Multiple dose pharmacokinetics of artemether in Chinese patients with uncomplicated falciparum malaria

The Impact of Extended Treatment With Artemether-lumefantrine on Antimalarial Exposure and Reinfection Risks in Ugandan Children With Uncomplicated Malaria: A Randomized Controlled Trial

BACKGROUND

Artemether-lumefantrine (AL) is the most widely used artemisinin-based combination therapy in Sub-Saharan Africa and is threatened by the emergence of artemisinin resistance. Dosing is suboptimal in young children. We hypothesized that extending AL duration will improve exposure and reduce reinfection risks.

METHODS

We conducted a prospective, randomized, open-label pharmacokinetic/pharmacodynamic study of extended duration AL in children with malaria in high-transmission rural Uganda. Children received 3-day (standard 6-dose) or 5-day (10-dose) AL with sampling for artemether, dihydroartemisinin, and lumefantrine over 42-day clinical follow-up. Primary outcomes were (1) comparative pharmacokinetic parameters between regimens and (2) recurrent parasitemia analyzed as intention-to-treat.

RESULTS

A total of 177 children aged 16 months to 16 years were randomized, contributing 227 total episodes. Terminal median lumefantrine concentrations were significantly increased in the 5-day versus 3-day regimen on days 7, 14, and 21 (P < .001). A predefined day 7 lumefantrine threshold of 280 ng/mL was strongly predictive of recurrence risk at 28 and 42 days (P < .001). Kaplan-Meier estimated 28-day (51% vs 40%) and 42-day risk (75% vs 68%) did not significantly differ between 3- and 5-day regimens. No significant toxicity was seen with the extended regimen.

CONCLUSIONS

Extending the duration of AL was safe and significantly enhanced overall drug exposure in young children but did not lead to significant reductions in recurrent parasitemia risk in our high-transmission setting. However, day 7 levels were strongly predictive of recurrent parasitemia risk, and those in the lowest weight-band were at higher risk of underdosing with the standard 3-day regimen.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov number NCT03453840.

Polyester Nanocapsules for Intravenous Delivery of Artemether: Formulation Development, Antimalarial Efficacy, and Cardioprotective Effects In Vivo

Artemether (ATM) is an effective antimalarial drug that also has a short half-life in the blood. Furthermore, ATM is also cardiotoxic and is associated with pro-arrhythmogenic risks. We aimed to develop a delivery system enabling the prolonged release of ATM into the blood coupled with reduced cardiotoxicity. To achieve this, we prepared polymeric nanocapsules (NCs) from different biodegradable polyesters, namely poly(D,L-lactide) (PLA), poly-ε-caprolactone (PCL), and surface-modified NCs, using a monomethoxi-polyethylene glycol-block-poly(D,L-lactide) (PEG5kDa-PLA45kDa) polymer. Using this approach, we were able to encapsulate high yields of ATM (>85%, 0−4 mg/mL) within the oily core of the NCs. The PCL-NCs exhibited the highest percentage of ATM loading as well as a slow release rate. Atomic force microscopy showed nanometric and spherical particles with a narrow size dispersion. We used the PCL NCs loaded with ATM for biological evaluation following IV administration. As with free-ATM, the ATM-PCL-NCs formulation exhibited potent antimalarial efficacy using either the “Four-day test” protocol (ATM total at the end of the 4 daily doses: 40 and 80 mg/kg) in Swiss mice infected with P. berghei or a single low dose (20 mg/kg) of ATM in mice with higher parasitemia (15%). In healthy rats, IV administration of single doses of free-ATM (40 or 80 mg/kg) prolonged cardiac QT and QTc intervals and induced both bradycardia and hypotension. Repeated IV administration of free-ATM (four IV doses at 20 mg/kg every 12 h for 48 h) also prolonged the QT and QTc intervals but, paradoxically, induced tachycardia and hypertension. Remarkably, the incorporation of ATM in ATM-PCL-NCs reduced all adverse effects. In conclusion, the encapsulation of ATM in biodegradable polyester NCs reduces its cardiovascular toxicity without affecting its antimalarial efficacy.

The pharmacokinetic properties of artemether and lumefantrine in Malaysian patients with Plasmodium knowlesi malaria

AIMS

The aim of this study was to assess the pharmacokinetic properties of artemether, lumefantrine and their active metabolites in Plasmodium knowlesi malaria.

METHODS

Malaysian adults presenting with uncomplicated P. knowlesi infections received six doses of artemether (1.7 mg/kg) plus lumefantrine (10 mg/kg) over 3 days. Venous blood and dried blood spot (DBS) samples were taken at predetermined time-points over 28 days. Plasma and DBS artemether, dihydroartemisinin, lumefantrine and desbutyl-lumefantrine were measured using liquid chromatography-mass spectrometry. Multi-compartmental population pharmacokinetic models were developed using plasma with or without DBS drug concentrations.

RESULTS

Forty-one participants (mean age 45 years, 66% males) were recruited. Artemether-lumefantrine treatment was well tolerated and parasite clearance was prompt. Plasma and DBS lumefantrine concentrations were in close agreement and were used together in pharmacokinetic modelling, but only plasma concentrations of the other analytes were used because of poor correlation with DBS levels. The areas under the concentration-time curve (AUC_0-∞ ) for artemether, dihydroartemisinin and lumefantrine (medians 1626, 1881 and 625 098 μg.h/L, respectively) were similar to those reported in previous pharmacokinetic studies in adults and children. There was evidence of auto-induction of artemether metabolism (mean increase in clearance relative to bioavailability 25.2% for each subsequent dose). The lumefantrine terminal elimination half-life (median 9.5 days) was longer than reported in healthy volunteers and adults with falciparum malaria.

CONCLUSION

The disposition of artemether, dihydroartemisinin and lumefantrine in knowlesi malaria largely parallels that in other human malarias. DBS lumefantrine concentrations can be used in pharmacokinetic studies but DBS technology is currently unreliable for the other analytes.

Population Pharmacokinetics of Artemether, Dihydroartemisinin, and Lumefantrine in Rwandese Pregnant Women Treated for Uncomplicated Plasmodium falciparum Malaria

The artemisinin-based combination therapy artemether-lumefantrine is commonly used in pregnant malaria patients. However, the effect of pregnancy-related changes on exposure is unclear, and pregnancy has been associated with decreased efficacy in previous studies. This study aimed to characterize the population pharmacokinetics of artemether, its active metabolite dihydroartemisinin, and lumefantrine in 22 Rwandese pregnant women in their second (n = 11) or third (n = 11) trimester with uncomplicated Plasmodium falciparum malaria. These patients were enrolled from Rwamagana district hospital and received the standard fixed oral dose combination of 80 mg of artemether and 480 mg of lumefantrine twice daily for 3 days. Venous plasma concentrations were quantified for all three analytes using liquid chromatography coupled with tandem mass spectroscopy, and data were analyzed using nonlinear mixed-effects modeling. Lumefantrine pharmacokinetics was described by a flexible but highly variable absorption, with a mean absorption time of 4.04 h, followed by a biphasic disposition model. The median area under the concentration-time curve from 0 h to infinity (AUC_0-∞) for lumefantrine was 641 h · mg/liter. Model-based simulations indicated that 11.7% of the study population did not attain the target day 7 plasma concentration (280 ng/ml), a threshold associated with increased risk of recrudescence. The pharmacokinetics of artemether was time dependent, and the autoinduction of its clearance was described using an enzyme turnover model. The turnover half-life was predicted to be 30.4 h. The typical oral clearance, which started at 467 liters/h, increased 1.43-fold at the end of treatment. Simulations suggested that lumefantrine pharmacokinetic target attainment appeared to be reassuring in Rwandese pregnant women, particularly compared to target attainment in Southeast Asia. Larger cohorts will be required to confirm this finding.

Toxicokinetics and Hydrolysis of Artelinate and Artesunate in Malaria-Infected Rats

Comparative toxicokinetic (TK) and hydrolysis studies of intravenously administered two new antimalarial agents, artelinate (AL) and artesunate (AS), were performed in malaria-infected rats using three daily equimolar doses (96 μmoles/kg). The TK evaluation was related to select one drug for severe malaria treatment in U.S. Army. Drug concentration of AS with daily dose of 36.7 mg/kg was one-third less on day 3 than on day 1, which resembled its active metabolite, dihydroartemisinin (DHA), suggesting an autoinduction of hepatic drug-metabolizing enzymes for AS. The results were similar to other artemisinin drugs, but not for AL. TK parameters of AL were very comparable from day 1 to day 3 at same AS molecular dose at 40.6 mg/kg. AS is the prodrug of DHA with the DHA/AS ratio of 5.26 compared to the ratio of 0.01 for DHA/AL. Other TK parameters revealed that the total AUC1–3 days (84.4 μg · h ml−1) of AL was fivefold higher than that of AS (15.7 mu;g h ml−1 of AS plus DHA). The elimination half-life of AL (7.1 h) was much longer than that of AS (0.36 h) or DHA (0.72 h). The remarkable alteration of the TK shape of AL may be caused by poor conversion rates to DHA and an enterohepatic circulation, which is confirmed by the present TK and tissue distribution studies. Compared to AS, higher drug exposure levels and longer exposure time of AL in the rat blood may be the cause of its increased toxicity.

