Mefloquine was introduced first as a single-dose therapy for falciparum malaria in Thailand in 1984, but initial high cure rates were not sustained. In a proposition to halt the loss of anti-malarial monotherapies to resistance in rapid succession, the strategy of ACT with mefloquine was developed and was adopted in Thailand in 1994. The current regimen of a three-day combination of artesunate-mefloquine given in total adult dose of 600 mg (12 mg/kg body weight) artesunate and 1,250 mg (25 mg/kg body weight) mefloquine has been implemented by the Bureau of Vector Borne Disease, Department of Disease Control, Ministry of Public Health for the treatment of acute uncomplicated falciaprum malaria since 2008. The main objective was to obtain high cure rate of approaching 100% to prevent the spread of drug resistance. Prior to 2008, the same total dose of artesunate-mefloquine was given but as a shorter course of two days and two split doses of mefloquine (1,250 and 750 mg) given on the same day at 6-8 hours apart instead of two separate days as the current regimen. With the current regimen, in addition to the achievement of high cure rate, the incidence of vomiting due to high dose mefloquine and thus treatment failure is expected to be reduced. Absorption of mefloquine in malaria patients is dose limited and is reduced in the acute phase of illness. Splitting the dose of 25 mg/kg mefloquine improves mefloquine absorption and bioavailability, and thus and the therapeutic response in the treatment of acute falciparum malaria [16–18].
In the present study, a good initial response was observed in all patients where parasitaemia was cleared within three days after the initial dose of artesunate and mefloquine. The present combination regimen of artesunate-mefloquine was shown to improve the cure rate from approximately 87% with the 2 day course to 96.3% in the same study area (Tak province) during the year 2001 to 2002 . There were only two cases with treatment failure (cure rate 99.2%) on day 28, and 35 of treatment. It appears that the cure of this combination is still retained after eight years of its use (Ministry of publc Health, unpublished data). The concern about this three-day course is patient compliance when adopted as a public health policy. The aim of the present study was to assess the patient compliance of the current three-day course of artesunate-mefloquine when applied to field condition. As the combination is not a fixed dose regimen, assessment of blood concentration of only one combination partner, i.e. mefloquine with long half-life of 14-21 days  may not reflect the real full compliance of the combination regimen. Furthermore, since the half-lives of artesunate and its active plasma metabolite (dihydroartemisinin) are very short (0.5-2 hr), the drug would have been cleared from blood before 24 hours until patients returned for follow-up on the third day of treatment (day 3). Apart from mefloquine, plasma concentrations of primaquine on day 3 was, therefore, also used as a marker of patient's adherence to the three-day regimen with the assumption that if patients took primaquine tablets, it was likely that they would have also taken artesunate tablets on the second and third day. Several methods have been applied for monitoring of compliance to drug treatment particularly in the treatment of chronic diseases. These included clinical judgement of physician, patient self report, clinical response, biochemical measures, pill counts, pharmacy records, electronic medication monitoring devices and measuring of drug concentrations in blood or plasma [20–22]. Most methods except the last one suffer from their subjective evaluation. Measurement of anti-malarial drug concentrations in blood has been applied satisfactorily for monitoring of patient compliance to a 2 day combination regimen of artemether-mefloquine when adopted to field application . In another case, measurement of drug other than the anti-malarial itself, e.g. low dose phenobarbital, than the has been applied for monitoring compliance to short course treatment with anti-malarial regimens (5 day course of artesunate and 7 day course of the combination quinine-tetracycline) . The concentrations of artesunate and mefloquine on day 3 (about 24 hours after the last dose of mefloquine and primaquine on day 2) were selected as a time point for monioring the levels of both drugs. Mefloquine is a long half-life drug, therefore, whole blood mefloquine levels on day 3 after the initial treatment could be applied for monitoring of compliance to this combination regimen with good accuracy. Based on mefloquine and primaquine concentrations on day 3 after the intial treatment, patient compliance of as high as 96-98% was achieved when excluding the pharmacokinetic factor due to poor and variable drug absorption in some cases. It is noted however that patients realized that they were participating in a study and may significantly influenced their behaviour (i.e. better compliance). Using the questionnaire interview as a tool to evaluate