Comparison of oral artemether and mefloquine in acute uncomplicated falciparum malaria

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.

Safety and efficacy of pyronaridine-artesunate in uncomplicated acute malaria: an integrated analysis of individual patient data from six randomized clinical trials

BACKGROUND

Pyronaridine-artesunate (PA) is indicated for the treatment of acute uncomplicated Plasmodium falciparum and Plasmodium vivax malaria.

METHODS

Individual patient data on safety outcomes were integrated from six randomized clinical trials conducted in Africa and Asia in patients with microscopically confirmed P. falciparum (five studies) or P. vivax (one study) malaria. Efficacy against P. falciparum was evaluated across three Phase III clinical trials.

RESULTS

The safety population included 2,815 patients randomized to PA, 1,254 to comparators: mefloquine + artesunate (MQ + AS), artemether-lumefantrine (AL), or chloroquine. All treatments were generally well tolerated. Adverse events occurred in 57.2% (1,611/2,815) of patients with PA versus 51.5% (646/1,254) for comparators, most commonly (PA; comparators): headache (10.6%; 9.9%), cough (5.9%; 5.6%) and anaemia (4.5%; 2.9%). Serious averse events were uncommon for all treatments (0-0.7%). Transient increases in alanine aminotransferase and aspartate aminotransferase were observed with PA but did not lead to any clinical sequelae. For P. falciparum malaria, day-28 PCR-corrected adequate clinical and parasitological response with PA was 93.6% ([1,921/2,052] 95% CI 92.6, 94.7) in the intent-to-treat population and 98.5% ([1,852/1,880] 95% CI 98.0, 99.1) in the per-protocol population. Median parasite clearance time was 24.1 h with PA, 31.9 h with MQ + AS, and 24.0 h with AL. Median fever clearance time was 15.5 h with PA, 15.8 h with MQ + AS, and 14.0 h with AL. By day 42, P. falciparum gametocytes had declined to near zero for all treatments.

CONCLUSIONS

Pyronaridine-artesunate was well tolerated with no safety concerns with the exception of mostly mild transient rises in transaminases. Efficacy was high and met the requirements for use as first-line therapy. Pyronaridine-artesunate should be considered for inclusion in malaria treatment programmes.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT00331136; NCT00403260; NCT00422084; NCT00440999; NCT00541385; NCT01594931.

Elimination therapy for the endemic malarias

Most malaria diagnosed outside endemic zones occurs in patients experiencing the consequences of what was likely a single infectious bite by an anopheline mosquito. A single species of parasite is nearly always involved and expert opinion on malaria chemotherapy uniformly prescribes species- and stage-specific treatments. However the vast majority of people experiencing malaria, those resident in endemic zones, do so repeatedly and very often with the involvement of two or more species and stages of parasite. Silent forms of these infections-asymptomatic and beyond the reach of diagnostics-may accumulate to form substantial and unchallenged reservoirs of infection. In such settings treating only the species and stage of malaria revealed by diagnosis and not others may not be sensible or appropriate. Developing therapeutic strategies that address all species and stages independently of diagnostic evidence may substantially improve the effectiveness of the control and elimination of endemic malaria.

Plasmodium vivax recurrence following falciparum and mixed species malaria: risk factors and effect of antimalarial kinetics

BACKGROUND

Plasmodium vivax malaria commonly follows treatment of falciparum malaria in regions of co-endemicity. This is an important cause of preventable morbidity.

METHODS

We examined the factors contributing to the risk of recurrence of P. vivax infection after treatment of acute falciparum malaria in a series of clinical trials conducted on the Thai-Myanmar border from 1991 through 2005.

RESULTS

Overall, 10,549 patients (4960 children aged <15 years and 5589 adults) were treated for falciparum malaria; of these patients, 9385 (89.0%) had Plasmodium falciparum monoinfection and 1164 (11.0%) had mixed P. falciparum/P. vivax infections according to microscopic examinations performed at screening. The cumulative proportion of patients with P. falciparum infection recurrence by day 63 was 21.5% (95% confidence interval [CI], 20.3%-22.8%), and the cumulative proportion with P. vivax infection recurrence was 31.5% (95% CI, 30.1%-33.0%). Significant risk factors for P. vivax infection recurrence were mixed infection at enrollment, male sex, younger age, lower hematocrit, higher asexual P. falciparum parasite density (P < .001 for all factors), and P. falciparum gametocytemia at enrollment (P = .001). By day 63, the cumulative risk of vivax malaria after P. falciparum monoinfection was 51.1% (95% CI, 46.1%-56.2%) after treatment with rapidly eliminated drugs (t(1/2) <1 day), 35.3% (95% CI, 31.8%-39.0%) after treatment with intermediate half-life drugs (t(1/2) 1-7 days), and 19.6% (95% CI, 18.1%-21.3%) after treatment with slowly eliminated drugs (t(1/2) > 7 days) (P < .001, by test for trend). Artemisinin-based combinations containing mefloquine or piperaquine, compared with the artemether-lumefantrine and artesunate-atovaquone-proguanil combinations, were associated with a 3.6-fold to 4.2-fold lower adjusted hazard ratio for P. vivax infection recurrence within 63 days after pure or mixed P. falciparum infections (P < .001, for comparisons with artesunate-mefloquine).