Endoperoxide Drug Cross-Resistance Patterns for Plasmodium falciparum Exhibiting an Artemisinin Delayed-Clearance Phenotype

The ring-stage susceptibility assay was modified to quantify the susceptibilities of multiple strains of control and delayed-clearance phenotype (DCP) Plasmodium falciparum strains to seven endoperoxide antimalarial drugs. The susceptibility of all of the DCP lines to six of the drugs was lower than that of the controls. In contrast, DCP parasites did not show reduced susceptibility to the synthetic endoperoxide drug OZ439. These data show that it is possible to circumvent emerging artemisinin resistance with a modified endoperoxide drug.

The interaction between artemether-lumefantrine and lopinavir/ritonavir-based antiretroviral therapy in HIV-1 infected patients

Background

Artemether-lumefantrine is currently the most widely recommended treatment of uncomplicated malaria. Lopinavir–based antiretroviral therapy is the commonly recommended second-line HIV treatment. Artemether and lumefantrine are metabolised by cytochrome P450 isoenzyme CYP3A4, which lopinavir/ritonavir inhibits, potentially causing clinically important drug-drug interactions.

Methods

An adaptive, parallel-design safety and pharmacokinetic study was conducted in HIV-infected (malaria-negative) patients: antiretroviral-naïve and those stable on lopinavir/ritonavir-based antiretrovirals. Both groups received the recommended six-dose artemether-lumefantrine treatment. The primary outcome was day-7 lumefantrine concentrations, as these correlate with antimalarial efficacy. Adverse events were solicited throughout the study, recording the onset, duration, severity, and relationship to artemether-lumefantrine.

Results

We enrolled 34 patients. Median day-7 lumefantrine concentrations were almost 10-fold higher in the lopinavir than the antiretroviral-naïve group [3170 versus 336 ng/mL; p = 0.0001], with AUC_(0-inf) and C_max increased five-fold [2478 versus 445 μg.h/mL; p = 0.0001], and three-fold [28.2 versus 8.8 μg/mL; p < 0.0001], respectively. Lumefantrine C_max, and AUC_(0-inf) increased significantly with mg/kg dose in the lopinavir, but not the antiretroviral-naïve group. While artemether exposure was similar between groups, C_max and AUC_(0-8h) of its active metabolite dihydroartemisinin were initially two-fold higher in the lopinavir group [p = 0.004 and p = 0.0013, respectively]. However, this difference was no longer apparent after the last artemether-lumefantrine dose. Within 21 days of starting artemether-lumefantrine there were similar numbers of treatment emergent adverse events (42 vs. 35) and adverse reactions (12 vs. 15, p = 0.21) in the lopinavir and antiretroviral-naïve groups, respectively. There were no serious adverse events and no difference in electrocardiographic QTcF- and PR-intervals, at the predicted lumefantrine T_max.

Conclusion

Despite substantially higher lumefantrine exposure, intensive monitoring in our relatively small study raised no safety concerns in HIV-infected patients stable on lopinavir-based antiretroviral therapy given the recommended artemether-lumefantrine dosage. Increased day-7 lumefantrine concentrations have been shown previously to reduce the risk of malaria treatment failure, but further evidence in adult patients co-infected with malaria and HIV is needed to assess the artemether-lumefantrine risk : benefit profile in this vulnerable population fully. Our antiretroviral-naïve patients confirmed previous findings that lumefantrine absorption is almost saturated at currently recommended doses, but this dose-limited absorption was overcome in the lopinavir group.

Trial registration

Clinical Trial Registration number NCT00869700. Registered on clinicaltrials.gov 25 March 2009

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1345-1) contains supplementary material, which is available to authorized users.

Artemether-lumefantrine co-administration with antiretrovirals: population pharmacokinetics and dosing implications

AIM

Drug–drug interactions between antimalarial and antiretroviral drugs may influence antimalarial treatment outcomes. The aim of this study was to investigate the potential drug–drug interactions between the antimalarial drugs, lumefantrine, artemether and their respective metabolites desbutyl-lumefantrine and dihydroartemisinin, and the HIV drugs efavirenz, nevirapine and lopinavir/ritonavir.

METHOD

Data from two clinical studies, investigating the influence of the HIV drugs efavirenz, nevirapine and lopinavir/ritonavir on the pharmacokinetics of the antimalarial drugs lumefantrine, artemether and their respective metabolites, in HIV infected patients were pooled and analyzed using a non-linear mixed effects modelling approach.

RESULTS

Efavirenz and nevirapine significantly decreased the terminal exposure to lumefantrine (decrease of 69.9% and 25.2%, respectively) while lopinavir/ritonavir substantially increased the exposure (increase of 439%). All antiretroviral drugs decreased the total exposure to dihydroartemisinin (decrease of 71.7%, 41.3% and 59.7% for efavirenz, nevirapine and ritonavir/lopinavir, respectively). Simulations suggest that a substantially increased artemether-lumefantrine dose is required to achieve equivalent exposures when co-administered with efavirenz (250% increase) and nevirapine (75% increase). When co-administered with lopinavir/ritonavir it is unclear if the increased lumefantrine exposure compensates adequately for the reduced dihydroartemisinin exposure and thus whether dose adjustment is required.

CONCLUSION

There are substantial drug interactions between artemether-lumefantrine and efavirenz, nevirapine and ritonavir/lopinavir. Given the readily saturable absorption of lumefantrine, the dose adjustments predicted to be necessary will need to be evaluated prospectively in malaria-HIV co-infected patients.

Gametocyte Clearance Kinetics Determined by Quantitative Magnetic Fractionation in Melanesian Children with Uncomplicated Malaria Treated with Artemisinin Combination Therapy

Quantitative magnetic fractionation and a published mathematical model were used to characterize between-treatment differences in gametocyte density and prevalence in 70 Papua New Guinean children with uncomplicated Plasmodium falciparum and/or Plasmodium vivax malaria randomized to one of two artemisinin combination therapies (artemether-lumefantrine or artemisinin-naphthoquine) in an intervention trial. There was an initial rise in peripheral P. falciparum gametocyte density with both treatments, but it was more pronounced in the artemisinin-naphthoquine group. Model-derived estimates of the median pretreatment sequestered gametocyte population were 21/μl for artemether-lumefantrine and 61/μl for artemisinin-naphthoquine (P < 0.001). The median time for P. falciparum gametocyte density to fall to <2.5/μl (below which transmission becomes unlikely) was 16 days in the artemether-lumefantrine group and 20 days in artemisinin-naphthoquine group (P < 0.001). Gametocyte prevalence modeling suggested that artemisinin-naphthoquine-treated children became gametocytemic faster (median, 2.2 days) than artemether-lumefantrine-treated children (median, 5.3 days; P < 0.001) and had a longer median P. falciparum gametocyte carriage time per individual (20 versus 13 days; P < 0.001). Clearance of P. vivax gametocytes was rapid (within 3 days) in both groups; however, consistent with the reappearance of asexual forms in the main trial, nearly 40% of children in the artemether-lumefantrine group developed P. vivax gametocytemia between days 28 and 42 compared with 3% of children in the artemisinin-naphthoquine group. These data suggest that artemisinin is less active than artemether against sequestered gametocytes. Greater initial gametocyte release after artemisinin-naphthoquine increases the period of potential P. falciparum transmission by 4 days relative to artemether-lumefantrine, but the longer elimination half-life of naphthoquine than of lumefantrine suppresses P. vivax recurrence and consequent gametocytemia.

Pharmacokinetics of a novel sublingual spray formulation of the antimalarial drug artemether in African children with malaria

The pharmacokinetics of sublingual artemether (ArTiMist) was investigated in 91 young African children with severe malaria or who could not tolerate oral antimalarial therapy. Each received 3.0 mg/kg of body weight of artemether at 0, 8, 24, 36, 48, and 60 h or until the initiation of oral treatment. Few blood samples were drawn postdose. Plasma artemether and dihydroartemisinin (DHA) levels were measured using liquid chromatography-mass spectrometry, and the data were analyzed using established population compartmental pharmacokinetic models. Parasite clearance was prompt (median parasite clearance time, 24 h), and there were no serious adverse events. Consistent with studies in healthy adults (S. Salman, D. Bendel, T. C. Lee, D. Templeton, and T. M. E. Davis, Antimicrob Agents Chemother 59:3197-3207, 2015, http://dx.doi.org/10.1128/AAC.05013-14), the absorption of sublingual artemether was biphasic, and multiple dosing was associated with the autoinduction of the metabolism of artemether to DHA (which itself has potent antimalarial activity). In contrast to studies using healthy volunteers, pharmacokinetic modeling indicated that the first absorption phase did not avoid first-pass metabolism, suggesting that the drug is transferred to the upper intestine through postdose fluid/food intake. Simulations using the present data and those from an earlier study in older Melanesian children with uncomplicated malaria treated with artemether-lumefantrine tablets suggested that the bioavailability of sublingual artemether was at least equivalent to that after conventional oral artemether-lumefantrine (median [interquartile range] areas under the concentration-time curve for artemether, 3,403 [2,471 to 4,771] versus 3,063 [2,358 to 4,514] μg · h/liter, respectively; and for DHA, 2,958 [2,146 to 4,278] versus 2,839 [1,812 to 3,488] μg · h/liter, respectively; P ≥ 0.42). These findings suggest that sublingual artemether could be used as prereferral treatment for sick children before transfer for definitive management of severe or moderately severe malaria.

