Falciparum malaria in eastern Thailand: a randomized trial of the efficacy of a single dose of mefloquine.

Falciparum malaria in eastern Thailand: a randomized trial of the efficacy of a single dose of mefloquine A.L. Fontanet,1 B.D. Johnston,2 A.M. Walker,3 Y. Bergqvist,4 U. Hellgren,5 & W. Rooney6 Reported are the results of a randomized trial of a single dose of mefloquine (15 mg/kg or 25 mg/kg body weight) for the treatment of uncomplicated multidrug-resistant falciparum malaria. Of the 110 adult patients enrolled in the study 57 were randomly assigned to the 15 mg/kg group and 53 to the 25 mg/kg group. The baseline characteristics of the patients did not differ significantly in the two groups, except that those in the 15 mg/kg group had lower haemoglobin levels. Adverse effects following treatment were commoner in the 25 mg/kg group, but not significantly so. Seven patients (6%) did not complete the 42-day follow-up. The parasitological failure rates in the 15 and 25 mg/kg groups were, respectively, 50% (28/56) and 43% (23/53) on day 28, and 62% (33/53) and 56% (28/50) on day 42. Treatment failures were not correlated with the serum mefloquine concen- trations on day 2, and 13 out of 19 patients with serum mefloquine concentrations >2000 jg/I on day 2 showed an R response during the follow-up. The mean ratio between the concentrations of the (SR) -(-) and (RS)-(+) enantiomers of mefloquine on day 2 was 3.37, indicating that there are differences in their pharmacokinetics. Re-treatment of patients who showed an R response with seven days of quinine (30 mg.kg day-')+ tetracycline (25 mg.kg-1.day-1) was successful in 93% of the cases. Introduction Mefloquine has been used since 1984 to treat uncomplicated falciparum malaria in Thailand. To delay the development of mefloquine resistance in Plasmodium falciparum strains, mefloquine was at first given in a triple combination with sulfadoxine and pyrimethamine. At a dose of 15 mg per kg body weight, mefloquine produced cure rates close to 100% in field trials (1-4). However, because of the low susceptibility of P. falciparum strains to sulfa- doxine and pyrimethamine, treatment centres serving Khmer displaced persons along the eastem border of I Doctoral Student, Epidemiology Department, Harvard School of Public Health, 667 Huntington Avenue, Boston, MA, USA. Requests for reprints should be sent to Dr Fontanet at the follow- ing address: Epidemiological Research and Forecasting Unit, Global Programme on AIDS, World Health Organization, 1211 Geneva 27, Switzerland. 2 Registered Nurse, Thailand. 3 Professor, Epidemiology Department, Havard School of Public Health, Boston, MA, USA. 4Department of Clinical Chemistry, Falun Central Hospital, Falun, Sweden. 5 Department of Infectious Diseases, Huddinge University Hos- pital, Karolinska Institute, Huddinge, Sweden. 6 WHO Laboratory Specialist, Bangkok, Thailand. Reprint No. 5453 Thailand changed in July 1990 from the triple com- bination to mefloquine alone. A year later, an in vivo test of mefloquine efficacy in a Khmer displaced persons camp reported a cure rate of only 41% (5). Since it had been reported in an area adjacent to the Cambodian border that patients who received 25 mg of mefloquine per kg body weight had a higher maximum plasma mefloquine concentration than patients treated with 15 mg/kg (6), we initiated a clinical trial to compare the in vivo outcomes of patients treated with a single dose of 15 mg/kg or 25 mg/kg of mefloquine. Patients and methods Study site The study was carried out in Site 8, a Khmer dis- placed persons camp on the border between Thai- land and Cambodia. The camp had a population of 45 000, 40% of whom were children under the age of 10 years; it was also used as a referral hospital for patients from Cambodia. Malaria is the leading cause of morbidity and mortality in the camp, according to data from the outpatient department and the hospital. The monthly malaria incidence typically varies be- tween 50 and 