CONCLUSIONS

On the Thai-Myanmar border, P. vivax is the most common cause of parasitological failure after treatment for falciparum malaria. Slowly eliminated antimalarials reduce the risk of early P. vivax infection recurrence.

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.

Stability of artesunate in pharmaceutical solvents

Stability of artesunate (ART) was established in three pharmaceutical solvents. The chromatographic conditions developed for this study were acetonitrile:potassium phosphate buffer 10 mM (40:60, v:v; pH 2.9) at 0.7 mL min(-1) with UV detection at 220 nm using a short X-Terra RP C18 column (50 mm x 3 mm, 3.5 microm). This isocratic condition led to the separation between ART and its main degradation products (i.e. alpha-DHA and beta-DHA) with analysis time of less than 4 min. The retention factors are 1.49, 2.26 and 2.79 min for alpha-DHA, beta-DHA and ART, respectively. This method was proved linear (r(2)=0.9995), accurate (R.S.D.=0.20), precise (R.S.D.=0.74) and robust. The system performance remained unaffected by pH variation from 2.6 to 3.2 and variation of acetonitrile percentage from 38 to 42. Stability of ART was assessed in ethanol, propylene glycol (PG) and polyethylene glycol 400 (PEG 400). Unfortunately none of these solvents prevented ART from degradation longer than 3 months. In ethanol, significant degradation of ART occurred after 3 months at room temperature and this degradation was characterised by numerous degradation products. In PEG 400, significant degradation was observed after only 1 month, however DHA was the unique degradation product, which is also an efficient anti-malarial drug.

Clinical-parasitological response and in-vitro sensitivity of Plasmodium vivax to chloroquine and quinine on the western border of Thailand

This study was conducted during 2002-2004 at Mae Sot District, on the Thai-Myanmar border, an area of multidrug-resistant Plasmodium falciparum malaria. Sixty-two patients with P. vivax malaria were included in the study. All were randomized into two groups to receive a 3-day regimen of chloroquine or a 3-day regimen of quinine. Primaquine was given to patients in both groups for the elimination of hepatic stages. Results from the present study suggest that the standard regimen of chloroquine and a 3-day course of quinine at the dose regimens under investigation were very effective and well tolerated for the treatment of P. vivax malaria in this area. All patients responded well to both drug regimens; the cure rates with chloroquine or quinine, when given concurrently with the tissue schizontocidal drug primaquine, were virtually 100% within 28 days of follow-up. No significant correlations between parasite clearance time (PCT) or fever clearance time (FCT) and inhibitory concentration 50 (IC50) were found. Patients who had PCT < or = 24 h and those with PCT >24 h had comparable IC50 to chloroquine (alone and plus primaquine) and quinine, as well as similar concentrations of chloroquine/desethylchloroquine (in blood) or quinine (in plasma) at the investigated time points.

Effects of Artemisinin, Artemether, Arteether on the Pharmacokinetics of Carbamazepine

The effect of artemisinin, artemether and arteether on the pharmacokinetics of carbamazepine in rabbits was studied. In a cross-over study, carbamazepine 40 mg/kg/day orally was given daily for 7 days. On day 7, blood samples were taken at various time intervals between 0 and 24 h. In the artemisinin group, carbamazepine was administered for 7 days as above. On day 8, artemisinin 82 mg/kg followed by 41 mg/kg on the 9th and 10th day along with carbamazepine 40 mg/kg/day was administered and blood samples drawn as above. Artemether 10 mg/kg i.m. was given on day 8 followed by 5 mg/kg i.m. for 2 days. Arteether 10 mg/kg i.m. was given from day 8 for 3 days. Plasma carbamazepine levels were assayed by high-performance liquid chromatography and pharmacokinetic parameters calculated. In all the groups there was an increase in the AUC(0-infinity) when carbamazepine was co-administered with artemisinin, artemether or arteether. The increase in AUC(0-infinity) (22.78 +/- 4.71 to 63.10 +/- 12.29), Cmax (2.76 +/- 0.77 to 7.02 +/- 1.08), Tmax (2.83 +/- 0.17 to 4.16 +/- 0.40) was statistically significant when artemether was given along with carbamazepine (p < 0.05). In the other groups the increase was not significant. These results suggest artemisinin compounds alter the pharmacokinetics of carbamazepine with significant change in the bioavailability. Confirmation of these results in human studies will warrant changes in carbamazepine dose or frequency when either of these antimalarials is co-administered with it.

Mefloquine resistance in Plasmodium falciparum

Mefloquine resistance in Plasmodium falciparum, the most dangerous of the four pathogenic malaria parasites of humans, is established in several endemic regions of the world. After a promising start, resistance has developed to disturbing extents in some areas, whereas in many regions it remains an effective drug. In this article, Frank Mockenhaupt reviews the factors that are likely to influence the development of mefloquine resistance, its possible mechanism and its geographical spread.

