Prospective double-blind trial of two different doses of mefloquine plus pyrimethamine—sulfadoxine compared with pyrimethamine—sulfadoxine alone in the treatment of falciparum malaria

Bulletin ofthe WorldHealth Organization, 63 (4): 731-737 (1985) © World Health Organization 1985 Prospective double-blind trial of two different doses of mefloquine plus pyrimethamine-sulfadoxine compared with pyrimethamine-sulfadoxine alone in the treatment of falciparum malaria D. BOTERO M. RESTREPO,2 & A. MONTOYA2 This double-blind study is based on the treatment of 75 adult male patients suffering from Plasmodium falciparum malaria in Medellin, Colombia, a city in which there is no malaria transmission. The patients, who came from regions with high resistance to antimalarials, were divided into three groups receiving single-dose treatment asfollows: a combination of 280 mg mefloquine, 800 mg sulfadoxine and 40 mg pyrimethamine; a combination of420 mg mefloquine, 1200 mg sulfadoxine and 60 mgpyrimethamine; and a combination of1500mg sulfadoxineand 75 mgpyrimethamine. After treatment, follow-up examination wasperformed dailyfor! week and then weeklyfor another3 weeks. The cure rate in the mefloquine groups (within the study period of 28 days) was 100%, and in the third group 75%o. Normal blood levels ofthe administered drugs werefound in 6patients of the third group who were not cured; they were subsequently cured with a single dose of 1000 mg ofmefloquine. Drug tolerance was good and no toxic effects were demonstrated in blood and urine examinations. While the doses in the drug combinations (containing mefloquine) gave very good results, we would recommend a slightly higher dose combination of mefloquine with sulfadoxine-pyrimethamine for the treatment of fakciparum malaria in areas with a high prevalence of chloroquine resistance. Owing to a variety of factors, malaria is at present a resurgent disease. The number of cases per year has been estimated at over 300 million, and in Africa alone it is thought to be the cause of death of more than 1 million people every year. One of the many problems involved with malaria is the widespread resistance of Plasmodium falciparum to antimalarial drugs (1). Although the chemotherapy of malaria is the subject of many papers and other publications, practising physicians in the tropics may find them hard to obtain. Those with this difficulty should try to consult the recent WHO monograph on thesubject (2). Chloroquine resistance in P.falciparum malaria was well documented for the first time in 1961 in two patients from the Magdalena valley in the north- eastern part of Colombia (3). The strain isolated from ' Professor of Parasitology, Faculty of Medicine, University of Antioquia, P.O. Box 1226, Medellin, Colombia. Requests for reprints should be sent to this author. 2 State Health Central Laboratory and Corporation for Biological Investigations, Medellin, Colombia. one of these patients was resistant to this drug in experimentally induced malaria in humans (4). Several years later this resistance was also found in cases from the country's Pacific coast (5), and has recently been confirmed both in vitro and in vivo in a larger number of cases from different parts of Colombia (6,7). In 1973 a review of the geographical distribution of resistance to 4-aminoquinolines cited other countries in Central and South America as well as parts of south-east Asia (8). Resistance of P.falciparum to combined pyri- methamine-sulfadoxine was initially seen in just a few cases in a study of experimentally induced malaria in Brazil (9). Recent publications from that country have shown that, in cases from the Amazon region, resistance to pyrimethamine-sulfadoxine was as high as 630/ (10, 11). Similar findings were also reported from south-east Asia (12) and many other countries, including Colombia (13). Resistance to chloroquine and pyrimethamine-sulfadoxine has also been described in Africa (14) and in Papua New Guinea (15). 4577 -731 D. BOTERO ET AL. The widespread and increasing resistance of P.falciparum to these drugs has necessitated the development of new antimalarials and more effective drug combinations. As a result, mefloquine or quinolinemethanol hydrochloride, which is related to quinine, was developed by the US Army Antimalarial Drug Program after screening more than 250 000 possible drugs (16). With a mean half-life in the bloodstream of 21 days, mefloquine is active against multidrug-resistant strains of P.falciparum in single oral doses. Since the initial phase I tolerance experiments reported in 1975, clinical studies have shown that this drug is well tolerated when taken orally, has a high radical cure rate in P.falciparum infections, and displays dramatic suppressive (prophylactic) activity against this species and also against P. vivax (17). The combination of mefloquine with pyri- methamine-sulfadoxine shows an additive blood schizontocidal action and the development of resistance was greatly delayed when tested in Plasmodium berghei (18). These findings support