2000 cases, depending on the season. Most cases are due to P. falciparum (90%), the Bulletin of the World Health Organization, 1994, 72 (1): 73-78 © World Health Organization 1994 73 A.L. Fontanet et al. remainder being P. vivax infections. Uncomplicated falciparum malaria cases are treated with 15 mg/kg body weight of mefloquine (Lariam, Roche) in a single dose. Severe cases are treated with intra- veneous quinine for up to 7 days, which is replaced by orally administered quinine and tetracycline when the patient is able to swallow tablets. Mosquito collections made over the period 1983-85 show that areas close to the camp were heavily infested with both of the region's malaria vectors, Anopheles dirus and A. minimus. Study procedure Between September and November 1991, patients diagnosed with uncomplicated falciparum malaria at the outpatient department were treated with the camp's usual regimen of a single dose of 15 mg/kg of mefloquine. The following were contraindications for mefloquine treatment: cerebral symptoms, haemo- globin level <7 g/dl, high parasitaemia, and pregnancy. Immediately after this first dose, adults with no history of treatment with quinine or mefloquine dur- ing the previous month were recruited for the study if they were willing to be randomized to receive a further dose of 10 mg/kg of mefloquine and if they were willing to remain available for follow-up for 42 days. The informed consent to participate in the study was obtained from the patients through the help of a translator, and the dose of 10 mg/kg of mefloquine was given to patients chosen using a table of random numbers. The interval between the first and the second dose never exceeded 15 minutes. Routine clinical information was collected using a standard form while the patients remained under observation for one hour after treatment in order to record whether or not they vomited within this period. All thick smears were subsequently reviewed by an expert microscopist from the Thai Malaria Divi- sion. The number of parasites was calculated against 100 leukocytes (assuming a leukocyte count of 8.0 x 109 per litre). Patients were retained for the study if they had >1600 asexual forms of P. falciparum per gl of blood and no mixed P. falciparumIP. vivax infections. Patients were asked to return to the outpatient department for a thick smear on days 2, 7, 14, 21, 28, 42 and if they experienced any fever or symptoms of malaria outside the regular days of follow-up. Treatment responses were categorized as RI, RII, RIII, or sensitive, using a modification of the WHO classification scheme (7). (RI was assigned to all patients who had a negative slide on day 7 but whose slide became positive for asexual forms of P. falciparum between day 8 and day 42; RII, to patients whose parasitaemia on day 2 had decreased by .75% of the level on day 0, and whose slides were still positive for asexual forms of P. falciparum on day 7; RIII, to patients whose parasitaemia on day 2 had decreased by <75% of that on day 0; and sen- sitive, to patients who remained free of parasitaemia after day 6. An "R" response is used later in this arti- cle to indicate either RI, RII, or RIII. All R responses were treated orally for 7 days with quinine (30 mg per kg per day) + tetracycline (25 mg per kg per day) in hospital. A final thick smear was taken 14 days after the first day of quinine treatment to confirm the cure. After their further consent had been obtained, 29 patients were randomly selected and 5 ml of venous blood was collected from each of them on day 2 in order to determine their serum mefloquine concen- tration. Serum was separated from blood by centrifu- gation, kept on ice, and stored at <4 °C. The centrifu- gation was performed by hand and separation of serum may therefore may have been incomplete for some blood samples. Mefloquine and its carboxylic metabolite in the serum sample were assayed using high-performance liquid chromatography (HPLC) (8) and the (SR)-(-) and (RS)-(+) enantiomers of meflo- quine by an enantioselective HPLC method using a chiral counter-ion (9). The lower limit of determina- tion was 50 jg/l for mefloquine and its carboxylic metabolite and 125 jg/l for the individual enantiomers. The study design was approved by the ethics committee of the United Nations Border Relief Operations (UNBRO). Statistical analysis. Differences in proportions were analysed using X2 and Fisher's exact tests. Means were compared using Student's t-test. Results Patients' characteristics at baseline A total of 110 patients were enrolled in the study from November to December 1991: 57 received 15 mg/kg body weight of mefloquine and 53 received 25 mg/kg. The patients' baseline characteristics are summarized in Table 1. There were no significant differences between the two groups, except for the mean haemoglobin level, which was lower for the 15 mg/kg group (9.4 g/dl versus 10.0 g/dl, P=0.03). Adverse effects of the treatment Of the 57 patients in the 15 mg/kg group, four (7%) vomited within one hour of receiving mefloquine, 11 (19%) reported diarrhoea in the first two days after treatment, and 40 (70%) complained of dizziness on day 2; among the 53 patients in the 25 mg/kg group, the corresponding numbers were 7 (13%), 14 (26%), WHO Bulletin OMS. Vol 72 199474 Efficacy of mefloquine in eastern Thailand Table 1: Baseline characteristics of the 110 study patients Mefloquine dose (mg/kg body weight) 15 25 No. of patients 57 53 No. of males 49 (86)a 43 (81) Mean age ± SD (years) 31.8 ± 11.0 34.7 ± 12.3 No. of reported 0 30 (53) 24 (45) mefloquine treatments 1-2 15 (26) 22 (42) in past year 23 12 (21) 7 (13) History of vomiting or 13 (23) 16 (30) diarrhoea prior to treatment Mean haemoglobin level ± SD 9.4 ± 1.2 10.0 ± 1.5b (g/dl) Geometric mean parasitaemia 25 600 34 900 (per ,i) a Figures in parentheses are percentages. b P<O.05, Student's t-test. and 39 (74%). None of these differences was statisti- cally significant. Patients who complained of diges- tive disorders at the initial examination were more likely to report a history of diarrhoea during the first two days after treatment (P = 0.02). Two patients in the 25 mg/kg group who vomit- ed within one hour of receiving their dose were re- treated because it appeared that the drug had been regurgitated in the vomitus. Mefloquine failure Of the 110 patients, seven (6%) did not complete the follow-up: four in the 15 mg/kg group (one lost to follow-up on day 15 and three on day 29); and three in the 25 mg/kg group (all lost to follow-up on day 29). The parasitological failure rates on day 28 and day 42 for the two treatment groups are shown in Table 2. The proportion of RIII patients was lower in the 25 mg/kg group, but there was no overall impact of dose on the treatment failure rates. A total of 50 of the 61 patients with an R response agreed to be treated orally for 7 days in hospital with quinine (30 mg.kg-'.day-1) + tetracy- cline (25 mg.kg-'.day-'). Of these patients, 45 retumed for a control thick smear 14 days after the initiation of the quinine-tetracycline treatment: 42 (93%) patients had a negative smear; one had a posi- tive smear on day 14, but a negative smear on day 16 and was then not re-treated; and the other two patients who were positive on day 14 were re-treated with quinine-tetracycline, an initial course of qui- nine being given intravenously. Serum mefloquine concentrations A total of 29 patients, (16 in the 15 mg/kg group and 13 in the 25 mg/kg group) agreed to have samples of blood drawn on day 2 for measurement of the serum mefloquine concentration. The mean serum meflo- quine concentration was almost identical in the two groups (2165 ,ug/l in the 15 mg/kg group versus 2284 jl in the 25 mg/kg group; P = 0.69). The stan- dard deviation (SD) of the serum mefloquine con- centration was considerably greater for the 25 mg/ kg group (995 jg/l versus 602 jg/l). The mean ± SD serum concentration on day 2 for the mefloquine en- antiomers was 1689 ± 