Pharmacokinetics of a novel sublingual spray formulation of the antimalarial drug artemether in healthy adults

The pharmacokinetics of sublingual artemether (ArTiMist) was investigated in two open-label studies. In study 1, 16 healthy males were randomized to each of four single-dose treatments administered in random order: (i) 15.0 mg of sublingual artemether (5 × 3.0 actuations), (ii) 30.0 mg of sublingual artemether (10 × 3.0 mg), (iii) 30.0 mg of sublingual artemether (5 × 6.0 mg), and (iv) 30.0 mg of artemether in tablet form. In study 2, 16 healthy males were randomized to eight 30.0-mg doses of sublingual artemether given over 5 days as either 10 3.0-mg or 5 6.0-mg actuations. Frequent blood samples were drawn postdose. Plasma artemether and dihydroartemisinin levels were measured using liquid chromatography-mass spectrometry. Population compartmental pharmacokinetic models were developed. In study 1, sublingual artemether absorption was biphasic, with both rate constants being greater than that of the artemether tablets (1.46 and 1.66 versus 0.43/h, respectively). Relative to the tablets, sublingual artemether had greater bioavailability (≥1.24), with the greatest relative bioavailability occurring in the 30.0-mg dose groups (≥1.58). In study 2, there was evidence that the first absorption phase accounted for between 32% and 69% of the total dose and avoided first-pass (FP) metabolism, with an increase in FP metabolism occurring in later versus earlier doses but with no difference in bioavailability between the dose actuations. Sublingual artemether is more rapidly and completely absorbed than are equivalent doses of artemether tablets in healthy adults. Its disposition appears to be complex, with two absorption phases, the first representing pregastrointestinal absorption, as well as dose-dependent bioavailability and autoinduction of metabolism with multiple dosing.

The effect of UGTs polymorphism on the auto-induction phase II metabolism-mediated pharmacokinetics of dihydroartemisinin in healthy Chinese subjects after oral administration of a fixed combination of dihydroartemisinin-piperaquine

BACKGROUND

Dihydroartemisinin (DHA) is a component of artemisinin-based combination therapy (ACT), which is widely recommended for treatment of uncomplicated falciparum malaria. DHA is also the main metabolite of artemether and artesunate, both of which are used in ACT. Due to auto-induction metabolism, declining plasma concentrations after the repeated dosing have been reported for artemisinin (Qing-hao-su) and artemether. This study was designed to evaluate the potential auto-induction metabolism of DHA in healthy Chinese adults after multiple oral doses of DHA. The polymorphic effects of UGT1A9 (I399C>T) and UGT2B7*2 (802C>T), the major enzymes involved in the metabolism of DHA, on the pharmacokinetic profiles of DHA and its metabolite was also studied.

METHODS

Sixteen healthy Chinese subjects (four I399TT/802CC, four I399CC/802TT, four I399TT/802TT and four I399CT/802CT) received four recommended oral doses of Artekin, an ACT containing DHA (80 mg/dose) and piperaquine (PQ; 640 mg/dose), at 0, 6, 24 and 32 h. Plasma samples were analysed for DHA and its metabolite using a validated liquid chromatography tandem mass spectrometric (LC-MS) method.

RESULTS

DHA and its glucuronidated metabolite DHA-Glu were detected in human plasma after oral administration of DHA-PQ. Compared with the first dose, the AUC0-t of the parent drug DHA decreased significantly (P<0.01) with increased oral clearance (CL/F) after each repeated dose of DHA-PQ, whereas its metabolite DHA-Glu did not change (P>0.05) in AUC(0-t) or C(max). The phase II metabolic capability, calculated by the AUC(0-t) ratio of DHA-Glu to the parent drug DHA, increased 1.5-fold (90% CI, 1.3-1.7), 1.2-fold (90% CI, 1.1-1.3) and 1.7-fold (90% CI, 1.5-1.8) after the second, third and fourth dose, respectively. No polymorphic effect was found for UGT1A9 (I399C>T) and UGT2B7*2 (802C>T) on the pharmacokinetic profiles of DHA and its metabolite DHA-Glu.

CONCLUSIONS

The auto-induction phase II metabolism of DHA was present in healthy Chinese subjects after the recommended two-day oral doses of DHA-PQ (Artekin). The metabolic capability could recover after a 12-h dosing interval, which suggested that the alternative common three-day regimen (once daily) for DHA-PQ could probably lead to higher bioavailability of DHA. The polymorphism of UGT1A9 (I399C>T) and UGT2B7*2 (802C>T) may not be a concern during the treatment with DHA.

Artemisinin-naphthoquine versus artemether-lumefantrine for uncomplicated malaria in Papua New Guinean children: an open-label randomized trial

BACKGROUND

Artemisinin combination therapies (ACTs) with broad efficacy are needed where multiple Plasmodium species are transmitted, especially in children, who bear the brunt of infection in endemic areas. In Papua New Guinea (PNG), artemether-lumefantrine is the first-line treatment for uncomplicated malaria, but it has limited efficacy against P. vivax. Artemisinin-naphthoquine should have greater activity in vivax malaria because the elimination of naphthoquine is slower than that of lumefantrine. In this study, the efficacy, tolerability, and safety of these ACTs were assessed in PNG children aged 0.5-5 y.

METHODS AND FINDINGS

An open-label, randomized, parallel-group trial of artemether-lumefantrine (six doses over 3 d) and artemisinin-naphthoquine (three daily doses) was conducted between 28 March 2011 and 22 April 2013. Parasitologic outcomes were assessed without knowledge of treatment allocation. Primary endpoints were the 42-d P. falciparum PCR-corrected adequate clinical and parasitologic response (ACPR) and the P. vivax PCR-uncorrected 42-d ACPR. Non-inferiority and superiority designs were used for falciparum and vivax malaria, respectively. Because the artemisinin-naphthoquine regimen involved three doses rather than the manufacturer-specified single dose, the first 188 children underwent detailed safety monitoring. Of 2,542 febrile children screened, 267 were randomized, and 186 with falciparum and 47 with vivax malaria completed the 42-d follow-up. Both ACTs were safe and well tolerated. P. falciparum ACPRs were 97.8% and 100.0% in artemether-lumefantrine and artemisinin-naphthoquine-treated patients, respectively (difference 2.2% [95% CI -3.0% to 8.4%] versus -5.0% non-inferiority margin, p = 0.24), and P. vivax ACPRs were 30.0% and 100.0%, respectively (difference 70.0% [95% CI 40.9%-87.2%], p<0.001). Limitations included the exclusion of 11% of randomized patients with sub-threshold parasitemias on confirmatory microscopy and direct observation of only morning artemether-lumefantrine dosing.

CONCLUSIONS

Artemisinin-naphthoquine is non-inferior to artemether-lumefantrine in PNG children with falciparum malaria but has greater efficacy against vivax malaria, findings with implications in similar geo-epidemiologic settings within and beyond Oceania.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12610000913077. Please see later in the article for the Editors' Summary.

Population pharmacokinetics of artesunate and dihydroartemisinin during long-term oral administration of artesunate to patients with metastatic breast cancer

PURPOSE

The purpose of this study were firstly to characterize the population pharmacokinetics of artesunate (ARS) and its active metabolite dihydroartemisinin (DHA) in patients with metastatic breast cancer during long-term (>3 weeks) daily oral ARS administration and secondly to study the relationship between salivary and plasma concentrations of DHA.

METHODS

Drug concentration-time data from 23 patients, receiving oral ARS (100, 150, or 200 mg OD), was analyzed using nonlinear mixed effects modeling. A combined drug-metabolite population pharmacokinetic model was developed to describe the plasma pharmacokinetics of ARS and DHA in plasma. Saliva drug concentrations were incorporated as being directly proportional to plasma concentrations.

RESULTS

A first-order absorption model for ARS linked to a combined two-compartment disposition model for ARS and one-compartment disposition model for DHA provided the best fit to the data. No covariates were identified that could explain between-subject variability. A time-dependent increase in apparent elimination clearance of DHA was observed. Salivary DHA concentrations were proportionally correlated with total DHA plasma concentrations, with an estimated slope factor of 0.116.

CONCLUSIONS

Population pharmacokinetics of ARS and DHA in patients with breast cancer was well described by a combined drug-metabolite model without any covariates and with an increase in apparent elimination clearance of DHA over time. The estimated DHA saliva/plasma ratio was in good agreement with the reported DHA unbound fraction in human plasma. Saliva ARS concentrations correlated poorly with plasma concentrations. This suggests the use of saliva sampling for therapeutic drug monitoring of DHA. However, further studies are warranted to investigate the robustness of this approach.

Clinical pharmacokinetic drug interactions associated with artemisinin derivatives and HIV-antivirals

Management of HIV and malaria co-infection is challenging due to potential drug-drug interactions between antimalarial and HIV-antiviral drugs. Little is known of the clinical significance of these drug interactions, and this review provides a comprehensive summary and critical evaluation of the literature. Specifically, drug interactions between WHO-recommended artemisinin combination therapies (ACT) and HIV-antivirals are discussed. An extensive literature search produced eight articles detailing n = 44 individual pharmacokinetic interactions. Only data pertaining to artemether-lumefantrine and two other artesunate combinations are available, but most of the interactions are characterized on at least two occasions by two different groups. Overall, protease inhibitors (PIs) tended to increase the exposure of lumefantrine and decrease the exposures of artemether and dihydroartemisinin, a pharmacologically active metabolite of artemether. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) tended to decrease the exposures of artemether, dihydroartemisinin, and lumefantrine when co-administered with artemether-lumefantrine. Fewer studies characterized the effects of PIs or NNRTIs on artesunate combinations, but nevirapine increased artesunate exposure and ritonavir decreased dihydroartemisinin exposure. On the other hand, artemether-lumefantrine or artesunate combinations had little effect on the pharmacokinetics of HIV-antivirals, with the exception of decreased nevirapine exposure from artemether-lumefantrine or increased ritonavir exposure from pyronaridine/artesunate co-administration. In general, pharmacokinetic interactions can be explained by the metabolic properties of the co-administered drugs. Despite several limitations to the studies, these data do provide valuable insights into the potential pharmacokinetic perturbations, and the consistently marked elevation or reduction in ACT exposure in some cases cannot be overlooked.