the interest in clinical trials using these drugs for the treatment of P.falciparum malaria. The tablet used in our study contained 140 mg mefloquine (base), 400 mg sulfadoxine and 20 mg pyrimethamine. This is different from the formulation currently being developed by Hoffmann-La Roche in collaboration with WHO, which contains 250 mg mefloquine (base), 500 mg sulfadoxine and 25 mg pyrimethamine. The latter formulation was agreed upon following discussions between the company and WHO because it was considered that, with the lower- dose combination, a fully curative effect might not be obtained. MATERIALS AND METHODS This study was carried out from April 1982 to February 1983 on 75 patients who had been infected with P.falciparum malaria in regions where chloroquine-resistant strains were prevalent. These patients were treated and followed up for 1 month in the city of Medellin where natural transmission of malaria does not occur. The criteria for the selection of patients were: males over 14 years of age, P.falciparum parasitaemia of more than 400 trophozoites per mm3 with symptomatic disease, and no previous treatment with other antimalarials during the 4 weeks prior to entering the trial. All patients had a negative Dill-Glazko test for chloroquine in the urine. The patients were seen daily during the first week following treatment and then weekly for 3 weeks, except for 7 cases who were followed up for a period of 1-3 weeks, 3 cases for 2 weeks, and 2 cases for 1 week; only one patient dropped out. Age, weight, height, past history of allergic reac- tions and concomitant associated illnesses, if present, were recorded for each patient at the initial examination. All patients gave their verbal consent to be included in the study. The following clinical parameters were assessed before treatment and on each visit: body temperature, blood pressure, pulse rate, spleen palpation, liver palpation, and signs and symptoms that could be attributed to malaria, such as headache, vomiting and diarrhoea. The state of consciousness, presence or absence of chills, and complications as well as any adverse reactions occurring during the study were recorded, indicating the type, severity, date of onset and duration of the reaction. Any concomitant medication with other drugs was also recorded. The following laboratory parameters were assessed before and after treatment: Hb level, RBC count, ESR, erythrocyte volume fraction, leukocyte count and differential count, platelet count, urine examination, and serum determinations of bilirubin, creatinine, alkaline phosphatase, aspartate amino- transferase (SGOT) and alanine aminotransferase (SGPT). The trial was conducted as a prospective randomized double-blind study in 3 parallel groups of patients, each receiving a single dose of 6 identical- looking tablets, which were swallowed with a glass of water in the presence of the investigator. The antimalarials being investigated were: sulfadoxine (S), pyrimethamine (P) amd mefloquine (M), which were administered according to the following scheme: Group 1 (25 cases): 2 tablets (corresponding to 280mg M + 800 mg S + 40 mg P) and 4 placebo tablets. Group 2 (26 cases): 3 tablets (corresponding to 420mg M + 1200 mg S + 60 mg P) and 3 placebo tablets. Group 3 (24 cases): 3 tablets (corresponding to 1500 mg S + 75 mg P) and 3 placebo tablets. The parasitological studies consisted of counts of the trophozoites and gametocytes of P.falciparum before starting treatment, followed by daily counts after treatment for 7 days and then once a week for a maximum of 4 weeks. The presence of mixed infections with P. vivax was recorded. Blood samples were collected before and 24 hours after treatment for determination of plasma concentrations of the 3 tested drugs. Treatment with 1000 mg of mefloquine was reserved for those patients who were not cured with the above treatments and in whom P.falciparum trophozoites persisted in the blood and symptoms were present. The drug was given as a single dose and these subjects were then followed up for the standard period of one month. 732 TREATMENT OF FALCIPARUM MALARIA RESULTS Parasitological response The initial parasite counts ranged from 425 to 280 000 (mean ± SD = 33 300 59 177) in group 1, from 1849 to 300 000 (mean + SD = 28 433 ± 66 496) in group 2, and from 718 to 48 300 (mean ± SD = 10 916 ± 13 064) in group 3. Considering the 75 patients together (one later dropped out), we found that most cases presented low to moderate levels of parasitaemia. Trophozoite counts were below 10 000/mm3 in 42 cases, between 10 000 and 100 000/mm3 in 30 cases, and above 100 000/mm3 in 3 cases. Clearance of the asexual blood forms of P.falciparum was obtained within 5 days in groups 1 and 2 (no cases of parasitaemia after day 5 in group 1, after day 4 in group 2), and no cases of recrudescence occurred in any patients from these two groups. The mean parasite clearance time (± SD) was 3.0 ± 1.6 days in group 1 and 2.8 ± 1.3 days in group 2. Six of the 24 patients in group 3 (sulfadoxine-pyrimetha- mine