Therapeutic responses to antimalarial and antibacterial drugs in vivax malaria

Plasmodium vivax is the most prevalent malaria infection and is an important cause of morbidity in Central and South America and Asia. P. vivax is generally sensitive to the common antimalarial drugs but high level resistance to chloroquine and/or pyrimethamine has been documented in some geographic locations. In the studies reviewed here, the therapeutic responses to antimalarial and antibacterial drugs in vivax malaria have been assessed in the Bangkok Hospital for Tropical Diseases. The evaluated drugs consisted of the eight most widely used antimalarial drugs and anti-bacterial drugs that possess antimalarial activities (tetracycline, doxycycline, clindamycin or azithromycin). The activities of these drugs in descending order of parasite clearance times were artesunate, artemether, chloroquine, mefloquine, quinine, halofantrine, primaquine, followed by the antibacterial drugs and lastly sulfadoxine-pyrimethamine. Clinical responses to sulfadoxine-pyrimethamine were also poor with evidence of high grade resistance in 42% of the patients. Of the four antibacterial drugs, clindamycin was more effective than azithromycin and can be an alternative to the tetracyclines. Except for chloroquine and mefloquine which have long plasma half lives and may therefore suppress first relapses, the cumulative cure rates for the short acting antimalarial drugs were similar. Double infection with Plasmodium falciparum was common and usually manifested 3-4 weeks following clearance of vivax malaria. The prevalence of cryptic falciparum malaria was 8-15% and was higher in patients treated with less potent antimalarial drugs. Follow-up studies have revealed that the relapse time in Thai patients with vivax malaria is on average only 3 weeks, but can be suppressed by the slowly eliminated antimalarial drugs such as chloroquine and mefloquine. For accurate comparison of relapse/recrudescence rates in vivax malaria, at least 2 month's follow-up is required. It can be concluded that in malarious areas of Thailand, double infection with P. falciparum and P. vivax is common affecting at least 25% of the patients and usually manifests as sequential illnesses. P. vivax in Thailand is sensitive to chloroquine but has acquired high grade resistance to sulfadoxine-pyrimethamine.

Dose-finding and efficacy study for i.m. artemotil (beta-arteether) and comparison with i.m. artemether in acute uncomplicated P. falciparum malaria

AIMS

The antimalarial efficacy/pharmacodynamics and pharmacokinetics of intramuscular (i.m.) artemotil in Thai patients with acute uncomplicated falciparum malaria were studied to determine effective dose regimens and to compare these with the standard dose regimen of artemether.

METHODS

In part I of the study three different artemotil dose regimens were explored in three groups of 6-9 patients for dose finding: 3.2 mg kg-1 on day 0 and 1.6 mg kg-1 on days 1-4 (treatment A), 1.6 mg kg-1 on day 0 and 0.8 mg kg-1 on days 1-4 (treatment B), 3.2 mg kg-1 on day 0 and 0.8 mg kg-1 on days 1-4 (treatment C). In part II of the study, artemotil treatments A and C were compared in three groups of 20-22 patients with standard i.m. artemether treatment: 3.2 mg kg-1 on day 0 and 0.8 mg kg-1 on days 1-4 (treatment R).

RESULTS

Full parasite clearance was achieved in all patients in Part I, but parasite clearance time (PCT) and fever clearance time (FCT) tended to be longer in treatment B. Also the incidence of recrudescence before day 28 (RI) tended to be higher for treatment B. In part II, the mean PCT for each of the two artemotil treatments (52 and 55 h, respectively) was significantly longer than for artemether (43 h). The 95% CI for the difference A vs R was 0, 16 h (P=0.0408) and for difference C vs R it was 2, 19 h (P=0.0140). FCT was similar for the three treatments. The incidence of RI ranged from 5 out of 19 for treatment C to 3 out of 20 for treatment R. Plasma concentration-time profiles of artemotil indicated an irregular and variable rate of absorption after i.m. injection. A late onset of parasite clearance was associated with delayed absorption and/or very low initial artemotil plasma concentrations. Pharmacokinetic-pharmacodynamic evaluations supported a relationship between the rate of parasite clearance and exposure to artemotil during approximately the first 2 days of treatment, and suggested that artemotil has a slower rate of absorption than artemether. Safety assessment, including neurological and audiometric examinations showed no clinically relevant findings. Adverse events before and during treatment included headache, dizziness, nausea, vomiting and abdominal pain. These are characteristic of acute malaria infections and resolved during treatment.

CONCLUSIONS

The optimum dose regimen for artemotil in this study was identical to the standard dose regimen of artemether. The findings that artemotil is more slowly absorbed from the i.m. injection site than artemether, and that early systemic availability may be insufficient for an immediate onset of parasite clearance contributed to the decision to choose a higher loading dose of artemotil (divided over two injection sites) and to omit the fifth dose in later studies. With this optimized dosing schedule, the more pronounced depot characteristics of i.m. artemotil can be an advantage, since it may allow shorter hospitalization.

