Malaria prophylaxis with proguanil and sulfisoxazole in children living in a malaria endemic area.

Malaria prophylaxis with proguanil and sulfisoxazole in children living in a malaria endemic area" L.W. Pang,1 N. Limsomwong,l P. Singharaj,l & C.J. Canfield2 The effects of three separate antimalarial prophylactic regimens (proguanil, sulfisoxazole, and proguanil plus sulfisoxazole) and of vitamins in a control group were compared in a study population of 380 children living in a malaria endemic area along the Thai-Burmese border. The subjects, aged 5-16 years, were matched for age, weight, and presence of splenomegaly, then randomly assigned to one of the four groups. All medications were administered daily by the investigators and malaria smears were performed on a weekly basis. Among 99 subjects taking proguanil plus sulfisoxazole for a total of 1464 man-weeks, there was only one case of falciparum and no vivax malaria. Statistically, this regimen proved superior to each of the other groups against both Plasmodium falciparum and P. vivax. The data show that proguanil alone, as a causal or suppressive prophylatic, has poor efficacy against P. falciparum. Side-effects were infrequent and generally mild, except for two subjects whose sulfisoxazole prophylaxis was discontinued because of urticarial rash. During the past three decades, falciparum malaria in Thailand has been showing increasing resistance to both treatment (1-7) and prophylaxis (8, 9) with various drugs including chloroquine, pyrimethamine plus sulfadoxine (Fansidar), and quinine. Because of this multidrug resistance, a combination of quinine plus tetracycline is generally required to treat falci- parum malaria in this country (10). For chemo- prophylaxis two currently available drugs have been shown to be effective in Thailand: mefloquine, administered weekly (11), and doxycycline, which has recently been shown to be effective when adminis- tered daily (12). Neither drug has beer, 'ised widely for malaria prophylaxis and the long-term tolerance and safety are unknown. Recently, we began to re- evaluate an older chemoprophylactic, proguanil, which has been used widely and has a long history of safety. Proguanil, initially used for both treatment and prophylaxis of falciparum malaria in Asia during the 1940s and 1950s, became ineffective because of the development of drug resistance by both Plasmodium falciparum and P. vivax (13-15). Some felt that the prophylactic failures were suppressive failures (i.e., due to inability of proguanil to inhibit the erythro- cytic stages) and that the drug may still work caus- ally against the exo-erythrocytic stages (16). * The opinions or assertions contained in this article are the private views of the authors and are not to be construed as offi- cial or as reflecting the views of the Department of the Army or the Department of Defense. Requests for reprints should be sent to Dr L. W. Pang, P.O. Box 52, Tripler Army Medical Center, Hawaii 96859-5000, USA. 1 U.S. Army Medical Component, Armed Forces Research Insti- tute of Medical Sciences, Bangkok, Thailand. 2 Pharmaceutical Systems, Inc., Gaithersburg, MD, USA. Compared with other antimalarials, proguanil is relatively free of side-effects. There are virtually no contraindications for its use and it is one of the few antimalarials recommended for use during preg- nancy (17, 18). Because of its low cost, low toxicity, and recent data suggesting prophylactic benefits against falciparum malaria (19, 20), we tested this drug against Thailand's multidrug-resistant strains of P.falciparum (21); compared with a control group given chloroquine, we found that daily proguanil was a poor prophylactic in Thailand. In 1973 Black observed in Viet Nam that 200 mg proguanil, administered daily, worked poorly as a falciparum malaria prophylactic until a sulfa drug, dapsone, was added (22). Since then, widespread P. falciparum resistance has developed rapidly to sulfa drugs and other antimalarials, notably Fansidar which was effective in south-east Asia during the mid 1970s (6, 7, 9). It would not be surprising if present strains show marked resistance to proguanil-plus- sulfa regimens since, like Fansidar, their theoretical mechanism of action is as a hydrofolate-reductase inhibitor. Black's important finding needs to be re- examined in the light of today's highly drug-resistant strains of P.falciparum in south-east Asia. We chose to test proguanil combined with the sulfonamide, sulfisoxazole. The decision to use sul- fisoxazole was