Coartemether (artemether and lumefantrine): an oral antimalarial drug

Coartemether (Riamet, Coartem, Novartis), a tablet formulation of artemether and lumefantrine, is a well-tolerated, fast-acting and effective blood schizontocidal drug that serves primarily in the treatment of uncomplicated falciparum malaria that is resistant to other antimalarials. Initial clinical-parasitological response relies mainly on the artemether component, while lumefantrine effects radical cure. The absorption of lumefantrine is poor during the fasting state, the normal condition in acutely ill malaria patients, but with return to normal diet it becomes adequate. This highlights the need for an appropriate adjustment of the dose regimen. In the area where Plasmodium falciparum shows the highest degree of multidrug resistance worldwide, the best results (99% cure) were obtained with a six-dose regimen given over 5 days. Extensive cardiological investigations have demonstrated the high cardiac safety of coartemether.

Modeling within-host effects of drugs on Plasmodium falciparum transmission and prospects for malaria elimination

Achieving a theoretical foundation for malaria elimination will require a detailed understanding of the quantitative relationships between patient treatment-seeking behavior, treatment coverage, and the effects of curative therapies that also block Plasmodium parasite transmission to mosquito vectors. Here, we report a mechanistic, within-host mathematical model that uses pharmacokinetic (PK) and pharmacodynamic (PD) data to simulate the effects of artemisinin-based combination therapies (ACTs) on Plasmodium falciparum transmission. To contextualize this model, we created a set of global maps of the fold reductions that would be necessary to reduce the malaria R C (i.e. its basic reproductive number under control) to below 1 and thus interrupt transmission. This modeling was applied to low-transmission settings, defined as having a R 0<10 based on 2010 data. Our modeling predicts that treating 93-98% of symptomatic infections with an ACT within five days of fever onset would interrupt malaria transmission for ∼91% of the at-risk population of Southeast Asia and ∼74% of the global at-risk population, and lead these populations towards malaria elimination. This level of treatment coverage corresponds to an estimated 81-85% of all infected individuals in these settings. At this coverage level with ACTs, the addition of the gametocytocidal agent primaquine affords no major gains in transmission reduction. Indeed, we estimate that it would require switching ∼180 people from ACTs to ACTs plus primaquine to achieve the same transmission reduction as switching a single individual from untreated to treated with ACTs. Our model thus predicts that the addition of gametocytocidal drugs to treatment regimens provides very small population-wide benefits and that the focus of control efforts in Southeast Asia should be on increasing prompt ACT coverage. Prospects for elimination in much of Sub-Saharan Africa appear far less favorable currently, due to high rates of infection and less frequent and less rapid treatment.

Improving pharmacokinetic-pharmacodynamic modeling to investigate anti-infective chemotherapy with application to the current generation of antimalarial drugs

Mechanism-based pharmacokinetic-pharmacodynamic (PK/PD) modelling is the standard computational technique for simulating drug treatment of infectious diseases with the potential to enhance our understanding of drug treatment outcomes, drug deployment strategies, and dosing regimens. Standard methodologies assume only a single drug is used, it acts only in its unconverted form, and that oral drugs are instantaneously absorbed across the gut wall to their site of action. For drugs with short half-lives, this absorption period accounts for a significant period of their time in the body. Treatment of infectious diseases often uses combination therapies, so we refined and substantially extended the PK/PD methodologies to incorporate (i) time lags and drug concentration profiles resulting from absorption across the gut wall and, if required, conversion to another active form; (ii) multiple drugs within a treatment combination; (iii) differing modes of action of drugs in the combination: additive, synergistic, antagonistic; (iv) drugs converted to an active metabolite with a similar mode of action. This methodology was applied to a case study of two first-line malaria treatments based on artemisinin combination therapies (ACTs, artemether-lumefantrine and artesunate-mefloquine) where the likelihood of increased artemisinin tolerance/resistance has led to speculation on their continued long-term effectiveness. We note previous estimates of artemisinin kill rate were underestimated by a factor of seven, both the unconverted and converted form of the artemisinins kill parasites and the extended PK/PD methodology produced results consistent with field observations. The simulations predict that a potentially rapid decline in ACT effectiveness is likely to occur as artemisinin resistance spreads, emphasising the importance of containing the spread of artemisinin resistance before it results in widespread drug failure. We found that PK/PD data is generally very poorly reported in the malaria literature, severely reducing its value for subsequent re-application, and we make specific recommendations to improve this situation.

A Study on Course of Infection and Haematological Changes in falciparum-Infected in Comparison with Artemisinin(s)-Treated Mice

To find out the efficacy and effect of artemisinin derivatives on haematological indices, C57BL/6J mice were challenged with Plasmodium falciparum and treated with therapeutic doses of AS, AE, and AL. Course of infection was studied in the infected and treated groups up to day 42. Peak level of parasitaemia (38%) was observed on day 11 in infected group. Haematological indices indicated significant (P < 0.05) decrease in RBC, WBC, haemoglobin, packed cell volume, mean cell volume, and platelet counts in infected mice. But all the parameters were restored to normal values, and significant (P < 0.05) changes were observed in all drug-treated groups. Insignificant changes were observed for MCHC (P > 0.05) in all drug-treated groups. Percent of peak parasitaemia was much reduced in AL- (3.2% on day 3) treated group in comparison with AE- (2.4% on day 4) and AS- (4% on day 2) treated groups. Parasites were completely cleared on day 6 in AS group, day 5 in AE group, and day 4 in AL group. Hence, our results strongly support that combination therapy has high efficacy rates than monotherapy. No adverse effects were observed on haematological parameters when animals were treated with therapeutic dosages.

An investigation of the auto-induction of and gender-related variability in the pharmacokinetics of dihydroartemisinin in the rat

Background

Artemisinin (QHS) and its derivatives dihydroartemisinin (DHA), artemether and artesunate have become the first-line anti-malarials in areas of multidrug resistance. Declining plasma concentrations during the repeated dosing have been reported for QHS, artemether and less convincingly for artesunate (ARS). However, there is limited information on whether the concentrations of their active metabolite DHA and its subsequent metabolites increased after multiple drug administrations. This study was designed to evaluate the potential auto-induction metabolism of DHA in animal species. The sex-specific effect on the pharmacokinetic profiles of DHA and its metabolites was studied. The pharmacokinetics of ARS, the prodrug of DHA, and its phase I/II metabolites were also investigated.

Methods

Two groups of rats received a single oral dose of DHA or ARS, and another two groups of rats were given oral doses of DHA or ARS once daily for five consecutive days. Plasma samples were analyzed for DHA, ARS and their phase I/II metabolites, using a validated liquid chromatography tandem mass spectrometric (LC-MS) method.

Results

DHA, monohydroxylated DHA (M1) and the glucuronide of DHA (DHA-G) were detected in rat plasma after oral administration of DHA or ARS. Neither DHA nor its metabolites (M1 and DHA-G) changed significantly (P > 0.05) in AUC_0-t after 5-day oral doses of DHA or ARS. Sex difference was observed for DHA and its metabolites (M1 and DHA-G), whereas its prodrug ARS did not show similar characteristics for the corresponding metabolites (DHA, M1 and DHA-G).

Conclusions

The results gave the direct evidence for the absence of auto-induction of phase I and phase II metabolism of DHA and ARS in rats. The sex effect existed for DHA but not for ARS, which could be caused by the sex-specific differences in absorption of DHA.

First-time comparison of the in vitro antimalarial activity of Artemisia annua herbal tea and artemisinin

Artemisia annua tea has been proven to be a very effective treatment for malaria in various clinical trials, but to date its efficacy has not been investigated in vitro. A study was therefore performed to evaluate the effects of A. annua tea on Plasmodium falciparum cultures in vitro. The concentration of artemisinin in the herbal tea preparation was also determined. The herbal tea extract was tested against chloroquine (CQ)-sensitive D10 and CQ-resistant W2 strains of P. falciparum using the parasite lactate dehydrogenase assay. Quantification of artemisinin in the extract of leaves of A. annua was performed using proton nuclear magnetic resonance ((1)H-NMR). Results of the in vitro tests were consistent with the clinical efficacy of A. annua tea [50% inhibitory concentration (IC(50)) for strain D10=1.11±0.21 μg/ml; IC(50) for strain W2=0.88±0.35 μg/ml]. The concentration of artemisinin in A. annua tea (0.18±0.02% of dry weight) was far too low to be responsible for the antimalarial activity. The artemisinin present in the tea is probably co-solubilised with other ingredients, some of which also have antimalarial activity and act synergistically with it. These compounds also merit further research to determine whether their presence hinders the development of parasite resistance compared with pure artemisinin.