Artemisinin pharmacokinetics and efficacy in uncomplicated-malaria patients treated with two different dosage regimens

The immediate efficacies of two oral dosage regimens of artemisinin were investigated in 77 male and female adult Vietnamese falciparum malaria patients randomly assigned to treatment with either 500 mg of artemisinin daily for 5 days (group A; n = 40) or artemisinin at a dose of 100 mg per day for 2 days, with the dose increased to 250 mg per day for 2 consecutive days and with a final dose of 500 mg on the fifth day (group B; n = 37). Parasitemia was monitored every 4 h. The average parasite clearance time was longer in group B than in group A (means +/- standard deviations, 50 +/- 23 and 34 +/- 14 h, respectively; P < 0.01). Artemisinin concentrations in saliva samples obtained on days 1 and 5 were quantified by high-performance liquid chromatography. The average oral clearance, based on saliva drug concentrations in group B patients, was twofold higher than that in group A patients on day 1 (P < 0.01), with no differences in drug half-lives (P = 0.40), indicating a saturable first-pass metabolism. Female patients had higher oral clearance values on day 1. Artemisinin's pharmacokinetic parameters were similar on day 5 in both groups, although a significant increase in oral clearance from day 1 to day 5 was evident. Thus, artemisinin exhibited both dose- and time-dependent pharmacokinetics. The escalating dose studied did not result in higher artemisinin concentrations toward the end of the treatment period.

Therapeutic responses to antibacterial drugs in vivax malaria

Some antibacterial drugs have antimalarial activity that can be exploited for the prevention or treatment of malaria. Monotherapy with tetracycline, doxycycline, clindamycin or azithromycin was assessed in 1995-98 in 92 adult patients in Thailand with Plasmodium vivax malaria. All patients recovered following treatment and the early therapeutic responses were similar among the 4 groups. The overall median fever clearance time was 57 h and the mean (SD) overall time to parasite clearance was 134 (48) h. Of 66 patients who completed a 28-day follow-up, reappearances of vivax infection occurred in 27 patients (41%) from all groups; delayed appearances of falciparum malaria occurred in 6 patients (9%), only from the azithromycin group. The overall mean (SD) time to reappearance of P. vivax was 23 (5) days and time taken for detection of falciparum malaria was 13 (4) days after starting treatment for vivax malaria. The 28-day cumulative cure rates of clindamycin (n = 12), tetracycline (n = 18) and doxycycline (n = 18) groups were similar (P > or = 0.14) and all were significantly higher compared to the azithromycin group (n = 18; P < or = 0.04). The intervals until vivax reappearance were also significantly shorter in the azithromycin group [mean (SD) = 21 (6) vs 25 (3) days, P < 0.05] suggesting that some of these were recrudescences. The apparent success rate (no subsequent appearances of either vivax or falciparum infection) was significantly lower for the azithromycin group (11%) compared to the other groups (34-78%; P < 0.01). In current antibacterial treatment regimens, short-course azithromycin has inferior antimalarial activity compared to clindamycin or the tetracyclines.

In vitro sensitivity of Plasmodium falciparum and clinical response to lumefantrine (benflumetol) and artemether

AIMS

To assess the sensitivity of 103 Plasmodium falciparum isolates to a combination of lumefantrine (benflumetol) and artemether (CGP 56697), with the objective of determining a correlation between in vitro drug sensitivity and therapeutic outcome.

METHODS

Patients suffered from uncomplicated falciparum malaria and came from areas of Thailand affected by multidrug resistance. CGP 56697 was given in the form of tablets containing 20 mg artemether and 120 mg lumefantrine. The standard dose regimen, 4 doses of 4 tablets over 48 h, was compared with two lower dose regimens (4 x 2 tablets and 3 x 4 tablets).

RESULTS

The parasites showed high resistance to chloroquine, fairly advanced resistance to mefloquine and compromised sensitivity to quinine. Sensitivity to artemisinin and lumefantrine prior to treatment was similar in all treatment groups. The 4 x 4 tablet regimen was more effective than the other regimens in coping with infections with relatively low sensitivity to artemisinin and/or lumefantrine. The EC90 for artemisinin is an important determinant of treatment success. Parasite density at the start of treatment was identified as another critical predictor of treatment outcome.

CONCLUSIONS

The results indicate that parasite exposure to the drugs may have been inadequate and/or too short in the cases of treatment failure, particularly marked in the lower dose regimens. This could probably be remedied by expanding the dose regimen in areas affected by multidrug resistance and in the case of relatively high parasitaemia.

The prophylactic effects of artemether against Schistosoma japonicum infections

The fight against schistosomiasis in China has been very effective in reducing the number of infections across the country. However, the drug of choice, praziquantel, has no prophylactic effect, which reduces its efficacy in high transmission areas. This situation has prompted efforts to find prophylactic compounds, the most promising of which is the drug artemether. In this article, Xiao Shuhua, Mark Booth and Marcel Tanner review the results of laboratory tests and field trials of artemether against schistosomiasis in China.

