A number of different drug trials were conducted worldwide to test the efficacy of artemether-lumefantrine. This combination treatment has proven highly efficacious in studies conducted in Ghana,19
or Papua New Guinea3
with > 97% PCR adjusted cure rates at Day 28. In contrast, we observed an unexpected high number of recurrent infections after treatment with Coartem in our longitudinal survey in children less than 5 years of age in Papua New Guinea. Treatment failures were confirmed by molecular typing of three different marker genes using a high-resolution technique with optimal discrimination power between genotypes. Using three different marker genes for discrimination of recrudescent from new infections provides confident identification of treatment failures.
Our study was not designed as a classic drug efficacy trial, but as a cohort study with longitudinal follow-up in 8-weekly intervals. This study design does not allow estimating in a standardized way the true rate of parasitological treatment failures, because recrudescent infections were only detected when the treated episode occurred within 28 or 42 days before a regular follow-up visit. If the interval between the episode and the next regular follow-up bleed was longer than 42 days, any recrudescent or newly occurring parasitemia remained undetected. Thus, with our study design we certainly underestimated the number of both, recrudescences and new infections. However, the specific advantage of our study consists in the fact that treatment success was viewed outside a clinical trial setting with outcomes reflecting the local situation in village health care. Our finding of a substantial number of recrudescences in non-trial conditions highlights potential problems of unsupervised Coartem usage.
In principle, several factors could have reduced the effectiveness of Coartem treatment in our study: 1) reduced sensitivity of parasites to Coartem, 2) host factors accounting for differences in metabolism of the drug, 3) inadequate adherence to treatment regimen, and 4) suboptimal absorption of drugs.
A reduced sensitivity to artemether-lumefantrine has been associated with an increased copy number of pfmdr1 in vitro
and in vivo
Similar findings of a reduced sensitivity to lumefantrine in vitro
were described by Lim and others,24
however, in that study the correlation could not be confirmed in vivo
. Recently, it has been shown that pfmdr1
gene amplifications were absent from different study sites in PNG, including an area adjacent to our study site.25
These results, together with the fact that an efficacy trial3
had confirmed Coartem to be highly effective in our study area indicate that reasons other than reduced drug sensitivity caused by an increase in pfmdr1
copy numbers are more likely to account for the high frequency of recrudescent infections.
Artemisinin derivatives are mainly metabolized by the human cytochrome P450 3A416
and also by the metabolic enzyme UDP-glucuronosyltransferase UGT2B7
The lumefantrine component of Coartem is also metabolized by CYP3A4
So far, functional significance of polymorphisms in CYP2B6
on the treatment outcome of artemisinin drugs is lacking. However, previous in vitro
studies have shown that these polymorphisms caused significant reduction in enzyme activity or expression,13,14
which generally elevated the plasma drug concentration of a antiretroviral drugs.13
It is likely that these polymorphisms act in a similar way on artemisinin plasma levels, and it has been proposed by Mehlotra and others,13,14
that the large inter-individual variability in the pharmacokinetics of artemisinin drugs, which has frequently been observed might partly be a result of a joint contribution of both polymorphisms in CYP2B6
. To exclude the possibility that host genetic factors account for the frequent treatment failures in our study population, polymorphisms in the human cytochrome 3A4, 2B6, and in UGT2B7
were studied. For the CYP2B6
, we only focused on the two polymorphisms CYP2B6
516G>T and UGT2B7
802C>T, which have been observed at high frequency in a previous study in PNG.13,14
We found mutant alleles in both, patients carrying new infections and in recrudescent infections, but treatment outcome and the presence of double mutants were not significantly associated. Thus, the double mutant CYP2B6
seems not to influence the outcome of Coartem treatment in this population. However, the trend toward increased proportion of double mutants in patients with treatment failures suggest that the correlation between treatment outcome and presence of double mutant should be further studied in a larger study population under standard drug trial conditions. The mutant allele CYP3A4
392A>G has previously been associated with a significant decrease in CYP3A4
and therefore leads to an increased exposure to lumefantrine. Our sequencing results did not reveal any polymorphisms at position 392. Homozygous carriers of the wild-type SNP were found in individuals harboring recrudescent or new infections. These results indicate that differences in metabolism of lumefantrine caused by mutations in CYP3A4
do not seem to account for the frequent treatment failures observed.
