed a unique stage-specific profile. Artemisinin was rapidly effective against both rings and schizonts, achieving 100% growth inhibition within 6-8 h. The inhibitory effects of artemether were less rapid, requiring 10 h to achieve 70-80% ring stage growth inhibition. Dihydroartemisinin was highly effective against all parasite stages in most cases achieving 100% growth inhibition within 2-4 h of exposure. The results confirm that the qinghaosu drugs are potent antimalarials, and suggest different stage-specific profiles compared to conventional antimalarial drugs.

Renal function in acute falciparum malaria

Renal function was assessed in 40 children during the acute illness and after recovery from falciparum malaria. Creatinine clearance was significantly lower during the acute illness than after recovery. Six of 18 children with impaired creatinine clearance (< 50 ml/min/1.73 m2) had evidence of acute tubular dysfunction. Hyponatraemia occurred in 12.5% during the acute phase. Fractional sodium excretion was raised in 27% during the acute illness and continuing sodium wastage occurred in 17% after recovery. Plasma potassium was significantly higher and fractional potassium excretion (FeK) significantly lower during the acute illness than after recovery. There was a positive correlation between FeNa and FeK both during and after recovery from the illness but they did not exactly mirror each other in every individual. Urine sodium:potassium ratios were similar during and after recovery from the illness and was related to FeNa. Fractional glucose excretion was zero. Mild proteinuria occurred in 40% during the acute illness but were not related to creatinine clearance, body temperature at presentation, or peripheral parasite density. Proteinuria was absent after recovery. Acute intrinsic renal impairment occurs during apparently 'uncomplicated' falciparum malaria in children.

Open comparison of artemether and mefloquine in uncomplicated Plasmodium falciparum hyperparasitaemia in children

The efficacy of intramuscular artemether given for 5 days and a single oral dose of mefloquine, 25 mg/kg/body-weight, was evaluated in 84 children with uncomplicated Plasmodium falciparum hyperparasitaemia ( > 5% parasitized erythrocytes). Follow-up was for 14 days in the artemether group and 28 days in the mefloquine group. Artemether produced a significantly higher parasite reduction at 24 hours [mean 90.6 vs 63.3%, 95% confidence interval 10.7-43.9] and significantly shorter parasite clearance time [mean 38.4 vs 49.3 hours, 95% confidence interval 5.5-16.3] than mefloquine. Fever clearance times were similar, presumably because of the use of an antipyretic in both treatment groups. Cure rate was 98% with artemether on day 14 and 100% with mefloquine on day 28. One child in the artemether group who had recurrence of parasitaemia on day 14 responded promptly to mefloquine with clearance of parasitaemia and fever at 24 hours. Although both drugs were well tolerated, mefloquine produced more episodes of abdominal pain with or without diarrhoea and vomiting. These results suggest that both drugs are effective in uncomplicated Plasmodium falciparum hyperparasitaemia in children from an endemic area of south-west Nigeria.

Efficacy of artemether in severe falciparum malaria in African children

The clinical efficacy of intramuscular artemether was studied in 144 children suffering from severe non cerebral malaria. Fifty-three children with chloroquine-resistant and 27 children with sulfadoxinepyrimethamine-resistant falciparum malaria were also studied. Greater than 95% of pre-treatment parasitaemia was cleared by 24 h after commencement of treatment in all groups. The parasite and fever clearance times were 35.4 +/- 8.0 and 18.6 +/- 6.3 h respectively, in children suffering from severe non cerebral malaria 36.3 +/- 7.9 and 15.6 +/- 3.8 h, respectively, in the chloroquine-resistant and 36.8 +/- 8.8 and 16.5 +/- 4.2 h, respectively, in the sulfadoxine-pyrimethamine-resistant groups. The cure rate in all groups on day 14 was 100%. Side effects following treatment were minimal and comprised pain with mild tenderness at site of injection in two children and bradycardia, on the second or third day of treatment, in another two patients. No patient had pruritus. These data suggest that artemether is rapidly effective in falciparum malaria in children irrespective of previous drug treatment and especially in chloroquine- or sulphadoxinepyrimethamine-resistant infection and in this study was without deleterious side effects.

Chemotherapy of drug-resistant malaria

OBJECTIVE

To review the impact of drug-resistant malaria on current management of plasmodial infections.