based on its short half-life, its prophy- lactic use in children against otitis media (23, 24) and meningitis (25, 26), and its widespread availability. Furthermore there is evidence that sulfa drugs with shorter half-lives may have less severe side-effects compared to those with longer half-lives, which are thought to be the cause of some of the severe side- effects seen during long-term prophylactic use of Fansidar (27-29). The purpose of the present study Bulletin of the World Health Organization, 67 (1): 51-58 (1989) © World Health Organization 1989 51 L.W. Pang et al. was to evaluate the malaria prophylactic efficacy of a combination of daily proguanil plus sulfisoxazole, compared with each drug alone and a control group. Materials and methods The study was performed during a 17-week period from October 1986 to February 1987 in the Karen refugee camp of Mae Thawaw located on the Thai- Burmese border. The study population, consisting of schoolchildren aged 5 to 16 years, had nearly all lived in this forested area with high malaria trans- mission for at least three years. Chemoprophylactic studies had previously been done in this study popu- lation; the most recent one was completed two months before the start of the present study. Addi- tional information on the study site and population, and on the drug-sensitivity pattern of P. falciparum in this area has been presented previously (12, 21). Physical examination of the study population showed no signs of malnutrition. This study was approved by the Thai Supreme Command Human Use Committee, The Karen Refugee Committee, and the Walter Reed Army Institute of Research Scientific Review Board. Antimalarial drugs were administered to the study population only by the investigators or by Medicin Sans Frontieres (MSF) staff at an on-site clinic; the latter administered therapeutic antima- larials only after referral by the study investigators of cases with positive malaria smears. Prior to entering the study, the subjects were interviewed and examined for signs of chronic illnesses and splenomegaly. Blood samples for the following laboratory values were obtained: WBC with differential, erythrocyte volume fraction (haematocrit), ASAT (aspartate aminotransferase), ALAT (alanine aminotransferase), alkaline phospha- tase, total and direct bilirubin, and blood urea. Infor- mation sheets and consent forms were explained to the subjects' parents in their native language prior to their granting permission for their children to enter the study. Children who fulfilled the following cri- teria were admitted to the study: age, 5 to 16 years; haematocrit, greater than 25%; WBC count, greater than 3 x 109/l; informed consent signed by the parent for study participation; and no evidence of chronic, debilitating disease other than malaria. The subjects were stratified according to age, weight, and presence of splenomegaly. Within each stratum, sub- jects were randomly assigned to one of four study groups. Group 1 received proguanil HCl (Imperial Chemical Industries) at a dose of 100 mg daily for those weighing less than 20 kg, or 200 mg daily for those greater than 20 kg. Group 2 received sul- fisoxazole (Gantrisin, Roche Laboratories), 75 mg per kg body weight daily in a single dose. Group 3 received the combination regimen of proguanil plus sulfisoxazole (dosages as above). Group 4 was administered vitamins daily. The recommended adult dose of proguanil is 200 mg daily, either alone or in combination with chloroquine (19). The corre- sponding dose for children less than 20 kg should be 100 mg; for children between 20 and 40 kg, 150 mg; for those greater than 40 kg, 200 mg (18). Because of the available pill formulation, subjects between 20 and 40 kg received doses slightly higher than the corresponding adult dose of 200 mg. All subjects were asked a standard set of ques- tions concerning symptoms or side-effects before each dose. Every child was identified by name and photograph before being given the appropriate medication, in a non-blinded manner, by one of the investigators. Subjects were observed till they had swallowed the pills and then consumed a small amount of food. Malaria smears (Giemsa stained, thick and thin) were taken at weekly intervals and when there were complaints of fever, headache, or backache. At least 200 fields of thick film were examined before report- ing a smear as negative. Smears showing only gametocytes were tallied as negative. Technicians reading the smears had no knowledge of the subjects' medications. Children