In most drug efficacy studies, treatment regimens are administered under supervision of a team nurse and therefore optimal compliance is mostly guaranteed or at least information on the adherence to the recommended treatment intervals or early interruption of treatment are available and can be accounted for in the analysis. In our study, treatment was mostly administered unsupervised. Parents were encouraged to complete all treatment doses, but in fact, no information is available from our study participants whether the complete treatment regimen was taken. Coartem rapidly alleviates malaria symptoms, which might frequently tempt patients to stop treatment earlier and keep the remaining tablets for a later malaria attack. Incomplete adherence to the full 6-dose regimen might have contributed to the observed frequency of treatment failures.
After initial reduction of the parasite biomass by the fast acting artemether, clearance of the residual parasites greatly depends on the longer lasting partner drug lumefantrine. Previous studies have shown that the plasma level of lumefantrine is a critical factor for treatment success.23,27
Food has a significant effect on the bioavailability of both components of the drug with an increased absorption when supplemented with fatty food.28
An increase in treatment success by 15% was observed in a study in Thailand when a fatty diet was co-administered with Coartem.29
In this study, parents or guardians of the study participants were advised to administer treatment with a fatty diet, however, no information is available to what extent these recommendations were followed. Inadequate plasma concentrations of lumefantrine might therefore have contributed to the high rate of treatment failures.
The high frequency of parasitological and clinical treatment failures in our study are contrary to findings from a recent drug efficacy trial, which was conducted in an area adjacent to our study site. In this previous study Coartem was reported to be highly efficacious in clearing P. falciparum
in children less than 5 years of age.3
An important difference between the two studies was that in the drug efficacy trial at least half of the doses were dispensed under supervision and supplemented with milk. This implies that incomplete adherence to the treatment regimen in combination with a lack of fatty diet might have contributed to the observed differences in treatment outcome. Furthermore, in our study Coartem was also given to P. falciparum
-infected children who presented with anemia (Hb < 7.5 g/dL), but did not show any other sign of symptoms. It is likely that these children were even less adherent to treatment, because they were without noticeable signs of disease. In the drug trial by Karunajeewa and others3
only microscopy positive recurrent infections were genotyped. In our analysis, all samples were genotyped regardless of microscopy results. Because sensitivity of PCR is considerably higher than that of microscopy, we most likely have detected recrudescences of low parasite density that would have remained undetected by microscopy. This might have further contributed to the higher treatment failure rate in our study.
Rather low levels of drug efficacy had also been reported from two studies in Ghana30,31
where PCR corrected cure rates at Day 28 were only 86.2% and 88.3%, respectively. In one of these studies only the first dose was given under supervision, whereas in the other study the administration of all 6 tablets was supervised. In both studies, no fatty diet was provided by the study team, but caretakers were encouraged to give fatty food at the time of drug administration. It was not checked by the study team whether these recommendations were followed. In a study in Uganda, no difference in treatment efficacy was observed between supervised and unsupervised administration of Coartem.32
In the latter study detailed explanations on intake of tablets and treatment schedule were provided to the patients. Such information may have resulted in adequate adherence. In a study conducted in Tanzania the issue of poor quality of malaria case management was demonstrated.33
Despite the high frequency of health facility attendance observed in this study, the proportion of patients receiving the appropriate antimalarial timely and correctly dosed was very low. Poor compliance to the prescribed treatment regimen leads to sub-curative doses and therefore does not only increase the rate of treatment failures, but also contributes to the emergence of antimalarial drug resistance.34
Adherence problems in home treatment could therefore lead to a situation similar to Cambodia, where a reduced in vivo
susceptibility of parasites to artemisinin has been reported.35,36
Further education on how, when, and where to treat febrile illness could therefore help to translate the high efficacy of new antimalarials such as ACT into effective community use and reduce the risk of emergence of resistance against these drugs. Recognizing the importance of good adherence to the Coartem treatment schedule, the PNG health authorities will provide extensive training to all health workers and conduct behavior change communication campaigns aimed at improving patient compliance as part of the upcoming introduction of Coartem as the national first-line treatment.
In summary, our observations highlight the importance of strict adherence to the complex dosing regimens of Coartem and the need to supplement the treatment with a fatty diet. The study by Kuranajeewa and others3
had shown that under optimal treatment conditions Coartem was highly effective in Papua New Guinea, whereas our results indicate that these high success rates might be difficult to achieve under routine clinical practice. Thus, it is of great importance that the introduction of Coartem as first-line treatment in PNG is accompanied by a provision of training and education for health workers to guarantee accurate treatment and compliance to the recommended guidelines. As pointed out by Piola and others,32
a great effort has to be made to convince patients and caretakers to complete the full 6-dose regimen despite the fast relief of symptoms.