DATA SOURCES

A MEDLINE search of the English-language medical literature from 1985 to 1995; bibliographies of selected papers; international malaria advisory experts.

DATA SYNTHESIS

Combinations of artemisinin derivatives and mefloquine or atovaquone plus proguanil appear to be the most active drug regimens against multidrug-resistant falciparum malaria from Southeast Asia. The optimal therapy for chloroquine-resistant Plasmodium vivax is unknown, but recent data indicate that halofantrine or chloroquine plus high doses of primaquine are efficacious.

CONCLUSIONS

The incidence of drug-resistant malaria continues to increase at a rate that exceeds new drug development. Ultimately the control of malaria will require more creative approaches than just the development of additional inhibitory drugs. These might include the identification of biochemical pathways unique to the parasite (such as drug efflux and heme polymerization), making it possible to design new classes of antimalarial agents that are selectively toxic to the parasite; methods to block parasite development in the mosquito vector; and multistage vaccines against asexual and sexual stages to block both the pathophysiology and the transmission of disease.

Comparison of artemether and quinine in the treatment of severe falciparum malaria in south-east Thailand

One hundred and two Thai patients with severe falciparum malaria (92 males and 10 females) were allocated at random to receive either the standard regimen of quinine infusion (52 cases) or intramuscular artemether (50 cases). The patients in both groups had comparable admission clinical and laboratory data. Artemether gave a better survival rate (87.2% vs. 63.3%) and parasite clearance time (54 vs. 78 h) than quinine. Fever clearance times (79 h vs. 84 h) and time to recovery of consciousness (48 h in both groups) were comparable. Previous treatment with quinine or mefloquine had no influence on treatment outcome. The most common adverse effect in patients treated with quinine was tinnitus. Two patients had severe hearing impairment which resolved within 1 week after the end of treatment. Mild, transient pain was noted at the injection site of artemether but no abscess formed. QTc wave prolongation was seen in most patients receiving quinine; however, no arrhythmia was observed despite the high concentration of quinine in some patients who had received quinine before admission. Complications developed in 7 survivors in each treatment group. No patient in the artemether group had neurological sequelae after recovery of consciousness, but 2 in the quinine group had left facial palsy and one had a myasthenia gravis-like syndrome. No patient died with complications in he artemether group, but 7 died with pulmonary complications in the quinine group.

Chemotherapy and prevention of drug-resistant malaria

Drug-resistant falciparum and vivax malaria will continue to be an increasing problem. The incidence of drug-resistant malaria has been increasing at a rate that exceeds new drug development. Plasmodium falciparum has rapidly developed resistance to new synthetic antimalarials, including mefloquine and halofantrine. P. vivax malaria resistant to chloroquine and primaquine is now widespread in parts of Oceania; the optimal therapy for this infection is unknown. At present, a combination of qinghaosu derivatives and mefloquine appears to be the most active drug regimen against multidrug-resistant falciparum malaria from Southeast Asia. However, qinghaosu compounds are not yet licensed and widely available. The capacity of P. falciparum to rapidly develop drug resistance and the growing evidence that other plasmodia can evolve resistance suggests that within the next 10 years, we face the real prospect of untreatable malaria. Ultimately, control of malaria may require more creative approaches than additional inhibitory drugs. These might include: the identification of biochemical pathways unique to the parasite (such as drug efflux and heme polymerase), making it possible to design new classes of antimalarial agents that are selectively toxic to the parasite; methods to block parasite development in the mosquito vector; and multistage vaccines against both asexual and sexual stages in order to block both the pathophysiology and transmission of disease.

Effectiveness of alpha,beta-arteether in acute falciparum malaria

With the emergence of widespread chloroquine resistance and a world-wide scarcity of quinine, a search for newer antimalarial drugs has become imperative. Different derivatives of qinghaosu have been successfully tried. alpha,beta-Arteether, an ethyl derivative of qinghaosu, was administered to 51 patients with Plasmodium falciparum malaria, in a dose of 150 mg intramuscularly once a day on 3 consecutive days. Complete parasite clearance from the peripheral blood was observed in 80% of the patients at 48 h and in 98% at 72 h. The median parasite clearance time was 2 d (range 1-4 d). 65% of the patients became afebrile within 48 h and 81% by 72 h. The mean fever clearance time was 52.04 h (standard deviation 27.09). No side effect was seen. Patients were followed-up for 4 weeks; 7 were readmitted with P. falciparum infection but it could not be ascertained definitely whether these cases were reinfections or recrudescences. alpha-beta Arteether was a safe, effective and convenient drug for treating P. falciparum malaria. This is the first clinical study with arteether in falciparum malaria.