Significant pharmacokinetic interactions between artemether/lumefantrine and efavirenz or nevirapine in HIV-infected Ugandan adults

OBJECTIVES

Co-administration of artemether/lumefantrine with antiretroviral therapy has potential for pharmacokinetic drug interactions. We investigated drug-drug interactions between artemether/lumefantrine and efavirenz or nevirapine.

METHODS

We performed a cross-over study in which HIV-infected adults received standard six-dose artemether/lumefantrine 80/480 mg before and at efavirenz or nevirapine steady state. Artemether, dihydroartemisinin, lumefantrine, efavirenz and nevirapine plasma concentrations were measured and compared.

RESULTS

Efavirenz significantly reduced artemether maximum concentration (C(max)) and plasma AUC (median 29 versus 12 ng/mL, P < 0.01, and 119 versus 25 ng · h/mL, P < 0.01), dihydroartemisinin C(max) and AUC (median 120 versus 26 ng/mL, P < 0.01, and 341 versus 84 ng · h/mL, P < 0.01), and lumefantrine C(max) and AUC (median 8737 versus 6331 ng/mL, P = 0.03, and 280 370 versus 124 381 ng · h/mL, P < 0.01). Nevirapine significantly reduced artemether C(max) and AUC (median 28 versus 11 ng/mL, P < 0.01, and 123 versus 34 ng · h/mL, P < 0.01) and dihydroartemisinin C(max) and AUC (median 107 versus 59 ng/mL, P < 0.01, and 364 versus 228 ng · h/mL, P < 0.01). Lumefantrine C(max) and AUC were non-significantly reduced by nevirapine. Artemether/lumefantrine reduced nevirapine C(max) and AUC (median 8620 versus 4958 ng/mL, P < 0.01, and 66 329 versus 35 728 ng · h/mL, P < 0.01), but did not affect efavirenz exposure.

CONCLUSIONS

Co-administration of artemether/lumefantrine with efavirenz or nevirapine resulted in a reduction in artemether, dihydroartemisinin, lumefantrine and nevirapine exposure. These drug interactions may increase the risk of malaria treatment failure and development of resistance to artemether/lumefantrine and nevirapine. Clinical data from population pharmacokinetic and pharmacodynamic trials evaluating the impact of these drug interactions are urgently needed.

Population pharmacokinetics of Artemether and dihydroartemisinin in pregnant women with uncomplicated Plasmodium falciparum malaria in Uganda

Background

Malaria in pregnancy increases the risk of maternal anemia, abortion and low birth weight. Approximately 85.3 million pregnancies occur annually in areas with Plasmodium falciparum transmission. Pregnancy has been reported to alter the pharmacokinetic properties of many anti-malarial drugs. Reduced drug exposure increases the risk of treatment failure. The objective of this study was to evaluate the population pharmacokinetic properties of artemether and its active metabolite dihydroartemisinin in pregnant women with uncomplicated P. falciparum malaria in Uganda.

Methods

Twenty-one women with uncomplicated P. falciparum malaria in the second and third trimesters of pregnancy received the fixed oral combination of 80 mg artemether and 480 mg lumefantrine twice daily for three days. Artemether and dihydroartemisinin plasma concentrations after the last dose administration were quantified using liquid chromatography coupled to tandem mass-spectroscopy. A simultaneous drug-metabolite population pharmacokinetic model for artemether and dihydroartemisinin was developed taking into account different disposition, absorption, error and covariate models. A separate modeling approach and a non-compartmental analysis (NCA) were also performed to enable a comparison with literature values and different modeling strategies.

Results

The treatment was well tolerated and there were no cases of recurrent malaria. A flexible absorption model with sequential zero-order and transit-compartment absorption followed by a simultaneous one-compartment disposition model for both artemether and dihydroartemisinin provided the best fit to the data. Artemether and dihydroartemisinin exposure was lower than that reported in non-pregnant populations. An approximately four-fold higher apparent volume of distribution for dihydroartemisinin was obtained by non-compartmental analysis and separate modeling compared to that from simultaneous modeling of the drug and metabolite. This highlights a potential pitfall when analyzing drug/metabolite data with traditional approaches.

Conclusion

The population pharmacokinetic properties of artemether and dihydroartemisinin, in pregnant women with uncomplicated P. falciparum malaria in Uganda, were described satisfactorily by a simultaneous drug-metabolite model without covariates. Concentrations of artemether and its metabolite dihydroartemisinin were relatively low in pregnancy compared to literature data. However, this should be interpreted with caution considered the limited literature available. Further studies in larger series are urgently needed for this vulnerable group.

Pharmacokinetic profiles of artesunate following multiple intravenous doses of 2, 4, and 8 mg/kg in healthy volunteers: phase 1b study

Background

Severe malaria results in over a million deaths every year, most of them in children aged less than five years and living in sub-Saharan Africa. Injectable artesunate (AS) was recommended as initial treatment for severe malaria by WHO in 2006. The Walter Reed Army Institute of Research (WRAIR) has been developing a novel good manufacturing practice (GMP) injection of AS, which was approved by the US FDA for investigational drug use and distribution by the CDC.

Methods

Tolerability and pharmacokinetics of current GMP intravenous AS, as an anti-malarial agent, were evaluated after ascending multiple doses of 2, 4, and 8 mg/kg daily for three days with 2-minute infusion in 24 healthy subjects (divided into three groups) in the Phase 1 clinical trial study.

Results

Results showed that there were no dose-dependent increases in any adverse events. Drug concentrations showed no accumulation and no decline of the drug during the three days of treatment. After intravenous injection, parent drug rapidly declined and was converted to dihydroartemisinin (DHA) with overall mean elimination half-lives ranging 0.15-0.23 hr for AS and 1.23-1.63 hr for DHA, but the peak concentration (C_max) of AS was much higher than that of DHA with a range of 3.08-3.78-folds. In addition, the AUC and C_max values of AS and DHA were increased proportionally to the AS climbing multiple doses.

Discussion

The safety of injectable AS, even at the highest dose of 8 mg/kg increases the probability of therapeutic success of the drug even in patients with large variability of parasitaemia.

Lopinavir/ritonavir significantly influences pharmacokinetic exposure of artemether/lumefantrine in HIV-infected Ugandan adults

Background

Treatment of HIV/malaria-coinfected patients with antiretroviral therapy (ART) and artemisinin-based combination therapy has potential for drug interactions. We investigated the pharmacokinetics of artemether, dihydroartemisinin and lumefantrine after administration of a single dose of 80/480 mg of artemether/lumefantrine to HIV-infected adults, taken with and without lopinavir/ritonavir.

Methods

A two-arm parallel study of 13 HIV-infected ART-naive adults and 16 HIV-infected adults stable on 400/100 mg of lopinavir/ritonavir plus two nucleoside reverse transcriptase inhibitors (ClinicalTrials.gov, NCT 00619944). Each participant received a single dose of 80/480 mg of artemether/lumefantrine under continuous cardiac function monitoring. Plasma concentrations of artemether, dihydroartemisinin and lumefantrine were measured.

Results

Co-administration of artemether/lumefantrine with lopinavir/ritonavir significantly reduced artemether maximum concentration (C_max) and area under the concentration–time curve (AUC) [median (range): 112 (20–362) versus 56 (17–236) ng/mL, P = 0.03; and 264 (92–1129) versus 151 (38–606) ng · h/mL, P < 0.01]. Dihydroartemisinin C_max and AUC were not affected [66 (10–111) versus 73 (31–224) ng/mL, P = 0.55; and 213 (68–343) versus 175 (118–262) ng · h/mL P = 0.27]. Lumefantrine C_max and AUC increased during co-administration [2532 (1071–5957) versus 7097 (2396–9462) ng/mL, P < 0.01; and 41 119 (12 850–125 200) versus 199 678 (71 205–251 015) ng · h/mL, P < 0.01].

Conclusions

Co-administration of artemether/lumefantrine with lopinavir/ritonavir significantly increases lumefantrine exposure, but decreases artemether exposure. Population pharmacokinetic and pharmacodynamic trials will be highly valuable in evaluating the clinical significance of this interaction and determining whether dosage modifications are indicated.

Orally formulated artemisinin in healthy fasting Vietnamese male subjects: a randomized, four-sequence, open-label, pharmacokinetic crossover study

Background

Artemisinin derivatives are used in antimalarial drug combination therapy. Artemisinin and piperaquine have recently been proven to be prospective candidates for combination therapy in the treatment of uncomplicated Plasmodium falciparum malaria.

Objective

The goal of this study was to evaluate the relative bioavailability and to characterize the pharmacokinetic properties of a new micronized powder formulation of artemisinin against the previous standard Vietnamese formulation when administered as a single oral dose or in combination with piperaquine.

Methods

This was a single-center, randomized, 4-sequence, open-label, crossover study conducted in 15 healthy male Vietnamese volunteers under fasting conditions with a washout period of 3 weeks between study visits. A single oral dose of 160 or 500 mg of artemisinin was administered alone or in combination with piperaquine. Potential adverse events were monitored daily by the clinician and by using laboratory test results. Frequent blood samples were drawn for 12 hours after dose. Artemisinin was quantified in plasma using LC-MS/MS. Pharmacokinetic parameters were computed from the plasma concentration–time profiles using a noncompartmental analysis method.