who had positive smears for either falciparum or vivax malaria were referred to MSF staff for treatment. Those with falciparum malaria received a single dose of MSP (mefloquine + sulfadoxine + pyrimethamine) plus a single dose of primaquine; those with vivax malaria received four doses of chloroquine plus daily pri- maquine for 14 days. In this region the efficacy of each treatment regimen is greater than 97% (unpublished data). Therapy was started within 24 hours of slide reading. Subjects received no antima- larials other than those for the study. The investiga- tors observed all drug administrations except for the second dose of chloroquine that was given for vivax malaria. Prophylactic medications were withheld during treatment and restarted 15 days after initi- ation of vivax therapy or 21 days after falciparum treatment. For those who missed appointments, drug administration and smears were resumed on their return. In order to minimize the number of subjects presenting with patent or subpatent parasitaemias at the start of the study, all subjects were screened with weekly smears starting 8 weeks prior to the start of the study. Cases detected during this interval were treated with the above regimens. All reported symptoms were regarded as pos- sible side-effects if they occurred during drug prophylaxis and were not attributable to malaria 52 Malaria prophylaxis with proguanil and sulfisoxazole Table 1: Baseline characteristics of children receiving proguanil, or sulfisoxazole, or proguanil plus sulfisoxazole, or vitamin, Mae Thawaw, October 1986-February 1987 Proguanil plus Proguanil Sulfisoxazole sulfisoxazole Vitamin group group group group (n = 92) (n = 99) (n=99) (n =90) Mean age (years) 9.7 9.7 9.5 9.5 Mean weight (kg) 23.5 23.4 23.2 22.6 Splenomegaly (%) 9.8 13.3 12.1 12.0 Mean haematocrit (%) 38.7 38.5 39.0 38.2 Mean WBC (x 109/l) 8.5 9.3 8.7 9.1 infections (i.e., they did not occur within five days of such a diagnosis or while on treatment). Fever was included as one of these symptoms to evaluate the role of sulfisoxazole in preventing bacterial infec- tions. Upon completion of this study the subjects were examined for splenomegaly; laboratory mea- surements were also repeated and any abnormal values occurring after drug administration (compared with normal pre-drug-administration values) could be attributed to the drugs. Data analysis Data regarding malaria incidence and drug side- effects were analysed over the entire study period. Survival analysis using man-week units was used to compare the malaria (falciparum and vivax) attack rates among the groups. Only periods (man-weeks) occurring after at least one negative smear followed by uninterrupted drug administration were counted. When a lapse in medication occurred due, for example, to the child's absence or when malaria therapy was given, that subject was "re-entered" into the study upon demonstration of a negative smear. Regarding side-effects, the frequency of reported symptoms was calculated by tallying the episodes (man-days) of a reported symptom as well as the number of individuals experiencing each symptom. Since man-days are used, the denominators (i.e., total man-days of medication administration) used to cal- culate the frequency of side-effects (Table 5) are larger than the denominators (i.e., man-weeks of uninterrupted medication administration) used to calculate the malaria attack rates (Tables 2 and 3). For example, if a subject missed a single day of medicine, that week is not counted in the tally of prophylactic efflicacy, but six days of drug adminis- tration are tallied for evaluation of side-effects. Spe- cific statistical tests used are described in the results section. Results A total of 92, 99, 99, and 90 children were assigned to the groups receiving proguanil, sulfisoxazole, pro- guanil plus sulfisoxazole, and vitamin, respectively. Measurements prior to the start of the study showed that the groups were comparable with respect to age, Table 2: Number of cases of malaria (faiciparum and vivax) and participation by tudy week among children receiving daily proguanil, or sulflsoxazole, or proguanil plus sulfisoxazole, or vitamin, Mae Thawaw, October 1986-February 1987 Proguanil plus Proguanil Sulfisoxazole sulfisoxazole Vitamin group group group group Study weeks (n = 92) (n = 99) (n = 99) (n =90) 1, 2 1/148 (0)' 0/173 (0)' 0/176 (0)" 3/163 (4)' 3, 4 1/166 (1) 1/178 (0) 0/186 (0) 2/157 (3) 5, 6 2/152 (6) 3/173 (2) 1/176 (0) 4/158 (5) 7, 8 1/153 (4) 2/173 (0) 0/175 (0) 0/161 (5) 9, 10 2/153 (2) 2/163 (0) 0/167 (0) 3/153 (6) 11, 12 2/154 (1) 4/168 (4) 0/161 (0) 4/151 (4) 13, 14 1/148 (0) 0/152 (3) 0/162 (0) 1/142 (4) 15, 16 0/151 (1) 2/163 (0) 0/175 (0) 1/144 (3) 17 0/75 (1) 1/82 (0) 0/86 (0) 0/74 (1) Total 10/1300 (16) 15/1425 (9) 1/1464 (0) 18/1303 (35) Number of cases of falciparum malaria/number of man-weeks; cases of vivax malaria are given in parentheses. 