Progress in the research of artemisinin-related antimalarials: an update

Artemisinin, a sesquiterpene lactone endoperoxide isolated from Artemisia annua L., and a number of its semisynthetic derivatives have shown to possess antimalarial properties. They are all effective against Plasmodium parasites that are resistant to the newest and commonly used antimalarial drugs. This article gives a survey of the literature dealing with artemisinin-related antimalarial issues that have appeared from the end of 1989 up to the beginning of 1994. A broad range of medical and pharmaceutical disciplines is covered, including phytochemical aspects like the selection of high-producing plants, analytical procedures, and plant biotechnology. Furthermore, the organic synthesis of artemisinin derivatives is discussed, as well as their mechanism of action and antimalarial activity, metabolism and pharmacokinetics, clinical studies, side-effects and toxicology, and biological activities other than antimalarial activity.

Neurotoxicity of artemisinin analogs in vitro

The sesquiterpene endoperoxide antimalarial agents arteether and artemether have been reported to cause neurotoxicity with a discrete distribution in the brain stems of rats and dogs after multiple doses. The nature and distribution of the brain lesions suggest a specific neuronal target, the identity of which is unknown. In order to further investigate artemisinin analog-induced neurotoxicity, we evaluated several in vitro models: fetal rat primary neuronal cultures, fetal rat secondary astrocyte cultures, and transformed neuronal cultures (rat-derived neuroblastoma NG108-15 and mouse-derived neuroblastoma Neuro-2a). Results indicate that toxicity was specific for neuronal cell types but not glial cells. Neurotoxicity, as indexed by liberation of lactate dehydrogenase and/or inhibition of radiolabelled-leucine uptake, was seen in all three neuronal culture types, implicating a common target. In vitro neurotoxicity was dose and time dependent. Acute exposure to drug results in delayed, but not immediate, manifestations of cell toxicity. Structure-activity comparisons indicate that substitutions at positions 9 and 10 and stereoisomerism at position 10 of the artemisinin backbone influence the degree of toxicity. The endoperoxide is necessary but not sufficient for toxicity. Sodium artesunate and dihydroartemisinin, a metabolite common to all artemisinin analogs currently being developed for clinical use, are the most potent of all analogs tested. These results are consistent with a specific neuronal target, but the identity of the target(s) remains unknown.

Recent advances in tropical medicine

Images

Overview of clinical studies on artemisinin derivatives in Thailand

Over 1000 patients have been treated with artesunate or artemether in clinical trials in Thailand since 1988. These drugs have proved rapidly effective and safe. Combination regimens with mefloquine have proved highly effective against multi-drug resistant Plasmodium falciparum infections. Both drugs are now licensed in Thailand.

Artemisinin: current status

The compounds derived from the Chinese medicinal plant qinghao (Artemisia annua) are the most rapidly acting of all antimalarial drugs. They are effective when given parenterally, orally or by suppository. No serious adverse effect has yet been reported in humans. The artemisinin derivatives already have an established role in the treatment of multi-drug resistant falciparum malaria, but their wider use will depend on the results of current mortality and toxicity studies.

The view of the pharmaceutical industry

Rhône-Poulenc Rorer has committed itself to the development of artemether because we believe the drug will be of considerable benefit to sufferers from severe falciparum malaria, and because it is a stable, effective and economical compound that can be given by intramuscular injection. The quality of the pharmaceutical product meets international regulatory standards. Artemether is unlikely to yield big profits, but we believe that major pharmaceutical companies have a responsibility to develop such much-needed products. To develop this project further, we will need the assistance of academic institutions, research organizations and international bodies.

Parenteral therapy of moderately severe malaria: comparison of intramuscular artemether and intramuscular sulfadoxine-pyrimethamine

We have compared the efficacy of intramuscular artemether against intramuscular sulfadoxine-pyrimethamine in an open randomized study in children with severe but uncomplicated malaria. Parasite clearance time and fever clearance time were faster with artemether. The parasitological clearance on day 14 was 100% for artemether and 98% for sulfadoxine-pyrimethamine, but 8 patients in the artemether group and 1 in the other group had a recrudescence of parasitaemia. There was no toxic reaction of note in either group. We therefore suggest that artemether is a good alternative to the currently used drugs in the parenteral treatment of severe but uncomplicated malaria and may be useful in preventing the possible development of cerebral malaria.