Artemisinin derivatives for treating uncomplicated malaria

BACKGROUND

Artemisinin derivatives are a relatively new group of drugs with antimalarial properties. As resistance to other antimalarial drugs continues to increase, artemisinin drugs may be useful alternatives.

OBJECTIVES

The objective of this review was to assess the effects of artemisinin drugs for treating uncomplicated falciparum malaria.

SEARCH STRATEGY

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

SELECTION CRITERIA

Randomised and quasi-randomised trials of artemisinin derivatives, alone or in combination with other antimalarials, compared with standard antimalarial treatments, in adults or children with uncomplicated falciparum malaria. Only trials where treatment was given by mouth or suppository were included. Comparisons between different artemisinin derivatives and treatment regimens were also included.

DATA COLLECTION AND ANALYSIS

Eligibility and trial quality were assessed and data were extracted independently by the two reviewers.

MAIN RESULTS

Forty-one trials involving over 5000 patients were included. Variation in study design and quality made synthesis of the data problematic. Allocation concealment was adequate in only two trials. Most data were from areas of multidrug resistant falciparum malaria in South East Asia. Compared with standard antimalarial treatments, artemisinin drugs showed fast parasite clearance and high cure rates at follow-up, provided the duration of treatment with artemisinin drugs was adequate. Combination with mefloquine improved sustained parasite clearance and was effective in multidrug resistant areas. When doses were adequate, the combination shortened the duration of treatment. We found no evidence that artemisinin drugs are more harmful than standard treatment drugs over a typical trial period of 28 days.

REVIEWER'S CONCLUSIONS

The evidence suggests that artemisinin drugs are effective and safe for treating uncomplicated malaria. There is no evidence from randomised trials that one artemisinin derivative is better than the others. In areas where there is mefloquine resistance, combination therapy with an artemisinin derivative appears to improve sustained parasite clearance compared with either drug alone.

Population pharmacokinetics and therapeutic response of CGP 56697 (artemether + benflumetol) in malaria patients

AIMS

To investigate the pharmacokinetic and pharmacodynamic properties of artemether and benflumetol in a fixed combination tablet (CGP 56697) and to offer an explanation for the lower than expected cure rate in a Thai clinical trial.

METHODS

Two hundred and sixty patients were enrolled into a randomized, double-blind, parallel group, dose-finding trial. CGP 56697 was given orally, either as: A, 4 x 4 tablets over 48 h; B, 4 x 2 tablets over 48 h or C, 3 x 4 tablets over 24 h. Each tablet contained artemether 20 mg amd benflumetol 120 mg. The pharmacokinetics were determined using a population-based approach combining full profiles (42 patients) and sparse data (218 patients). Parasite clearance time and 28 day cure rate were correlated with the derived pharmacokinetic parameters.

RESULTS

The median absorption half-life of benflumetol was 5.3 h, with a tmax of 10 h and terminal elimination half-life of 4.5 days. For artemether (and its metabolite, dihydroartemisinin), the corresponding values were 1.9 (1.9) h, 1.8 (1.2) h, and 0.84 (0.43) h. The variability in bioavailability of artemether and dihydroartemisinin was large both between doses and between patients, but was less pronounced for benflumetol. Compared with the first dose, benflumetol bioavailability was estimated to increase three-fold by the third and fourth doses. Higher artemether or dihydroartemisinin AUC was found to decrease parasite clearance time. Higher benflumetol AUC was found to significantly increase the chance of cure.

CONCLUSIONS

Using a population-based approach it was confirmed that the pharmacokinetic and pharmacodynamic properties of benflumetol and artemether differ markedly. Benflumetol AUC is associated with cure and the effect of benflumetol when coadministered with artemether is to prevent recrudescence. The mode of action of benflumetol is consistent with its longer elimination half-life. A short course of low-dose artemether, which is rapidly absorbed and has a short elimination half-life, produced effective parasite clearance. The complementary pharmacokinetic and pharmacodynamic properties of benflumetol and artemether was the main rationale for developing a fixed-dose combination. While the 4 x 4 dose regimen is very effective in most endemic areas, the poorer absorption (2.5 fold lower than in China) and the more resistant parasites in Thailand require higher doses of this drug.

Pharmacokinetics of intramuscular artemether in patients with severe falciparum malaria with or without acute renal failure

AIMS

The pharmacokinetics of intramuscular artemether and its major plasma metabolite-dihydroartemisinin, were investigated in patients with severe manifestations of falciparum malaria.

METHODS

Six severe falciparum malaria patients with acute renal failure (ARF) and 11 without ARF were recruited into the study. They were treated with intramuscular artemether at a loading dose of 160 mg, followed by daily doses of 80 mg for another 6 days (total dose 640 mg).