53 LW. Pang et al. Table 3. Number of cases of falciparum and vivax malaria by the weeks of drug administration among children In the proguanil, sulflsoxazole, proguanil plus suHlfsoxazole, and vitamin groups, Mae Thawaw, October 1986-February 1987 Proguanil plus Proguanil Sulfisoxazole sulfisoxazole Vitamin group group group group No. of weeks on drug (n = 92) (n = 99) (n = 99) (n =90) 1, 2 2/320 (3)' 5/351 (1)' 0/324 (0) 8/316 (12)8 3, 4 4/253 (6) 2/264 (2) 1/266 (0) 3/250 (8) 5, 6 1/192 (4) 3/202 (2) 0/213 (0) 4/192 (4) 7, 8 1/146 (1) 2/166 (0) 0/177 (0) 1/154 (6) 9, 10 1/122 (2) 1/133 (3) 0/145 (0) 1/121 (4) 11, 12 1/95 (0) 2/110 (1) 0/118 (0) 1/96 (0) 13, 14 0/74 (0) 0/88 (0) 0/98 (0) 0/78 (0) 15, 16 0/68 (0) 0/75 (0) 0/86 (0) 0/67 (1) 17 0/30 (0) 0/36 (0) 0/37 (0) 0/29 (0) Total 10/1300 (16) 15/1425 (9) 1/1464 (0) 18/1303 (35) Number of cases of falciparum malaria/number of man-weeks; cases of vivax malaria are given in parentheses. weight, frequency of splenomegaly, haematocrits and WBC counts (P > 0.05 for all values, X2-test for fre- quency of splenomegaly and ANOVA for others) (Table 1). Nine (9.8%), seven (7.1%), eleven (11.1%), and ten (10.8%) of the subjects from the proguanil, sul- fisoxazole, proguanil plus sulfisoxazole and vitamin groups, respectively, were absent from the camp during more than 60% of the study (either dropped out or enrolled late), while the remaining subjects missed 2.1%, 1.7%, 2.6%, and 2.9% of their sched- uled appointments, respectively. Falciparum and vivax prophylactic failures and man-weeks of participation (tallying only periods of uninterrupted prophylactic drug administration) for each study week are shown in Table 2. The number of man-weeks of participation varies because of lapses in drug administration, subjects on malaria therapy, and subjects resuming prophylaxis after absences. The risk of contracting falciparum malaria was not constant throughout the study period, but the proportion of total weeks of participation during the higher transmission period, i.e., weeks 1-12 (as seen in the control group), were comparable among all groups (proguanil = 71%, sulfisoxazole = 72%, pro- guanil plus sulfisoxazole = 71%, vitamin = 72%). The risk of contracting vivax malaria was approx- imately constant throughout the study except during the last two weeks. Falciparum and vivax prophylactic failures and man-weeks of participation are listed by the number of weeks of complete drug administration in Table 3. There were 10, 15, 1 and 18 falciparum malaria breakthroughs, occurring after at least one negative smear followed by uninterrupted drug adminis- tration, in the proguanil, sulfisoxazole, proguanil plus sulfisoxazole, and vitamin groups, respectively. There were significantly fewer failures on proguanil plus sulfisoxazole compared to either proguanil (P < 0.01), sulfisoxazole (P < 0.001), or vitamin (P < 0.001), using survival analysis (Breslow statistic). After at least 8 days of uninterrupted drug administration (negative smears on days 0 and 7) Table 4: Suppressive prophylactic failures (Indicated by the number of falclparum and vivax malaria cases) by para- site counts and the occurrence of symptoms, Mae Thawaw, October 1986-February 1987 No. of malaria cases Proguanil plus Proguanil Sulfisoxazole sulfisoxazole Vitamin group group group group Parasite count (per 100 WBC) Falciparum Vivax Falciparum Vivax Falciparum Vivax Falciparum Vivax <1 1 5 1 5 0 0 0 8 (1)' 1-10 4 (1)' 6 5 (1) 3 0 0 4 (1) 16 (1) 11-100 2 (1) 3 5 (2) 0 1 (1) 0 8 (1) 8 (6) >100 3 (1) 2 (1) 4 (4) 1 0 0 6 (5) 3 (3) Figures in parentheses are the number of cases with symptoms at the time of diagnosis. S4 Malaria prophylaxis with proguanil and sulfisoxazole there were 8, 11, 1 and 13 failures against P. falci- parum, respectively. Similarly, after 15 days (negative smears on days 0, 7, 14) there were 8, 10, 1, and 10 failures, respectively. Regarding vivax malaria, there were 16, 9, 0, and 35 breakthroughs in the proguanil, sulfisoxazole, proguanil plus sulfisoxazole, and vitamin groups, respectively. Comparing the vitamin group to each of the others showed levels of