Lactic acidosis and hypoglycaemia in children with severe malaria: pathophysiological and prognostic significance

Serial clinical and metabolic changes were monitored in 115 Gambian children (1.5-12 years old) with severe malaria. Fifty-three children (46%) had cerebral malaria (coma score < or = 2) and 21 (18%) died. Admission geometric mean venous blood lactate concentrations were almost twice as high in fatal cases as in survivors (7.1 mmol/L vs. 3.6 mmol/L; P < 0.001) and were correlated with levels of tumour necrosis factor (r = 0.42, n = 79; P < 0.0001) and interleukin 1-alpha (r = 0.6, n = 34; P < 0.0001). Admission blood venous glucose concentrations were lower in fatal cases than survivors (3.2 mmol/L, vs. 5.8 mmol/L; P < 0.0001). Treatment with quinine was associated with significantly more episodes of post-admission hypoglycaemia when compared with artemether or chloroquine. After treatment, lactate concentrations fell rapidly in survivors but fell only slightly, or rose, in fatal cases. Plasma cytokine levels fluctuated widely after admission. Sustained hyperlactataemia (raised lactate concentrations, 4 h after admission) proved to be the best overall prognostic indicator of outcome in this series. Lactic acidosis is an important cause of death in severe malaria.

The efficacy of artemether in the treatment of Plasmodium falciparum malaria in Sudan

The efficacy of artemether (a qinghaosu derivative) administered intramuscularly for the treatment of Plasmodium falciparum malaria was compared to quinine in an open randomized trial including 54 patients in eastern Sudan, where chloroquine resistance is common. The artemether treatment (5 d intramuscular regimen) was effective and the drug was well tolerated. All patients had cleared the parasitaemia and were free of symptoms 48 h after initiation of treatment. The parasite clearance time was comparable in patients receiving artemether and quinine. No side effect was reported by patients receiving artemether. No recrudescence was seen in 21 patients treated with artemether who completed 28 d follow-up. In the quinine group 3 of 18 patients had recrudescences, or possibly reinfections, on days 14, 21 and 28.

Rapid coma resolution with artemether in Malawian children with cerebral malaria

Artemisinin compounds clear parasitaemia more rapidly than other drugs do in both mild and severe malaria, but no advantage in clinical efficacy has been shown. We have compared artemether treatment with standard quinine treatment in Malawian children with cerebral malaria. 65 unconscious children were randomly allocated to intravenous quinine (n = 37) or intramuscular artemether (n = 28) treatment. The two groups were well matched for various prognostic features. Median parasite clearance times were shorter in the artemether group (28 [interquartile range 18-34] vs 40 [36-44] h in the quinine group, p = 0.0002). Coma resolution times were also shorter with artemether than with quinine (8 [4-15] vs 14 [10-36] h, p = 0.01).

Diagnosis, treatment, and prevention of malaria

Optimal treatment of malaria requires rapid case identification, initiation of specific and supportive therapy based on parasitologic and clinical classification of the patient, and recognition of inadequate response to therapy. Health care providers advising travelers should assess the risk of malaria based on itinerary and clinical condition, and counsel to reduce contact with mosquitoes; prescribe appropriate chemoprophylaxis; and counsel regarding potential side effects and requirement for diagnosis and treatment if fever develops.

An open randomized comparison of intravenous and intramuscular artesunate in severe falciparum malaria

An open paired randomized comparison of intramuscular and intravenous artesunate was conducted in 28 adult patients with severe falciparum malaria. The dose regimen in both groups was 2 mg/kg given immediately followed by 1 mg/kg at 12 and 24 h, and then daily until the patient could swallow. Both routes of administration were well tolerated and there was no evidence of toxicity. One patient in each treatment group died. Clinical and parasitological measures of recovery in survivors were similar in the 2 groups with mean fever clearance times of 37.3 h (standard deviation [SD] = 26.1 h) and 31.5 h (SD = 24.2 h) and mean parasite clearance times of 33.4 h (SD = 13.9 h) and 29.4 h (SD = 12.7 h) in the intravenous and intramuscular groups respectively. Artesunate is equally effective and well tolerated when given by the intravenous or intramuscular routes.