Results

Pharmacokinetic parameters T_max, C_max, AUC_0-∞, V_d/F, CL/F, and t_1/2 (mean [SD]) for the new formulation of artemisinin were 1.83 (0.88) hours, 178 (97) ng/mL, 504 (210) h × ng/mL, 1270 (780) L, 401 (260) L/h, and 2.21 (0.29) hours, respectively. The mean percentage of the test/reference formulation ratio for the logarithmically transformed values of C_max, AUC_0–last, and AUC_0–∞ were 121% (90% CI, 92.5–158), 122% (90% CI, 101–148), and 120% (90% CI, 98.0–146), respectively.

Conclusions

This single-dose study found that the dose-normalized C_max, AUC_0–last, and AUC_0–∞ mean geometric differences between the test and reference formulations were relatively small (<40%) and will probably not have a clinical impact in the treatment of malaria infections.

Interaction between artemether-lumefantrine and nevirapine-based antiretroviral therapy in HIV-1-infected patients

Artemether-lumefantrine and nevirapine-based antiretroviral therapy (ART) are the most commonly recommended first-line treatments for malaria and HIV, respectively, in Africa. Artemether, lumefantrine, and nevirapine are metabolized by the cytochrome P450 3A4 enzyme system, which nevirapine induces, creating potential for important drug interactions. In a parallel-design pharmacokinetic study, concentration-time profiles were obtained in two groups of HIV-infected patients: ART-naïve patients and those stable on nevirapine-based therapy. Both groups received the recommended artemether-lumefantrine dose. Patients were admitted for intense pharmacokinetic sampling (0 to 72 h) with outpatient sampling until 21 days. Concentrations of lumefantrine, artemether, dihydroartemisinin, and nevirapine were determined by validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. The primary outcome was observed day 7 lumefantrine concentrations, as these are associated with therapeutic response in malaria. We enrolled 36 patients (32 females). Median (range) day 7 lumefantrine concentrations were 622 ng/ml (185 to 2,040 ng/ml) and 336 ng/ml (29 to 934 ng/ml) in the nevirapine and ART-naïve groups, respectively (P = 0.0002). The median artemether area under the plasma concentration-time curve from 0 to 8 h [AUC((0-8 h))] (P < 0.0001) and dihydroartemisinin AUC((60-68 h)) (P = 0.01) were lower in the nevirapine group. Combined artemether and dihydroartemisinin exposure decreased over time only in the nevirapine group (geometric mean ratio [GMR], 0.76 [95% confidence interval {CI}, 0.65 to 0.90]; P < 0.0001) and increased with the weight-adjusted artemether dose (GMR, 2.12 [95% CI, 1.31 to 3.45]; P = 0.002). Adverse events were similar between groups, with no difference in electrocardiographic Fridericia corrected QT and P-R intervals at the expected time of maximum lumefantrine concentration (T(max)). Nevirapine-based ART decreased artemether and dihydroartemisinin AUCs but unexpectedly increased lumefantrine exposure. The mechanism of the lumefantrine interaction remains to be elucidated. Studies investigating the interaction of nevirapine and artemether-lumefantrine in HIV-infected patients with malaria are urgently needed.

Population pharmacokinetics of artemether, lumefantrine, and their respective metabolites in Papua New Guinean children with uncomplicated malaria

There are sparse published data relating to the pharmacokinetic properties of artemether, lumefantrine, and their active metabolites in children, especially desbutyl-lumefantrine. We studied 13 Papua New Guinean children aged 5 to 10 years with uncomplicated malaria who received the six recommended doses of artemether (1.7 mg/kg of body weight) plus lumefantrine (10 mg/kg), given with fat over 3 days. Intensive blood sampling was carried out over 42 days. Plasma artemether, dihydroartemisinin, lumefantrine, and desbutyl-lumefantrine were assayed using liquid chromatography-mass spectrometry or high-performance liquid chromatography. Multicompartmental pharmacokinetic models for a drug plus its metabolite were developed using a population approach that included plasma artemether and dihydroartemisinin concentrations below the limit of quantitation. Although artemether bioavailability was variable and its clearance increased by 67.8% with each dose, the median areas under the plasma concentration-time curve from 0 h to infinity (AUC(0-∞)s) for artemether and dihydroartemisinin (3,063 and 2,839 μg · h/liter, respectively) were similar to those reported previously in adults with malaria. For lumefantrine, the median AUC(0-∞) (459,980 μg · h/liter) was also similar to that in adults with malaria. These data support the higher dose recommended for children weighing 15 to 35 kg (35% higher than that for a 50-kg adult) but question the recommendation for a lower dose in children weighing 12.5 to 15 kg. The median desbutyl-lumefantrine/lumefantrine ratio in the children in our study was 1.13%, within the range reported for adults and higher at later time points because of the longer desbutyl-lumefantrine terminal elimination half-life. A combined desbutyl-lumefantrine and lumefantrine AUC(0-∞) weighted on in vitro antimalarial activity was inversely associated with recurrent parasitemia, suggesting that both the parent drug and the metabolite contribute to the treatment outcome of artemether-lumefantrine.

Bioequivalence of Two Intravenous Artesunate Products with Its Active Metabolite Following Single and Multiple Injections

In animal species and humans, artesunate (AS) undergoes extensive and complex biotransformation to an active metabolite, dihydroartemisinin (DHA). The bioequivalence of two intravenous AS pharmaceutical products with 5% NaHCO₃ (China Formulation) or 0.3 M PBS (WRAIR Formulation) was determined in rats in a two-formulation, two-period, and two-sequence crossover experimental design. Following single and multiple intravenous administrations, a series of blood samples was collected by using an automated blood sampler and drug concentrations were analyzed by LC-MS/MS. The 90% CI of the difference between the two intravenous formulations was contained within 80–125% of the geometric mean of pharmacokinetic parameters for AS and DHA in all animals dosed. Hematological effects were studied on days 1 and 3 after the final dosing, and a rapidly reversible hematological toxicity (significant reductions in reticulocyte levels) was seen in the peripheral blood of the rats treated with each formulation. The results showed that bioequivalence with the parent compound and active metabolite was fulfilled in the 82.3–117.7% ranges of all parameters (AUC_0−t, C_max, concentration average and degree of fluctuation) in the two-period and two-sequence crossover studies following single and repeated intravenous injections. For the metabolite, the equivalence was satisfied in most pharmacokinetic parameters tested due to the variability in the hydrolysis rate of AS to DHA. The WRAIR formulation of AS was considered to be bioequivalent to the Chinese formulation at steady-state according to the total drug exposure, in terms of both parent drug and active metabolite, rapidly reversal in reticulocyte decline, and extension of single and multiple administrations. Therefore, the parent drug and active metabolites should play similar important roles in the determination of efficacy and safety of the drug.

Pharmacokinetics of artemether and dihydroartemisinin in healthy Pakistani male volunteers treated with artemether-lumefantrine

Background

Artemether-lumefantrine is one of the most widely used anti-malarial drug combinations in the world with excellent tolerability and cure rates in adult and paediatric patients with uncomplicated falciparum malaria. The aim of this study was to evaluate the pharmacokinetics of artemether and its active metabolite, dihydroartemisinin, in healthy Pakistani volunteers.

Methods

Twelve healthy male Pakistani subjects, aged 20 to 50, were recruited into the study. A fixed oral combination of artemether-lumefantrine (80-480 mg) was given as a single oral dose. Frequent blood samples were collected and artemether and dihydroartemisinin were quantified in human plasma using solid-phase extraction and liquid chromatography coupled with tandem mass spectrometry. Drug concentration-time data were evaluated with non-compartmental analysis.

Results

Observed maximum concentrations (mean ± SD) of artemether and dihydroartemisinin were 184 ± 100 ng/mL and 126 ± 46 ng/mL, respectively. These concentrations were reached at 1.56 ± 0.68 hr and 1.69 ± 0.59 hr, respectively, after drug intake. The terminal elimination half-life of artemether and dihydroartemisinin were 2.00 ± 0.71 hr and 1.80 ± 0.31 hr, respectively. Apparent volume of distribution and oral clearance for artemether were estimated to 666 ± 220 L and 257 ± 140 L/hr. The same parameters were estimated to 702 ± 220 L and 269 ± 57 L/hr for dihydroartemisinin.

Conclusions

The overall pharmacokinetic properties of artemether and dihydroartemisinin in healthy Pakistani subjects are comparable to healthy subjects and patients from other populations.

Population pharmacokinetics and pharmacodynamics of artemether and lumefantrine during combination treatment in children with uncomplicated falciparum malaria in Tanzania

The combination of artemether (ARM) and lumefantrine is currently the first-line treatment of uncomplicated falciparum malaria in mainland Tanzania. While the exposure to lumefantrine has been associated with the probability of adequate clinical and parasitological cure, increasing exposure to artemether and the active metabolite dihydroartemisinin (DHA) has been shown to decrease the parasite clearance time. The aim of this analysis was to describe the pharmacokinetics and pharmacodynamics of artemether, dihydroartemisinin, and lumefantrine in African children with uncomplicated malaria. In addition to drug concentrations and parasitemias from 50 Tanzanian children with falciparum malaria, peripheral parasite densities from 11 asymptomatic children were included in the model of the parasite dynamics. The population pharmacokinetics and pharmacodynamics of artemether, dihydroartemisinin, and lumefantrine were modeled in NONMEM. The distribution of artemether was described by a two-compartment model with a rapid absorption and elimination through metabolism to dihydroartemisinin. Dihydroartemisinin concentrations were adequately illustrated by a one-compartment model. The pharmacokinetics of artemether was time dependent, with typical oral clearance increasing from 2.6 liters/h/kg on day 1 to 10 liters/h/kg on day 3. The pharmacokinetics of lumefantrine was sufficiently described by a one-compartment model with an absorption lag time. The typical value of oral clearance was estimated to 77 ml/h/kg. The proposed semimechanistic model of parasite dynamics, while a rough approximation of the complex interplay between malaria parasite and the human host, adequately described the early effect of ARM and DHA concentrations on the parasite density in malaria patients. However, the poor precision in some parameters illustrates the need for further data to support and refine this model.