significance at or below 0.005 (survival analysis, Breslow statistics). P. falciparum prophylactic failures presented with significant parasitaemias and clinical symptoms (Table 4). It is unlikely that the parasitaemias would have cleared spontaneously without treatment, nor would proguanil or sulfisoxazole, used alone, be able to limit the parasitaemias once breakthroughs did occur. No subject who was considered a prophylac- tic failure reported vomiting of the drug prior to the positive smears. Slde-ffects. Reported symptoms that were regarded as possible drug side-effects are presented as the number of episodes and number of individuals reporting the symptom in Table 5. Overall, symp- toms were few, mild, and transient. There was signifi- cantly more dizziness, nausea, and vomiting in the proguanil plus sulfisoxazole group compared with the controls (P < 0.001, X2-test). Dizziness was also reported more often in the proguanil group. The group on sulfisoxazole alone had fewer episodes of fever, headache, and abdominal pain (P < 0.05, x2- test) than did the control group, but this observation was not true in the group receiving sulfisoxazole and proguanil. One subject each from the sulfisoxazole and from the proguanil plus sulfisoxazole groups devel- oped urticarial rash which resolved after discontin- uation of the medication and inclusion into the vitamin group. Both subjects were ambulatory and had no trouble in eating or drinking. For one subject on proguanil we discontinued the drug because of frequent complaints of headache and dizziness, beginning three months after the start of medication. Paired blood samples before and after drug administration were obtained on 81, 89, 88, and 77 subjects in the proguanil, sulfisoxazole, proguanil plus sulfisoxazole, and vitamin groups, respectively, and were tested for total and direct bilirubin, ASAT, ALAT, alkaline phosphatase, blood urea, haemato- crit and WBC. In all four drug groups, the post-trial values for haematocrit, WBC, and ALAT were sig- nificantly greater (P < 0.025, paired t-test). Table 6 shows values which were initially normal but became abnormal during the study. For elevated WBC counts the number of individuals in each group is presented instead of the actual counts. At the time of the second blood sampling there was in the camp an epidemic of upper respiratory tract infections, which was the probable cause of the elevated WBC counts in all groups. Discussion This study of prospective field testing of three drug regimens for their prophylactic efficacy against both falciparum and vivax malaria was conducted in an area of multidrug-resistant P. falciparum. For both types of malaria the combination of proguanil plus sulfisoxazole proved statistically superior to either drug used alone, as well as to the control group. By closely monitoring our study population confined within the endemic area we were able to enforce Table 5: Frequency of symptoms (not attributable to malaria Infection) occurring during administration of study medi- cations, Mae Thawaw, October 1966-February 1987 No. of episodes Proguanil plus Vitamin Proguanil Sulfisoxazole sulfisoxazole (control) group group group group Fever 127 (44)' 107b(40) 158 (49) 149 (36) Headache 84 (24) 52b(26) 87 (32) 72 (29) Dizziness 68C(25) 42 (19) 78C(32) 42 (21) Nausea 10 (7) 8 (6) 22C(12) 5 (4) Vomiting 8 (6) 6 (5) 19C(12C) 5 (3) Abdominal pain 10 (7) 8b (6) 17 (13) 18 (9) Diarrhoea 10 (7) 9 (4) 6 (3) 4 (4) Rash 3 (3) 6 (6) 9 (9) 0 (0) Total number of man-days on drug 10964 11 764 11 720 11084 Figures in parentheses indicate the number of individuals with the symptom. b Significantly less than control group (P < 0.05). c Significantly greater than control group (P < 0.05). 55 L.W. Pang et al. Table 6: Laboratory abnormal results that developed during the study (after Initially normal values) Proguanil plus Proguanil group Sulfisoxazole group sulfisoxazole group Vitamin group (n = 81) (n = 89) (n = 88) (n = 77) Erythrocyte volume fraction" (<0.30) 0 0 0 lb WBCC(>11.5 x 109/l) 27 16 23 17 Bilirubin (>25.6 umol/l)' 0 0 0 0 ALAT (>45 U/l)d 46, 160, 60 125, 92, 48, 48 48 48, 48, 52 ASAT (>50 U/l)d 60, 52, 66, 112, 60, 55, 69, 52, 58, 66 58, 80, 63, 52, 52, 51 72, 72 63, 55, 60, 58, 58, 143, 52, 60 Alkaline phosphatase (>15 U/l)' 0 0 0 0 Blood urea (>8.9 mmol/l)' 0 0 0 0 Figures denote number of individuals with an abnormal value. b One individual had a low reading (0.29). c Numbers of individuals with elevated WBC counts. d Figures are abnormal values. compliance