578 jg/l for (SR)-(-) and 535 ± 220 jg/l for (RS)-(+). The serum concentrations of the (SR)-(-) and (RS)-(+) enantiomers were strong- ly correlated with the total serum mefloquine con- centrations (r = 0.99 and 0.92 resp.). The mean ratio of the concentrations of the (SR)-(-) and (RS)-(+) en- antiomers on day 2 was 3.37. Patients who vomited within an hour of treat- ment had significantly lower serum mefloquine con- centrations on day 2 than those who did not (mean: 1289 ,ug/l versus 2300 ,ug/l; P = 0.03). Serum meflo- quine levels were the same for the seven patients who had a history of diarrhoea during the first two days after treatment as those who did not (mean: 2073 jg/l versus 2264 jg/l; P = 0.58). Patients who complained of dizziness on day 2 had a higher serum mefloquine concentration than those who did not (mean: 2394 jug/l versus 1371 jig/l; P = 0.006). There was no correlation between the in vivo outcome and the serum mefloquine concentration on day 2: patients who showed an R response had a mean serum concentration of 2344 jig/l compared with 2012 ,ug/l for patients who were successfully treated (P = 0.33). It should be noted that 13 of the 19 patients whose serum mefloquine concentration was >2000 jig/l on day 2 exhibited an R response. Patients with RII and RIII responses had lower Table 2: Mefloquine response rate in the two treatment groups Day of follow-up: 28 42 Mefloquine dose Mefloquine dose (mg/kg body weight) (mg/kg body weight) 15 25 15 25 No. of patients 56 53 53 50 % of patients who were: RI 23 20 35 33 Rhl 11 19 11 19 Rill 16 4 16 4 Sensitive 50 57 38 44 WHO Bulletin OMS. Vol 72 1994 75 A.L. Fontanet et al. serum mefloquine concentrations (than patients with RI or sensitive responses (mean: 2023 gg/l versus 2666 gg/l; P = 0.09). Discussion Recent studies conducted along the Thailand-Myan- mar (10) and Thailand-Cambodia (5) borders have shown that treatment of P. falciparum infections with mefloquine dosages of 15 mg/kg are associated with disturbingly high failure rates. Our results confirm these findings, with a failure rate of 62% on day 42 for the group that received 15 mg/kg-very similar to the 59% failure rate that we have previous- ly reported for this area among patients who received this dose of mefloquine (5). We cannot exclude the reinfection of some patients, but the early treatment failures, i.e., the RII and RIII responses (which can- not be reinfections), accounted for a large proportion of all failures. A single dose of 25 mg/kg of mefloquine did not improve the outcome: the 56% failure rate observed is close to the 62% found with the 15 mg/kg dose. This may be partly explained by the low mefloquine susceptibility of P. falciparum strains in this area: 13 patients with serum mefloquine concentrations >2000 jg/l on day 2, which used to be associated with successful treatment (6), exhibited an R response during the follow-up. With such highly mefloquine-resistant P. falciparum strains, an increase in the treatment dose was insufficient to achieve in vivo parasiticidal drug concentrations. In addition, mefloquine absorption seems to be erratic in adults at a single dose of 25 mg/kg, as shown by the large variation in the serum concentrations on day 2. The results of a similar study that compared 15 mg/kg and 25 mg/kg of mefloquine for the treatment of uncomplicated falciparum malaria on the Thai- land-Myanmar border, where drug resistance to mef- loquine has previously been documented (10), have recently appeared (11). In contrast with our findings, the higher dose of mefloquine was accompanied by a reduced risk of treatment failure: 40% of the patients treated with 15 mg/kg experienced a treatment fail- ure by day 28, compared with only 9% of those treated with 25 mg/kg. It should be noted that the 25 mg/kg treatment was given in two doses separated by a 12-24-hour interval. These results are encourag- ing, but may have arisen because of the lower level of drug resistance of the P. falciparum