RESULTS

Patients with and without ARF showed a good initial response to treatment; the parasite and fever clearance times were 66(30-164) and 76(36-140) h [median(range)], respectively. None had reappearance of parasitaemia in their peripheral blood smear within 7 days of initiation of treatment. In comatose patients, the time to recovery of consciousness was 51.6(22-144) h. Artemether was detected in plasma as early as 1 h after a 160 mg dose, and declined to undetectable levels within 24 h in most cases. Patients with ARF had significantly higher Cmax [2.38(1.89-3.95) vs 1.56(1.05-3.38) ng ml(-1) mg(-1) dose], AUC [35.4(22-52.9) vs 25.2(13.4-52.9) ng ml(-1) h mg(-1) dose], and lower Vz/F [5.45(3.2-6.9) vs 8.6(4.2-12.3) l kg(-1)] and CL/F [7.4(5.4-13.8) vs 19.1(8.5-25.1) ml min(-1) kg(-1)] when compared with those without ARF. In addition, t1/2,z was significantly longer in ARF patients [7.0(5.5-10.0) vs 5.7(4.2-6.6) h]. The pharmacokinetics of dihydroartemisinin in the two groups of patients were comparable.

CONCLUSIONS

ARF significantly modified the pharmacokinetics of intramuscular artemether. The changes could be attributed to either improved absorption/bioavailability, a reduction of systemic clearance, or a change in plasma protein binding of the drug.

Simple high-performance liquid chromatographic method with electrochemical detection for the simultaneous determination of artesunate and dihydroartemisinin in biological fluids

A simple, rapid, sensitive, selective and reproducible high-performance liquid chromatographic method with reductive electrochemical detection is described for the simultaneous quantification of artesunate (ARS) and dihydroartemisinin (DHA) in plasma. The procedure involved the extraction of ARS, DHA and the internal standard (artemisinin, ARN) with a mixture of dichloromethane and tert.-methyl butyl ether (8:2, v/v). Chromatographic separation consisted of the mobile phase (acetonitrile-water containing 0.1 M acetic acid, pH 4.8; 45:55, v/v) running through the column (Nova-Pak C18, 150 cm x 3.9 mm I.D., 5 microm particle size). The retention times of alpha-DHA, beta-DHA, ARS and ARN were 2.9, 4.2, 4.5 and 6.0 min, respectively. The average recoveries of ARS, alpha-DHA and ARN in the concentration range of 10-800 ng/ml were 81.9, 88.2, 101.1 and 84.3%, respectively. The coefficients of variation (precision and repeatability) were below 10% for all three compounds at concentrations of 50, 200, 400 and 800 ng/ml, and below 20% at a concentration of 10 ng/ml. The limits of quantification for both ARS and alpha-DHA in spiked plasma samples were 5 and 3 ng/ml, respectively. The method was found to be suitable for application to pharmacokinetic studies of both ARS and DHA.

Avaliação da eficácia do artesunato associado à tetraciclina na terapêutica da malária falciparum

Realizou-se um ensaio clínico, randomizado e controlado, comparando o artesunato com o quinino e a mefloquina, em casos de malária não grave. Foram tratados 42 pacientes em regime de internação e o seguimento durou 28 dias. Realizou-se exame de gota espessa cada 12 horas até sua negativação, hemograma e bioquímica sanguínea, pré e pós-tratamento. A média da parasitemia inicial foi 42.568 parasitas/ml. Vinte e seis pacientes foram acompanhados durante 28 dias e 16 durante menos de 28 dias. Um paciente de cada grupo apresentou R I tardia e um paciente do grupo do quinino apresentou R III. As porcentagens de cura foram 88,8%, 85,7% e 81,8% para o artesunato, a mefloquina e o quinino, respectivamente, sem mostrar diferença significativa. O tempo de desaparecimento da febre não mostrou diferença significativa entre os grupos. O grupo do artesunato teve um tempo menor de clareamento da parasitemia (37,33 ± 11,52 horas) quando comparado com o quinino (65,25 ± 17,44 horas), sendo estatisticamente significativa (p = 0,0016). O grupo da mefloquina (58,9 ± 16,68 horas) não mostrou diferença com os outros grupos. Não se apresentaram efeitos adversos importantes em nenhum dos esquemas usados, sendo bem tolerados pelos pacientes.

Determination of artemether and its major metabolite, dihydroartemisinin, in plasma using high-performance liquid chromatography with electrochemical detection

A rapid, selective, sensitive and reproducible HPLC with reductive electrochemical detection for quantitative determination of artemether (ART) and its plasma metabolite, dihydroartemisinin (DHA: alpha and beta isomers) in plasma is described. The procedure involved the extraction of ART, DHA and the internal standard, artemisinin (ARN) with dichloromethane-tert.-methylbutyl ether (1:1, v/v) or n-butyl chloride-ethyl acetate (9:1, v/v). Chromatographic separation was performed with a mobile phase of acetonitrile-water (20:80, v/v) containing 0.1 M acetic acid pH 5.0, running through a microBondapak CN column. The method was capable of separating the two isomeric forms of DHA (alpha, beta). The retention times of alpha-DHA, beta-DHA, ARN and ART were 4.6, 5.9, 7.9 and 9.6 min, respectively. Validation of the assay method was performed using both extraction systems. The two extraction systems produced comparable recoveries of the various analytes. The average recoveries of ART, DHA and ARN over the concentration range 80-640 ng/ml were 86-93%. The coefficients of variation were below 10% for all three drugs (ART, alpha-DHA, ARN). The minimum detectable concentrations for ART and alpha-DHA in spiked plasma samples were 5 and 3 ng/ml, respectively. The method was found to be suitable for use in clinical pharmacokinetic study.