with drug administration and reporting of side-effects, conduct adequate follow-up for case detection, restrict self-administration of non-study antimalarials, and ensure equal malaria risk among the study groups. In addition, this study provides data which support previous suggestions that proguanil's pro- tection against south-east Asian strains of P. falci- parum is poor (21, 30). Breakthroughs occurring after at least one negative smear followed by uninter- rupted drug administration represent suppressive prophylactic failures. If the drugs were administered throughout the prepatent period as well, then the breakthroughs represent both suppressive and causal prophylactic failures. Eight of the ten breakthroughs on proguanil occurred after more than two weeks of administration. These failures represent (1) suppress- ive failures following longstanding subpatent infec- tions, (2) suppressive failures following prolonged prepatent periods, or (3) causal (and suppressive) fail- ures. Longstanding subpatent infections are unlikely because of the study population's low malaria immu- nity, as shown by the low prevalence of sple- nomegaly and presence of symptoms and significant parasitaemias at the time of slide confirmation. Fur- thermore, during weekly screening for eight weeks prior to the start of the study, the subjects either remained negative or were administered an effective therapy for falciparum malaria. Though certain anti- malarials, notably the sulfa drugs, can significantly prolong prepatent periods, a small study by Clyde showed that proguanil lengthened the prepatent period an average of only one day (range, 1-3 days) (31). In the light of the above observations we feel that these eight breakthroughs probably represent causal prophylactic failures, implying causal prophy- lactic efficacy of approximately 50%. We hope, but cannot be certain, that our find- ings can be applied to nonimmune populations. Because our study population may have a low degree of immunological protection, a nonimmune group administered proguanil plus sulfisoxazole would perhaps show poorer protection under similar malaria exposure. The same argument applies to proguanil used alone, with the possibility that the efficacy in nonimmunes would be worse than what we have shown. Because of logistical and ethical constraints, P. falciparum isolates from prophylactic breakthroughs were not routinely tested for in vitro drug sensiti- vities, nor were blood samples obtained for serum drug levels. Since it is unknown whether the progua- nil plus sulfisoxazole regimen is acting as a causal and/or suppressive prophylactic, we were uncertain whether in vitro drug-sensitivity testing on the blood stages would truly reflect prophylactic efficacy. Others feel that there is a correlation in the develop- ment of parasite resistance to proguanil between the exoerythrocytic and the erythrocytic stages (32). Because the Thai strain of P. falciparum is so highly drug resistant, we feel that prophylactic regi- mens, such as proguanil plus sulfisoxazole which was shown to be effective in this region, are probably effective in other areas of the world. Conversely, regi- mens which show poor efficacy here, such as progua- nil, may still provide significant protection elsewhere, where strains are less drug resistant. However, before recommendations for proguanil prophylaxis (either alone or in combination with other drugs) are made in those regions, the efficacy should be shown in well-controlled trials. The 1-2% incidence of dermal reactions in sub- jects on sulfisoxazole seen in this study is not sur- prising (33). More importantly, we did not see more 56 Malarla prophylaxis with proguanil and sulflsoxazole severe toxic reactions such as Stevens-Johnson syn- drome or agranulocytosis/leucopenia, a significant drawback for prophylactic use of the longer-acting sulfa drugs against P. falciparum (8, 30, 34, 35). Our study numbers are small and much larger groups need to be monitored for side-effects before general recommendations regarding sulfisoxazole plus pro- guanil can be considered. Therefore, we do not advo- cate general use of this drug combination at this time. However, this research can serve as a basis for future studies evaluating malaria prophylaxis and side-effects of this combination. Such studies should include: 1) close monitoring of subjects for side- effects, 2) evaluation of lower doses and alternative, analogous drugs, 3) development of in vitro tests to correlate with in vivo sensitivity