group) had to be treated with mefloquine (1000 mg) in the period between days 3 and 8 because of an unsatisfactory parasitological response; in the remaining 18 patients, clearance of asexual parasitaemia was achieved within 4 days. No recrudescences were observed, which means that the cure rate in the 50 cases treated with the two combinations of mefloquine and pyrimethamine- sulfadoxine was 100% (within the study period of 28 days), while the cure rate in the 24 patients treated with the standard dosage of pyrimethamine-sulfa- doxine was only 75%o. This difference between group 1 and 2 on the one hand and group 3 is statistically significant (Fisher's exact test, 2-tailed, P< 0.005). The gametocyte counts showed that 16 out of 23 patients in group 1, 11 out of 23 cases in group 2, and 15 out of 16 cases in group 3 had a positive gametocyte count on days 12-16. On days 25-32, only 4 out of 20 cases in group 1 and 3 out of 20 cases in group 2 still had a low gametocyte count. However, 8 out of 12 patients in group 3 still had a positive and in some cases rather high gametocyte count. The plasma concentrations of pyrimethamine and sulfadoxine, which were measured by means of a specific and sensitive microbiological assay (19) before and 24 hours after the ingestion of these drugs, showed that in 6 patients who were not cured with this treatment the levels were within the expected range, compared with those in volunteers. These findings confirm that the 6 patients had ingested and absorbed the drugs and that they were genuinely resistant to this drug combination. This resistance was classified as RI in 1 case and RII in 5 cases. Concomitant P. vivax infection was observed in 2 patients during the 1 month follow-up period and in 6 others after this period. These 8 patients remained in a non-malarious area and did not show P. vivax in the pre-treatment blood examination, which means that this form of malaria was due to relapses. All were cured with chloroquine and primaquine. Clinicalfindings No impairment of consciousness was found in any patient and the blood pressure showed no significant changes at any time. The fever was cleared in 58% of the parasitologically cured cases in group 1 within 4 days of treatment, in 641o in group 2, and in 69% in group 3. By day 7 all the patients were afebrile. Chills were not observed after day 4 in any of the cured patients. Headache and vomiting were common symptoms before treatment and did not occur after the third day of treatment. Diarrhoea occurred less frequently and persisted for a few days after therapy. Hepatomegaly (1-6 cm below the costal margin) was present before treatment in 17 patients from group 1, 15 from group 2, and 16 from group 3. At the end of the follow-up period (days 25-32), liver enlargement was recorded only three times in groups 1 and 2 and twice in group 3. Splenomegaly, following the Hackett classification, was found before treatment to be between classes 1 and 4 in 24 cases from group 1, 24 from group 2, and 22 from group 3; classes 1 and 2 were the most common finding. At the end of the follow-up period, slight splenomegaly (in most cases class 1, i.e., palpable on deep inspiration) was found in 20 patients from group 1, 20 from group 2, and 11 from group 3. Renal insufficiency was observed in only 2 patients who showed a high parasitaemia of around 300 000 per mm3 before treatment, and their symptoms subsided on day 2 after treatment. Concomitant bacterial infections were seen in 2 patients with pharyngitis and bronchopneumonia which were cured with penicillin. Side-effects. Vomiting was the only symptom that could be regarded as a side-effect of treatment. This was present with slight intensity in only three patients: two from group 1 and one from group 3. Laboratory investigations The non-parasitological laboratory determinations gave results in many cases that were outside the normal range because of the malaria; no changes were observed that could have been due to the treatment. The main findings observed were low values for Hb, erythrocyte volume fraction, RBC counts and platelet counts both before and after treatment. Raised values were seen before and after treatment for the ESR; 40 733 D. BOTERO ET AL. out of 73 cases showed raised total bilirubin values before treatment while only 5 patients still showed an increased bilirubin on days 2-4 after treatment. Raised values for alkaline phosphatase, SGPT, SGOT and creatinine were observed in several cases but the differences before and after treatment were not significant. The main finding in urinalysis was a high frequency of proteinuria, which is to be expected in symptomatic malaria. DISCUSSION A recent report on mefloquine discussed the safety, tolerance and efficacy of this drug (20). Advice was given on how the development of resistance might be prevented by following various procedures, including combination of mefloquine with pyrimethamine- sulfadoxine. The effective dose for mefloquine, when used alone, seems to be 1000 mg, administered as