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.

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.

Pharmacokinetics of mefloquine, when given alone and in combination with artemether, in patients with uncomplicated falciparum malaria

The pharmacokinetics of mefloquine at a single oral dose of 750 mg, when given alone or 24 hours after a single oral dose of artemether (300 mg) was investigated in 27 Thai patients with acute uncomplicated falciparum malaria (17 with mefloquine alone, 10 with the combination). The oral bioavailabiiity of mefloquine was significantly decreased when administered 24 hours after an oral dose of artemether. This was evident by the significantly lower values of Cmax, AUC[0-24 h], AUC[0-48 h], AUC[0-72 h], as well as total AUC[Cmax: 1,290 (827-2,619) vs 1,820 (1,283-2,531) ng.ml-1; AUC[0-24 h]: 0.99 (0.64-1.41) vs 1.33 (1.07-1.95) micrograms.day.ml-1; AUC[0-48 h]: 1.78(1.23-2.58) vs 2.67 (2.09-3.84) micrograms.day.ml-1; AUC[0-72 h]: 2.74 (1.63-3.6) vs 4.54 (2.88-5.38) micrograms.day.ml-1; AUC: 11.11 (6-20.96) vs 15.29 (9.3-36.71) micrograms.day.ml-1]. Tmax was also delayed with the combination regimen [14 (5-24) vs 6 (4-16) h]. Terminal elimination half-lives were comparable [t1/2z: 11.1 (6.8-14.3) vs 13.4 (10.5-19.1) h].

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.

Artesunate versus artemether in combination with mefloquine for the treatment of multidrug-resistant falciparum malaria

To compare the therapeutic efficacy of oral artesunate and artemether in combination with mefloquine for the treatment of multidrug resistant malaria, a trial was conducted in 540 adults and children on the Thai-Myanmar border. Three regimens were compared: artesunate (4 mg/kg/d for 3 d), artemether (4 mg/kg/d for 3 d), both in combination with mefloquine (25 mg/kg), and a single dose of mefloquine (25 mg/kg). The artesunate and artemether regimens gave very similar clinical and parasitological responses, and were both very well tolerated. There was no significant adverse effect attributable to the artemisinin derivatives. Fever and parasite clearance times with mefloquine alone were significantly longer (P < 0.001). After adjusting for reinfections the failure rates were 13.9% for the artesunate combination, 12.3% for the artemether combination and 49.2% for mefloquine alone (P < 0.0001; relative risk 3.8 [95% confidence interval 2.6-5.4]). Mefloquine should no longer be used alone for the treatment of multidrug resistant falciparum malaria in this area. Three-day combination regimens with artesunate or artemether are well tolerated and more effective.

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.

A comparative clinical trial of two different regimens of artemether plus mefloquine in multidrug resistant falciparum malaria

Plasmodium falciparum in Thailand is highly resistant to available antimalarial drugs. Artemether, a derivative of artemisinin, is a promising compound currently used to cope with this situation but the course of treatment has to be at least 5 d. An effective short treatment course of this drug is possible when used in combination with mefloquine. We now report a trial of different regimens of the combination artemether/mefloquine. Fifty-seven male Thai patients, admitted to the Bangkok Hospital for Tropical Diseases, were allocated at random to receive oral artemether 300 mg as an initial dose, followed by either the standard dose of mefloquine (750 mg) at 24 h or a higher dose of mefloquine (750 mg at 24 h, then 500 mg at 30 h). Patients were followed up in hospital for 42 d. Two patients, both in the high dose mefloquine group, were excluded as they failed to attend for follow-up. All patients had a rapid initial response to treatment with median parasite clearance times of 37 and 40 h, median fever clearance times of 33.5 and 30.5 h, and cure rates of 75 and 96% (P = 0.0248), for the standard and high doses of mefloquine respectively. No serious adverse effect was found; mild and transient dizziness, nausea, vomiting and diarrhoea were noted in half of the patients in each group. The results suggest that a 30 h short course of artemether plus mefloquine at high dose should be used in areas with documented mefloquine resistance.