patterns, 4) determi- nation of the mechanism of prophylactic action, causal or suppressive, and 5) evaluation of the effi- cacy in nonimmune populations and in other geo- graphical areas with different drug-sensitivity patterns of P.falciparum. In keeping with WHO's guidelines (36), we do not advocate the use of any drug for general, mass chemoprophylaxis. Effective, safe agents should be reserved for high-risk groups such as pregnant women or travellers to endemic areas. Chemopro- phylaxis might also be considered for short-term use in specific populations under controlled settings, e.g., for labour forces or military units. Acknowledgements We thank Jeerawan Thanoosingha, Sumetha Hengpra- sert, Prapapis Pittayapisute, Amphon Na-Nakorn, and Dumrong Charoendham for their technical assistance; Dr Brian Schuster and Dr Jerome Karwacki for guidance during the study and review of the manuscript; and Vallapa Naewthai for typing the manuscript. This study was supported by the U.S. Army Research and Development Command. Resume Prophylaxie du paludisme par le proguanil et le sulfisoxazole chez des enfants des zones d'endemle L'efficacite prophylactique de I'administration quo- tidienne de proguanil + sulfisoxazole contre le paludisme a faiciparum et a vivax a ete examinee lors d'un essai de terrain realis a la frontiere birmano-thallandaise, une zone de poly- pharmacoresistance de Plasmodium falciparum. Des enfants figes de 5 a 16 ans, dont on avait re,u le consentement informe des parents, ont ete stratifies par age, poids et presence d'une spleno- megalie, et repartis au hasard dans quatre groupes d'etude. Un des groupes recevait du pro- guanil a raison de 100 mg par jour pour les enfants de moins de 20 kg et 200 mg par jour pour les enfants de plus de 20 kg. Un deuxieme groupe a re,u du sulfisoxazole (75 mg/kg par jour en une dose unique). Un troisieme groupe a re,cu le traite- ment associe proguanil + sulfisoxazole (memes doses que ci-dessus). Un quatri6me groupe, servant de temoin, a re,u une dose quotidienne de vitamines. Toutes les doses ont ete administrees par les chercheurs en essai ouvert. Aucun enfant n'a re,u d'autres antipaludiques que les medica- ments inclus dans l'etude; toutefois, en cas de necessite, un traitement antipaludique etait administre sous la surveillance des chercheurs (mefloquine/sulfadoxine/pyrimethamine pour le paludisme a faiciparum et chloroquine/primaquine pour le paludisme a vivax). Les enfants ont et6 interroges quotidiennement au sujet d'eventuels symptomes et effets secondaires. Des preleve- ments de sang ont ete realises en vue d'epreuves de laboratoire au debut et a la fin de I'etude. Des frottis ont ete realises chez tous les sujets une fois par semaine et en cas de sympt6mes evoquant le paludisme. Les chercheurs, qui ignoraient a quel groupe appartenaient les sujets etudies, ont obser- ve les lames a la recherche d'une parasitemie, et devaient examiner 200 champs en goutte epaisse avant de classer une lame comme negative. L'etude a dure d'octobre 1986 a f6vrier 1987. Les groupes se composaient de 92 enfants pour le proguanil, 99 enfants pour le sulfisoxazole, 99 enfants pour le proguanil + sulfisoxazole et 90 enfants pour le groupe temoin; on obtenait ainsi l'equivalent, respectivement, de 1300, 1425, 1464 et 1303 semaines-hommes de traitement ininter- rompu. On a trouve respectivement 10, 15, 1 et 18 lames positives pour P. falciparum et 16, 9, 0 et 35 lames positives pour P. vivax dans les quatre groupes. Le traitement associe s'est montre sta- tistiquement superieur a chacun des medicaments et au groupe temoin en ce qui concerne la protec- tion contre le paludisme a falciparum et a vivax. II est a noter que sur les 10 cas positifs pour P. falci- parum dans le groupe recevant le proguanil, huit sont apparus au bout d'au moins deux semaines d'administration du medicament (frottis negatifs les jours 0, 7 et 14), ce qui suggere un echec de la prophylaxie causale. Dans l1ensemble, les symp- tomes etaient benins et transitoires, le groupe recevant le traitement associe ayant mentionne plus souvent des vertiges, nausees et vomisse- ments que les temoins. Deux des sujets recevant le sulfisoxazole ont presente une urticaire. L'examen de laboratoire (leucocytes, fonction hepatique, azote ureique du sang) ne montrait 57 L.W. Pang et al. aucune anomalie particuliere par rapport aux te- moins. References 1. Harlnasuts, T. et al. Chloroquine-resistant falciparum malaria in Thailand. 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