a single dose (21). This dose was found to be effective by us in the 6 cases that did not respond to pyrimethamine-sulfadoxine. We also found that the combination of the three drugs was not effective against the tissue forms of P. vivax, a fact found also for mefloquine alone at the standard dose (21). In our study, all 74 cases initially showed only P.falciparum, but after this infection was cured, 8 cases with P. vivax appeared. Similar findings, with an even higher P. vivax relapse rate, were found in Brazil (22) where 21 out of 99 cases were positive for P. vivax after P.falciparum was cured. These findings suggest a dominance of P.falciparum over P. vivax when both parasites are concomitantly infecting the same patient. A study in Brazil (22) recorded a 100%7o cure rate for P.falciparum with 1000 mg of mefloquine, but only 73% with the standard dose of pyrimethamine- sulfadoxine. In our study the cure rate with the latter was 7507, and with the combination of 3 drugs it was 100% (within the study period of 28 days); our combination contained only 280 mg of mefloquine in group 1 and 420 mg in group 2. A cure rate of only 19.4% with pyrimethamine-sulfadoxine was obtained in a study in Thailand, where mefloquine produced much better results (23). In the same country, a comparative study of mefloquine (single doses of 1500 mg) versus pyrimethamine-sulfadoxine (standard doses) showed a higher cure rate with the former; also gastrointestinal side-effects (nausea, vomiting, diarrhoea) were more common with mefloquine (24). In P.falciparum cases in Burma treated with mefloquine (in doses of 20 and 30 mg/kg of body weight for children and 750-1000 mg for adults) side-effects like nausea, giddiness and vomiting were noted in about 60% of the patients (25). The side-effects attributable to mefloquine in our study were infrequent since vomiting occurred in only 2 out of the 50 cases (in groups 1 and 2) who had received combinations of the 3 drugs. This good tolerance may be due to the smaller amounts of mefloquine used in our study. It is recognized that mefloquine in the therapeutic dose for P.falciparum is also effective against the blood forms of P. vivax (20) and P. malariae (26). This wide spectrum of efficacy against the three main human malaria parasites is another factor in favour of this drug. At present, however, mefloquine may not be required in regions where P.falciparum is still highly sensitive to chloroquine, as in Zambia (27). The prophylactic activity of mefloquine in drug- resistant malaria has been studied in non-immune volunteers, in whom patent parasitaemia was prevented when they were exposed to infected mosquitos two weeks after receiving a single dose of 1 g of mefloquine (28). Similar studies revealed an absence of parasitaemia during 60 days' follow-up of volunteers infected with a strain of P.falciparum resistant to chloroquine and pyrimethamine, after receiving different doses of mefloquine, with a maximum of 1000 mg every 4 weeks (29). A large comparative field trial carried out in Thailand, where different weekly doses of mefloquine and sulfadoxine-pyrimethamine were administered for 26 weeks to nearly 1000 persons, showed that mefloquine was more effective in suppressing both falciparum and vivax parasitaemias. Both groups tolerated the drugs well and no toxic effects were recorded except for leukopenia in the second group. The recommended weekly dose for a 50 kg individual was 180 mg of mefloquine, which is equivalent to 250 mg for a 70 kg person (30). The prophylactic use of mefloquine in children also gave excellent results with good tolerance (31). Nevertheless, this drug should be used only in high-risk groups in special circumstances. The possibility of a combination with primaquine as a gametocytocide and for the radical cure of vivax infections should be explored (20). The recommendation not to use mefloquine freely and to combine it with other antimalarials is mostly based on laboratory experiments which showed that resistance appeared when repeated weekly passages.of Plasmodium berghei in mice were maintained under increasing drug pressure (32). Using the P. berghei system in rodents, several mefloquine-resistant lines have been selected. All these lines lost their resistance quickly when passaged without drug pressure, and fortunately no definitely mefloquine-resistant strains of P.falciparum have so far been obtained from cultures in vitro (33). Experimental resistance to an antimalarial depends mainly on the size of the parasite population exposed to the drug pressure, but 734 TREATMENT OF FALCIPARUM MALARIA it seems the para-aminobenzoic acid content in the diet may influence this sensitivity by accelerating the development of resistance when the content of this acid is high (34). The relation of these experiments to drug resistance in human malaria has not yet been clarified. Several clinical trials with combined mefloquine and sulfadoxine-pyrimethamine treatment for P.falciparum infections have been performed during the last few years. In one