Pharmacokinetics of dihydroartemisinin in Artekin tablets for single and repeated dosing in Chinese healthy volunteers

Aim. To study the pharmacokinetics of dihydroartemisinin (DHA) in Artekin (compound dihydroartemisinin) tablets in Chinese healthy volunteers. Methods. Eighteen healthy volunteers (9 males, 9 females) received Artekin tablets for oral administration. The plasma samples of DHA were analysed by liquid-liquid extraction and determined by HPLC/ESI/MS. Results. The plasma DHA concentration-time curves of single dose and repeated doses of DHA were fitted to a two-compartment open model. The mean pharmacokinetic parameters of DHA in a single dose were: t(1/2(beta))=1.245 +/- 0.495 h, C(max)=243.6 +/- 56.15 microg/l, AUC(0 --> infinity)=450 +/- 69 h x microg/l, V(d)=5.75 +/- 2.2 l/kg and Cl=3.245 +/- 0.38 l/h/kg, while in repeated doses they were: t(1/2(beta))=1.085 +/- 0.298 h, AUC(0 --> infinity)=444.35 +/- 80.43 h x ng/ml, V(d)=4.62 +/- 1.128 ml/kg, Cl=3.0125 +/- 0.875 ml/h/kg, respectively. Conclusion. The study showed that DHA in Artekin was rapidly absorbed, distributed and eliminated in the healthy subjects. The pharmacokinetic properties of DHA in Artekin were not affected by gender in a single dose. While in repeated doses accumulation of DHA did not appear after repeated doses.

First assessment in humans of the safety, tolerability, pharmacokinetics, and ex vivo pharmacodynamic antimalarial activity of the new artemisinin derivative artemisone

In preclinical studies, artemisone (BAY 44-9585), a new artemisinin derivative, was shown to possess enhanced efficacy over artesunate, and it does not possess the neurotoxicity characteristic of the current artemisinins. In a phase I program with double-blind, randomized, placebo-controlled, single and multiple ascending oral-dose studies, we evaluated the safety, tolerability, pharmacokinetics, and ex vivo pharmacodynamic antimalarial activity of artemisone. Single doses (10, 20, 30, 40, and 80 mg) and multiple doses (40 and 80 mg daily for 3 days) of artemisone were administered orally to healthy subjects. Plasma concentrations of artemisone and its metabolites were measured by liquid chromatography/tandem mass spectrometry (LC/MS-MS). Artemisone was well tolerated, with no serious adverse events and no clinically relevant changes in laboratory and vital parameters. The pharmacokinetics of artemisone over the 10- to 80-mg range demonstrated dose linearity. After the single 80-mg dose, artemisone had a geometric mean maximum concentration of 140.2 ng/ml (range, 86.6 to 391.0), a short elimination half-life (t(1/2)) of 2.79 h (range, 1.56 to 4.88), a high oral clearance of 284.1 liters/h (range, 106.7 to 546.7), and a large volume of distribution of 14.50 liters/kg (range, 3.21 to 51.58). Due to artemisone's short t(1/2), its pharmacokinetics were comparable after single and multiple dosing. Plasma samples taken after multiple dosing showed marked ex vivo pharmacodynamic antimalarial activities against two multidrug-resistant Plasmodium falciparum lines. Artemisone equivalent concentrations measured by bioassay revealed higher activity than artemisone measured by LC/MS-MS, confirming the presence of active metabolites. Comparable to those of other artemisinin's, artemisone's t(1/2) is well suited for artemisinin-based combination therapy for the treatment of P. falciparum malaria.

WITHDRAWN: Artemether-lumefantrine for treating uncomplicated falciparum malaria

BACKGROUND

Artemether-lumefantrine is being recommended by the World Health Organization for treating uncomplicated malaria. It is expensive. We sought evidence of its superiority over existing treatment regimens.

OBJECTIVES

To compare artemether-lumefantrine with other antimalarial drugs for treating uncomplicated falciparum malaria.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group specialized trials register (May 2005), CENTRAL (The Cochrane Library Issue 2, 2005), MEDLINE (1966 to May 2005), EMBASE (1988 to May 2005), conference proceedings, and reference lists of articles. We contacted experts in malaria research and the pharmaceutical company that manufactures artemether-lumefantrine.

SELECTION CRITERIA

Randomized and quasi-randomized trials comparing artemether-lumefantrine administered orally with standard treatment regimens (single drug or combination).

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied inclusion criteria to potentially relevant trials, assessed trial quality, and extracted data. Parasitaemia on day 28 (day 42 for sulfadoxine-pyrimethamine and day 63 for mefloquine) was the primary outcome. Adverse event information was collected from the studies.

MAIN RESULTS

Six trials (1698 participants) tested a four dose regimen. Failure rates for artemether-lumefantrine tended to be higher (comparisons included sulfadoxine-pyrimethamine, halofantrine, and mefloquine; difference statistically significant for mefloquine). When compared with chloroquine, artemether-lumefantrine was better in two studies, but the failure rate for chloroquine at these sites was over 50%. Two trials (419 participants) tested a six dose regimen against mefloquine plus artesunate. Artemether-lumefantrine was associated with higher failure rates but the studies were small.

AUTHORS' CONCLUSIONS

The four dose regimen of artemether-lumefantrine seems to be less effective than most other current antimalarial regimens. The six dose regimen is largely untested. The authors are aware that some recently published trials may change the results of this review, and are preparing an update. These trials are referenced in 'Studies awaiting assessment'.

Artemisinin antimalarials moderately affect cytochrome P450 enzyme activity in healthy subjects

The aim of this study was to investigate which principal human cytochrome P450 (CYP450) enzymes are affected by artemisinin and to what degree the artemisinin derivatives differ with respect to their respective induction and inhibition capacity. Seventy-five healthy adults were randomized to receive therapeutic oral doses of artemisinin, dihydroartemisinin, arteether, artemether or artesunate for 5 days (days 1-5). A six-drug cocktail consisting of caffeine, coumarin, mephenytoin, metoprolol, chlorzoxazone and midazolam was administered orally on days -6, 1, 5 and 10 to assess the activities of CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP2E1 and CYP3A, respectively. Four-hour plasma concentrations of parent drugs and corresponding metabolites and 7-hydroxycoumarin urine concentrations were quantified by liquid chromatography-tandem mass spectrometry. The 1-hydroxymidazolam/midazolam 4-h plasma concentration ratio (CYP3A) was increased on day 5 by artemisinin [2.66-fold (98.75% CI: 2.10-3.36)], artemether [1.54 (1.14-2.09)] and dihydroartemisinin [1.25 (1.06-1.47)] compared with day -6. The S-4'-hydroxymephenytoin/S-mephenytoin ratio (CYP2C19) was increased on day 5 by artemisinin [1.69 (1.47-1.94)] and arteether [1.33 (1.15-1.55)] compared with day -6. The paraxanthine/caffeine ratio (CYP1A2) was decreased on day 1 after administration of artemisinin [0.27 (0.18-0.39)], arteether [0.70 (0.55-0.89)] and dihydroartemisinin [0.73 (0.59-0.90)] compared with day -6. The alpha-hydroxymetoprolol/metoprolol ratio (CYP2D6) was lower on day 1 compared with day -6 in the artemisinin [0.82 (0.70-0.96)] and dihydroartemisinin [0.83 (0.71-0.96)] groups, respectively. In the artemisinin-treated subjects this decrease was followed by a 1.34-fold (1.14-1.58) increase from day 1 to day 5. These results show that intake of artemisinin antimalarials affect the activities of several principal human drug metabolizing CYP450 enzymes. Even though not significant in all treatment groups, changes in the individual metrics were of the same direction for all the artemisinin drugs, suggesting a class effect that needs to be considered in the development of new artemisinin derivatives and combination treatments of malaria.

Effect of artemether on pentobarbitone sleep and electrical activity in rats

Artemether (AM), a highly effective treatment for multidrug-resistant malaria and a component of artemisinin combination therapy, has been associated with some neurotoxicity following repeated high doses. This study was aimed at investigating the effect of AM on pentobarbitone sleep and electrical activities in rats. Wistar rats received AM i.p. at 3 dose levels: 1.5, 7.5, and 15 mg/kg, whereas control rats received 0.2 mL of the vehicle (3% v/v Tween 80). AM administered 20 min before pentobarbitone had no significant effect on the onset and duration of sleep. However, after a 7-day pretreatment, AM dose-dependently prolonged pentobarbitone sleep, as did chloramphenicol. Electroencephalogram and electromyogram recordings 20 min after pretreatment showed that AM (15 mg/kg) exhibited inhibitory activity similar to chlorpromazine as opposed to the excitatory effect of amphetamine. When pretreated for 7 days, rats receiving 1.5 mg/kg AM also showed inhibitory activity of the cortical centres, whereas desynchronization of the optic tectum and reticular formation was observed in rats pretreated with 7.5 and 15 mg/kg AM. The present data suggest that although the therapeutic equivalent dose of 1.5 mg/kg AM had no appreciable effects on pentobarbitone sleep but caused reduced electrical activity in rats, higher doses have more profound effects on both indices.