Single dose artemisinin-mefloquine treatment for acute uncomplicated falciparum malaria

For the treatment of patients with acute falciparum malaria, the combination of artemisinin as a single dose with a single dose of mefloquine was studied in 4 separate prospective trials, comprising 405 adults and 139 children with uncomplicated falciparum malaria in 2 in-patient and 2 rural out-patient studies in Viet Nam. Adults received oral artemisinin and children artemisinin suppositories. Randomized comparative treatment schedules were: artemisinin alone for 5 d, mefloquine-sulfadoxine-pyrimethamine (MSP), or quinine plus sulfadoxine-pyrimethamine (SP). Parasite clearance times (PCT) were rapid for artemisinin treated inpatients (90%: 14.8-20.4 h) but also for patients receiving MSP (PCT 90%: 18.0 h) and quinine (PCT 90%: 22.5 h). The recrudescence rate (RI) during a 28 d follow-up period among the patients given artemisinin plus mefloquine was 15% in the adult in-patients and zero in the adult and children out-patients. RI in the artemisinin 5 d treatment group was 33.3%; among those given artemisinin plus SP it was 47.3% in in-patients and in out-patients 46.1%. In the MSP treated out-patients RI was 1.5% in adults and zero in children. Artemisinin as a single dose (oral in adults and as a suppository in children) in combination with mefloquine was effective in rapidly lowering parasitaemia and in preventing recrudescence in hospital in-patients and in out-patients attending a rural health clinic. MSP alone as a single dose also rapidly reduced parasitaemia (but not as quickly as the artemisinin-mefloquine combination in out-patient children) and prevented recrudescence.

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.

Pharmacokinetics of artemether after oral administration to healthy Thai males and patients with acute, uncomplicated falciparum malaria

1. The pharmacokinetics of artemether were investigated (a) in six healthy male Thai volunteers after single 200 mg oral doses and (b) in eight male Thai patients with acute uncomplicated falciparum malaria after an initial 200 mg oral dose followed by 100 mg at 12 h then 100 mg daily for 4 days. 2. In the healthy subjects, median (range) maximum plasma concentrations of artemether of 118 (112-127) ng ml-1 were reached at 3 (1-10) h. Thereafter, drug concentrations declined monoexponentially with a median (range) t1/2.z of 3.1 (1.0-9.6) h. The median (range) AUC and MRT values were 1.10 (0.33-4.44) micrograms ml-1 h and 8.3 (3.5-20.8) h. The median Cmax value of dihydroartemisinin, an active metabolite, was 379 (162-702) mg ml-1 at 6 (2-12) h. Its median AUC value was 6.6 (0.83-38.7) micrograms ml-1 h; the apparent t1/2.z was 10.6 (4.7-19.2) h and the median MRT value was 16.0 (5.0-41.0) h. 3. In the patients, a higher Cmax value of parent drug than those observed in healthy subjects (median and range of 231 (116-411) ng ml-1), was reached at 3 (1-3) h after the first dose. Steady state was reached after the third dose (24 h) and concentrations fluctuated over the range of 36-60 ng ml-1. The respective median (range) values of AUC and t1/2.z were 5.8 (3.76-12.9) micrograms ml-1 h and 4.2 (2.5-5.3) h.(ABSTRACT TRUNCATED AT 250 WORDS)

Mefloquine. A review of its antimalarial activity, pharmacokinetic properties and therapeutic efficacy

Mefloquine is an orally administered blood schizontocide. Initial dose-finding and comparative studies performed between 1977 and 1989 demonstrated efficacy of mefloquine as prophylaxis in nonimmune individuals and in the suppression and treatment of malaria in adults and children caused by multidrug-resistant Plasmodium falciparum. It was also effective against P. vivax infection, while data concerning the treatment of P. ovale and P. malariae infections were limited. In an attempt to delay the emergence of resistance to this promising antimalarial agent, mefloquine was combined with sulfadoxine and pyrimethamine. Although initial clinical trials indicated that this regimen was effective in preventing and treating falciparum malaria, recent treatment failures, the potential for severe dermatological reactions and lack of therapeutic advantage over mefloquine alone has prompted the World Health Organization to recommended that the combination be no longer used for treatment or prophylaxis of malaria. Mefloquine is generally well tolerated in both adults and children, with nausea, vomiting, diarrhoea, headache, dizziness, rash, pruritus and abdominal pain being the most common adverse effects, although it is difficult to distinguish between disease- and treatment-related events. The incidence of these adverse effects is similar to or lower than those observed with other antimalarial agents. Cardiovascular changes, such as bradycardia, occasionally occur. The most notable adverse effects associated with mefloquine are neuropsychiatric disturbances; precipitation of such events should be closely monitored and requires termination of prophylaxis or therapy. The eventual emergence of resistance to mefloquine, as with many other antimalarial agents, was inevitable. Mefloquine resistance is established in certain areas of Thailand and may be becoming a growing problem in other regions of the world. In order to preserve the efficacy of mefloquine in non-resistant areas, this useful agent should be used with care and only prescribed for prophylaxis in travellers and treatment in areas of multidrug-resistant plasmodia. Future options to combat mefloquine resistance may include the combination of mefloquine with other antimalarial agents such as qinghaosu derivatives. Thus, with cautious use and possible combination with other agents, mefloquine is likely to remain an important treatment option for falciparum malaria, a widespread parasitic disease for which an increasing number of drugs have proved inadequate.