strains on the Thailand-Myanmar border: the risk of treatment fail- ure on days 7-9 was only 7% and 1% for the 15 mg/kg and 25 mg/kg regimen, respectively, com- pared with 27% and 23%, respectively, in our study. Mefloquine consists of a racemic mixture of the (SR)-(-) and (RS)-(+) enantiomers. Both enantiomers have the same effect against P. berghii in mice (12), and against a chloroquine-resistant P. falciparum strain in vitro (13). The (RS)-(+) enantiomer may be of particular interest since its biological half-life seems to be shorter (14) and its acetylcholinesterase and butyrylcholinesterase inhibitor activity may be lower (15). One consequence of its shorter half-life is that the selection pressure for drug-resistant strains of the malaria parasite could be lower in users of the pure (RS)-(+) enantiomer. The reduced esterase in- hibitor activity might also lead to a lower frequen- cy of adverse drug reactions among these users com- pared with users of the racemic mixture. The serum concentrations of the (RS)-(+) enantiomer were low- er than those of the the (SR)-(-) enantiomer in our study, a finding consistent with the results report- ed by Eggelte et al. (14) and Gimenez et al. (16). The very strong correlation between the serum enantio- mer concentration and the total serum mefloquine concentration precluded differentiation between ad- verse reactions specific to either enantiomer and those associated with total mefloquine. Adverse effects were more frequent with the 25 mg/kg single dose of mefloquine, but did not signifi- cantly differ from what was observed with the 15 mg/kg dose. The correlation between early vomiting within an hour of receiving mefloquine and a reduc- tion in the concentration of mefloquine on day 2 is similar to the findings reported by Karbwang et al. (17). This underlines the need to re-treat patients who exhibit early vomiting. Patients with late vomit- ing should, however, not be re-treated since this might be due to high ("toxic") concentrations of mefloquine, as demonstrated for Tanzanian children (18). It is of interest to note that the occurrence of dizziness on day 2 was strongly associated with higher serum concentrations of mefloquine. Re-treatment with quinine-tetracycline was suc- cessful in 93% of instances. Acknowledgements We thank the Khmer staff working in Site 8 camp's hospi- tal for participating in the study; Mr K. Kawpasit, Thai Malaria Division, for analysing the microscope slides; the staff of the Christian Alliance Mission (CAMA) for their assistance in managing the patients; and the United Nations Border Relief Operations for their technical assis- tance. The study was supported by grants from the Pharma- coepidemiology Training and Research Fund (Epidemiol- ogy Department, Harvard School of Public Health, Boston, MA, USA), and from the Julian Mack Funds (International Health Department, Harvard School of Public Health, Bos- ton, MA, USA). Arnaud Fontanet is a recipient of a Lavoisier, a Fondation M6rieux, and a Foundation Philippe scholarship. Barbara Johnston is a recipient of a Rotary scholarship. WHO Bulletin OMS. Vol 72 199476 Efflcacy of mefloquine in eastern Thailand Resume Paludisme A falciparum dans l'est de la Thailande: essai randomis6 sur 1'efficacit6 d'une dose unique de m6floquine Cet article presente les resultats d'un essai rando- mise portant sur I'administration d'une dose unique de mefloquine (15 mg/kg ou 25 mg/kg de poids corporel) pour le traitement du paludisme a falci- parum polypharmacor6sistant non compliqu6. Au total, 110 sujets adultes ont e recrutes dans l'6tude et repartis par tirage au sort dans des groupes recevant 15 mg/kg de m6floquine (57 sujets) ou 25 mg/kg (53 sujets). Les donnees de r6ference des patients ne diff6raient pas sensible- ment entre les deux groupes, si l'on excepte une h6moglobinemie plus faible dans le groupe a 15 mg/kg. Dans ce dernier groupe, 4 patients (7%) ont vomi dans l'heure suivant le traitement, 11 (19%) ont signale avoir eu