Supervised versus unsupervised antimalarial treatment with six-dose artemether-lumefantrine: pharmacokinetic and dosage-related findings from a clinical trial in Uganda

BACKGROUND

A six-dose antimalarial regimen of artemether-lumefantrine (A/L) may soon become one of the most widely used drug combination in Africa, despite possible constraints with adherence and poor absorption due to inadequate nutrition, and a lack of pharmacokinetic and effectiveness data.

METHODS

Within a trial of supervised versus unsupervised A/L treatment in a stable Ugandan Plasmodium falciparum transmission setting, plasma lumefantrine concentrations were measured in a subset of patients on day 3 (C [lum]day3) and day 7 (C [lum]day7) post-inclusion. Predictors of lumefantrine concentrations were analysed to show how both C [lum]day7 and the weight-adjusted lumefantrine dose affect 28-day recrudescence and re-infection risks. The implications of these novel findings are discussed in terms of the emergence of lumefantrine-resistant strains in Africa.

RESULTS

C [lum]day3 and C [lum]day7 distributions among 241 supervised and 238 unsupervised patients were positively skewed. Unsupervised treatment and decreasing weight-adjusted lumefantrine dose were negatively associated with C [lum]day3. Unsupervised treatment and decreasing age showed strong negative associations with C [lum]day7. Both models were poorly predictive (R-squared < 0.25). There were no recrudescences in either arm, but decreasing lumefantrine dose per Kg resulted in up to 13-fold higher adjusted risks of re-infection. Re-infections occurred only among patients with C [lum]day7 below 400 ng/mL (p < 0.001).

CONCLUSION

Maintaining the present six-dose regimen and ensuring high adherence and intake are essential to maximize the public health benefits of this valuable drug combination.

Artemether-lumefantrine (four-dose regimen) for treating uncomplicated falciparum malaria

BACKGROUND

The World Health Organization recommends artemether-lumefantrine, an expensive drug, as a treatment for uncomplicated malaria. We sought evidence of the superiority of the four-dose regimen over existing treatments.

OBJECTIVES

To evaluate the four-dose regimen of artemether-lumefantrine for treating uncomplicated falciparum malaria.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group Specialized Register (October 2005), CENTRAL (The Cochrane Library 2005, Issue 3), MEDLINE (1966 to October 2005), EMBASE (1988 to October 2005), LILACS (1982 to October 2005), conference proceedings, and reference lists of articles. We also contacted experts in malaria research and the pharmaceutical company that manufactures artemether-lumefantrine.

SELECTION CRITERIA

Randomized controlled trials comparing four doses of artemether-lumefantrine with standard treatment regimens (single drug or combination), or six doses of artemether-lumefantrine, for treating uncomplicated falciparum malaria.

DATA COLLECTION AND ANALYSIS

Two authors independently applied inclusion criteria to potentially relevant trials, assessed trial quality, and extracted data, including adverse events. Total failure by day 28 (day 42 for sulfadoxine-pyrimethamine and day 63 for mefloquine) was the primary outcome.

MAIN RESULTS

Seven trials (2057 participants) tested a four-dose regimen. More people tended to fail treatment with artemether-lumefantrine than with other drugs, including sulfadoxine-pyrimethamine (247 participants, 1 trial), halofantrine (86 participants, 1 trial), and mefloquine (233 participants, 1 trial; difference statistically significant for mefloquine). When compared with chloroquine, artemether-lumefantrine was better in two trials (378 participants), but over 50% of the participants treated with chloroquine had total failure by day 28. Fewer people failed treatment with the six-dose regimen compared to the four-dose regimen (RR 7.71, 95% CI 2.99 to 19.88; 306 participants, 1 trial).

AUTHORS' CONCLUSIONS

The four-dose regimen of artemether-lumefantrine seems to be less effective than regimens against which it has been tested. The six-dose regimen is superior to four-dose regimen.

Pharmacokinetics of dihydroartemisinin following oral artesunate treatment of pregnant women with acute uncomplicated falciparum malaria

OBJECTIVE

To determine the pharmacokinetic properties of dihydroartemisinin (DHA) following oral artesunate treatment in women with recrudescent multi-drug resistant falciparum malaria, in the second and third trimesters of pregnancy.

METHODS

Serial plasma concentrations of artesunate and DHA were measured in 24 women after the final dose of a 3 day treatment with artesunate (4 mg kg(-1) day(-1)) and atovaquone (20 mg kg(-1) day(-1)) plus proguanil (8 mg kg(-1) day(-1)), daily. Conventional non-compartmental modelling and a population one-compartment pharmacokinetic model were applied to the data.

RESULTS

Artesunate was very rapidly eliminated. For DHA the median [90% range] estimate of oral clearance (CI/F) was 4.0 [0.8-20.7] l hour(-1) kg(-1), total apparent volume of distribution (Vd/f) was 3.4 [0.9-60.7] l/kg, and terminal elimination half-life was 1.0 [0.6-2.4] h.

CONCLUSION

The kinetics of DHA are modified by pregnancy. The plasma levels of the active antimalarial metabolite DHA are lower than reported previously in non-pregnant adults. Dose-optimisation studies in pregnant women are needed.

Pharmacokinetics of the diastereomers of arteether, a potent antimalarial drug, in rats

The pharmacokinetics of alpha- and beta- diastereomers of arteether, a potent erythrocytic schizontocidal agent, and their active metabolite dihydroartemisinin were studied in male Sprague-Dawley rats after oral, intramuscular and intravenous administrations. Oral and intramuscular studies were carried out at three dose levels at 9, 17.5 and 30 mg kg(-1). The ratio of alpha- and beta-isomers was maintained at 30:70% w/w in the formulations used for the study. The average oral bioavailabilities of alpha-and beta-isomers, relative to intramuscular administration, were 9.6% and 3.8%, respectively, and the average in vivo alpha- to beta- ratio was 2.5. Following intravenous and intramuscular administrations the in vivo alpha- to beta- ratios were 0.7 and 0.9, respectively. The beta-isomer of arteether was characterized by a longer elimination half-life and a relatively larger volume of distribution than the alpha-isomer, suggesting that beta-arteether may be responsible for the prolonged in vivo schizontocidal activity. The alpha-isomer was absorbed rapidly after oral and intramuscular administrations and showed higher peak plasma concentrations but possessed a relatively shorter half-life. There was an apparent lack of linearity observed in terms of dose and AUCs for both alpha- and beta-arteether after oral and intramuscular administrations, suggesting nonlinear dose dependent pharmacokinetics at the dose levels studied. The rate and extent of conversion of arteether isomers to dihydroartemisinin was highest with oral and intravenous administration and least with intramuscular indicating that the intramuscular route of administration of the isomeric mixture may be more beneficial for malarial chemotherapy.

A semiphysiological pharmacokinetic model for artemisinin in healthy subjects incorporating autoinduction of metabolism and saturable first-pass hepatic extraction

AIMS

Previous studies have shown that the antimalarial drug artemisinin is a potent inducer of its own metabolism in both patients and healthy subjects. The aim of this study was to characterize the time-dependent pharmacokinetics of artemisinin in healthy subjects.

METHODS

Twenty-four healthy males were randomized to receive either a daily single dose of 500 mg oral artemisinin for 5 days, or single oral doses of 100/100/250/250/500 mg on each of the first 5 days. Two subjects from each group were administered a new dose of 500 mg on one of the following days after the beginning of the study: 7, 10, 13, 16, 20, or 24. Artemisinin concentrations in saliva samples collected on days 1, 3, 5, and on the final day were determined by HPLC. Data were analysed using a semiphysiological model incorporating (a) autoinduction of a precursor to the metabolizing enzymes, and (b) a two-compartment pharmacokinetic model with a separate hepatic compartment to mimic the processes of autoinduction and high hepatic extraction.

RESULTS

Artemisinin was found to induce its own metabolism with a mean induction time of 1.9 h, whereas the enzyme elimination half-life was estimated to 37.9 h. The hepatic extraction ratio of artemisinin was estimated to be 0.93, increasing to about 0.99 after autoinduction of metabolism. The model indicated that autoinduction mainly affected bioavailability, but not systemic clearance. Non-linear increases in AUC with dose were explained by saturable hepatic elimination affecting the first-pass extraction.

CONCLUSION

Artemisinin produces a rapid onset of enzyme induction, resulting in a decrease in its own bioavailability over time. The proposed model successfully described the time-course of the onset and normalization of the autoinduction of metabolism in healthy subjects receiving two different dosage regimens of the compound.

Artemisinins

Artemisinins were discovered to be highly effective antimalarial drugs shortly after the isolation of the parent artemisinin in 1971 in China. These compounds combine potent, rapid antimalarial activity with a wide therapeutic index and an absence of clinically important resistance. Artemisinin containing regimens meet the urgent need to find effective treatments for multidrug resistant malaria and have recently been advocated for widespread deployment. Comparative trials of artesunate and quinine for severe malaria are in progress to see if the persistently high mortality of this condition can be reduced.