compliance to the dose regimen, full compliance of 100% was obtained, which means that about 2-4% of non-compliance was undetected by this method. One case with undetectable mefloquine level on day 3 could be definitely classify as non-compliance. The low levels of mefloquine in the seven cases could be due either to non-compliance to the second dose of mefloquine or impaired drug absorption in each individual as none vomited within the first hour. In our previous study, patient compliance with a two-day course of artemether-mefloquine (an initial dose of 300 mg artemether on the first day, followed by 750 and 500 mg meflouine given on the second day at 4-6 hours apart) was investigated in the same area of the country. Median (range) whole blood mefloquine concentrations following the split doses were determined on the third day (1 day after the initial dose of mefloquine) was 2,262 (1,198-3,241) ng/ml. This is considered relatively low when compared with the concentrations observed after three days of an initial dose of mefloquine [median (range) of 2359 (27-10,965) ng/ml]. For primaquine on the other hand, plasma concentration on day 3 may not be absolutely a suitable marker for monitoring of compliance to this combination regimen in this field setting as the half-life of primaquine is relatively short (3.7-9.5 hr) . It has been reported that plasma concentration of primaquine at 25 hr after a single oral dose of primaqune is only approximately 10-15% of the Cmax . The case with undetectable primaquine concentration could be due to pharmacokinetic factors (impaired absorption and/or rapid clearance) and/or genuine non-compliance. Full compliance of approaching 100% with this short course regimen is considered excellent when comparing with compliance to long treatment courses of other regimens, such as a seven-day course of quinine-tetracycine, where prolonged drug administration or a relatively high incidence of cinchonism contributes to about 71.7% compliance in the field trials . This excellent compliance to the treatment regimen may also be due to reduced incidence of adverse effects from mefloquine with the split dose. A simple pre-packaging system and proper counselling could improve compliance with anti-malarial drug treatment [6, 26, 27]. Co-formulation of the drugs reduces the pill burden and more importantly, eliminates the possibility of patients taking only one component of the combination. In one study, pre-packaging anti-malarial drugs have been shown to improve compliance by approximately 20% in both adults and children . In addition, there were 50% reductions in cost of patients, waiting time at dispensaries and drug wastage at facilities. A new fixed-dose co-formulation of artesunate-mefloquine has been launched by Drugs for Neglected Diseases Initiative (DNDi), which decreases the risk of resistance due to compliance factor . Nevertheless, this strategy may have limitation with regard to practicality of dose adjustment.
It is interesting to note that 24.2 and 15.9% of patients had mefloquine and primaquine levels at baseline pretreatment. Seven% had baseline mefloquine concentrations less than 100 ng/ml, 11.6% had concentrations between 100 and 500 ng/ml, and 13% had concentrations greater than 500 ng/ml. This implies that patients may have received previous treatment with mefloquine longer than 35-48, between 35-48, and within 14 days, respectively . In one of our previous study, it was observed that 10.2, 11.5, 6.0 and 1.1% had baseline whole blood mefloquine concentrations of <100, 100-500, >500-1,000, and >1,000 ng/ml, respectlvely . The lower incidence of observed baseline primaquine level could be explained by the short half-life of primaquine . High incidence of baseline levels in this patient population indicates the high rate of malaria transmission in this area and/or drug resistance. Patients may have received treatment with artesunate-mefloquine treatment with or without primaquine (as a gametocytocide for falciparum malaria or as antirelapse for vivax malaria) from other health services nearby or from illegal anti-malarial drugs available in the markets for the current or previous malaria episode. There has been no data on the adherence to the 14-day course of primaquine for the treatment of vivax malaria, especially primaquine for the treatment of vivax malaria. There was no data on the adherence to the 14 day course of primaquine for the treatment of vivax malaria. Based on the prevalence of primaquine levels on admission of greater than 15%, and when considering the short half-life of this drug, this would suggest that some may have received previous treatment with primaquine within a day before participation in the study. This is of concern as accumulated high level of mefloquine may aggravate high incidence of adverse effects especially the serious neuropsychiatric effect. Based on patients' interview, none received previous treatment with any anti-malarial drug. Measurement of drug levels are, therefore, good confirmation of previous anti-malarial treatment.