une diarrh6e au cours des deux jours suivants, et 40 (70%) ont souffert de vertiges le jour 2. Dans le groupe a 25 mg/kg, les nombres correspondants de patients 6taient 7 (13%), 14 (26%) et 39 (74%). Aucune de ces dif- f6rences n'etait statistiquement significative. Au total, 7 patients (6%) (4 dans le groupe a 15 mg/kg et 3 dans le groupe a 25 mg/kg) n'ont pu etre suivis pendant les 42 jours de 1'etude. Les taux d'6chec parasitologique dans les groupes a 15 mg/kg et 25 mg/kg 6taient respectivement de 50% (28/56) et 43% (23/53) le jour 28, et 62% (33/53) et 56% (28/50) le jour 42. II n'y avait pas de correlation entre les echecs du traitement et les taux seriques de m6floquine le jour 2, puisque 13 sujets, sur les 19 ayant un taux de mefloquine serique sup6rieur a 2000,g/l le jour 2 ont presen- t6 une r6ponse de type R au cours de la periode de suivi. Le rapport moyen entre les concentra- tions des 6nantiomeres (SR)-(-) et (RS)-(+) de m6floquine le jour 2 6tait de 3,37, ce qui montre qu'il existe des diff6rences de pharmacocin6tique entre ces deux formes. Chez les sujets ayant pr6sente une reponse de type R, un nouveau traitement de sept jours par la quinine (30 mg/kg par jour) plus tetracycline (25 mg/kg par jour) a conduit a la gu6rison dans 93% des cas. References 1. Doberstyn EB et al. Single dose therapy of falcipa- rum malaria with mefloquine or pyrimethamine-sul- fadoxine. Bulletin of the World Health Organization, 1979, 57: 275-279. 2. Harinasuta T et al. Phase II clinical trial of meflo- quine in patients with chloroquine-resistant falcipar- um malaria in Thailand. Bulletin of the World Health Organization, 1983, 61: 299-305. 3. Meek SR et al. Treatment of falciparum malaria with quinine and tetracycline or combined meflo- quine-sulfadoxine-pyrimethamine on the Thai-Kam- puchean border. 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Journal of chromatography, 1988, 432: 253-263. 9. Bergqvist Y et al. Enantioselective HPLC determi- nation of (SR)- and (RS)-mefloquine in plasma using N-benzyloxycarbonyl-glycyl-L-proline as chiral counter ion. Journal of chromatography, (in press). 10. Nosten F et al. Mefloquine-resistant falciparum malaria on the Thai-Burmese border. Lancet, 1991, 337: 1140-1143. 11. Ter Kuile FO et al. High-dose mefloquine in the treatment of multidrug resistant falciparum malaria. Journal of infectious diseases, 1992, 166: 1393- 1400. 12. Carroll Fl et al. Optical isomers of aryl-2-piperidyl- methanol antimalarial agents: preparation, optical purity, and absolute stereochemistry. Journal of medicinal chemistry, 1974, 17: 210-219. 13. Basco LK et al. Absence of antimalarial activity or interaction with mefloquine enantiomers in vitro of the main human metabolite of mefloquine. Transac- tions of the Royal Society of Tropical Medicine and Hygiene, 1991, 85: 208-209. 14. Eggelte TA et al. Enantiomer-specific monoclonal antibodies against mefloquine. XIII International Congress for Tropical Medicine and Malaria, Chol- buri, Thailand, 29 November to 4 December 1992 (Abstract ThO8-4), 1992. 15. Ngiam TL et al. Stereospecific inhibition of cho- linesterases by mefloquine enantiomers. Chemical and pharmaceutical bulletin, 1987, 35: 409-412. 16. Gimenez F et al. Determination of the enantiomers of mefloquine in plasma and whole blood using a coupled achiral-chiral, high-performance liquid chro- matographic system. Journal of chromatography, 1990, 529: 339-346. 17. Karbwang J et al. Pharmacokinetics and pharma- codynamics of mefloquine in Thai patients with WHO Bulletin OMS. Vol 72 1994 77 A.L. Fontanet et al. acute falciparum malaria. Bulletin of the World Health Organization, 1991, 69: 207-212. 18. Hellgren U et al. Standard and reduced doses of mefloquine for treatment of Plasmodium falciparum in Tanzania: whole blood concentrations in relation to adverse reactions, in vivo response, and in vitro susceptibility. American journal of tropical medicine and hygiene, 1991, 45: 254-262. 78 WHO Bulletin OMS. Vol 72 1994