study in Brazil, using 750 mg of mefloquine combined with the standard dose of the other two drugs, there was a 100% cure rate; there was good drug tolerance and rapid disappearance of the clinical symptoms (35). These results are similar to ours- 100% cure rate (S response) within the study period of 28 days, although our drug combination included smaller amounts of mefloquine. However we would not recommend using such a low dose of mefloquine in our country where there is already resistance to sulfadoxine- pyrimethamine. In order to avoid treatment failures that would favour the development of mefloquine resistance and the further spread of resistance to sulfadoxine-pyrimethamine, the dose of the combination should be high enough to ensure a fully curative effect in practically all cases. For this reason, a high-dose combination tablet containing 250 mg mefloquine, 500 mg sulfadoxine and 25 mg pyrimethamine has been developed (see above). Studies with this combination have already been performed; the results show that 2 to 3 of these higher- dose tablets are necessary to achieve a cure rate of 100% in malaria regions where chloroquine- resistance is highly prevalent and where there is also some resistance to sulfadoxine-pyrimethamine (36). ACKNOWLEDGEMENTS We are grateful to Dr R. H. Leimer and Dr A. Duarte of F. Hoffmann-La Roche, Basle, Switzerland, for their efficient contribution to the planning, developing and writing up of this study, and to the Malaria Eradication Programme, Medellin, Colombia, and the State Health Central Laboratory of the same city for their valuable cooperation. RtSUMIt ESSAI PROSPECTIF EN DOUBLE AVEUGLE DE DEUX DOSES DIFFtRENTES DE MtFLOQUINE PLUS PYRIMSTHAMINE-SULFADOXINE, PAR COMPARAISON AVEC LA SEULE PYRIMtTHAMINE-SULFADOXINE, DANS LE TRAITEMENT DU PALUDISME A FALCIPARUM La Colombie est un pays oui le paludisme pose un probleme considerable, en partie du fait de l'augmentation de la pharmacoresistance de Plasmodiumfalciparum. Cette etude avait pour objectif de tester 1'efficacite de deux doses differentes de l'association mefloquine (M) plus sulfadoxine (S) et pyrim6thamine (P), par comparaison avec la dose classique de S et de P seules, pour le traitement du paludisme a falciparum. On a traite en double aveugle, a I'aide de doses uniques, trois groupes randomises de 25, 26 et 24 hommes adultes malades, presentant une parasitemie de plus de 400 trophozoites de P. falciparum par mm3, de la facon suivante: Groupe 1 (25 cas): 2 comprimes (correspondant a 280 mgM + 800 mg S + 40 mg P) et 4 comprimes de placebo Groupe 2 (26 cas): 3 comprimes (correspondant a 420 mg M+ 1200 mg S + 60 mg P) et 3 comprimes de placebo Groupe 3 (24 cas): 3 comprimes (correspondant a 1500 mg S+75 mg P) et 3 compri- mes de placebo. Tous ces malades provenaient de regions impaludees et ont et traites et suivis dans la ville de Medellin, oui il n?y a aucune transmission du paludisme. La surveillance post- therapeutique a dure 4 semaines, des examens cliniques et parasitologiques etant pratiques tous les jours au cours de la premiere semaine, et une fois par semaine ensuite. On a procede a des analyses de sang et d'urine avant et apres le traitement, en recueillant du plasma a cette occasion, afin d'evaluer les- concentrations medicamenteuses dans le sang. Le nombre de trophoites 6tait inferieur a 10 000 par mm3 dans 42 cas, compris entre 10 000 et 100 000 par mm3 dans 30 cas et superieur a 100 000 par mm3 dans 3 cas. On a obtenu une disparition de la parasitemie (formes asexuees) en 5 jours pour les groupes 1 et 2, sans recrudescence. Sur les 24 malades suivis dans le groupe 3, 6 n'ont pas 6te gueris. La difference entre l'ensemble des groupes 1 et 2 (taux de guerison de 100%) et le groupe 3 (taux de gu6rison de 75%) est statistiquement significative. Chez les 6 malades non gu6ris, on a observe des concentrations normales de sulfadoxine et de pyrimethamine apres le traitement, ce qui confirme la resistance a ces medicaments. Cette resistance etait du type RI dans un cas et du type R2 dans les 5 autres. Tolls ces patients ont ensuite e traites avec succes a l'aide d'une dose unique de 1000 mg de m6floquine. Au cours de la periode de suivi ou juste apres on a releve la presence concomittante de P. vivax, chez 8 malades chez qui cette 735 736 D. BOTERO ET AL. espece n'avait pas e detectee avant le traitement. Les observations cliniques avant traitement correspon- daient aux symptomes habituels du paludisme a P. falci- parum, sans alteration de la conscience. L'hyperthermie, qui est le symptome principal, a disparu chez la plupart des malades gueris parasitologiquement dans les 4 jours suivant le traitement. Chez deux malades presentant une insuffisance renale avant le traitement, la parasitemie elevee, d'environ 300 000 par mm3, a rapidement cede a l'administration du medicament. Les effets secondaires ont et rares, des vomissements (sans gravite) s'etant produits chez seulement deux malades du groupe I et un malade du groupe 3. 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