RECENT MILITARY EXPERIENCE WITH MALARIA CHEMOPROPHYLAXIS

Objective: To assess the value of various drug regimens for malaria pr ophylaxis under circumstances where dapsone and pyrimethamine (combine d as Maloprim) and chloroquine, followed by the 14-day primaquine erad ication course, were no longer effective in protecting military person nel against falciparum and vivax malaria. Design, setting and particip ants: Various drug regimens given to four groups of healthy male membe rs of the Australian Army during training exercises in malarious count ries. Interventions: Four groups of soldiers were given different regi mens for 3-12 weeks: Group 1 - mefloquine (250 mg weekly); Group 2 - d oxycycline (1 00 mg daily); Group 3 - doxycycline (100 mg daily) and p rimaquine (7.5 mg daily); and Group 4-doxycycline (50 mg daily) and ch loroquine (300 mg weekly). Except in Group 3, each of these regimens w as followed by a 7.5 mg dose of primaquine three times a day for two w eeks. Main outcome measures: The proportion of participants in the var ious prophylactic drug groups who developed falciparum or vivax malari a during or after the intervention. Results: Group 1:40 men receiving mefloquine were all protected against falciparum malaria but four (10% ) developed vivax malaria. These results were not statistically differ ent from those obtained for either falciparum (P=0.28) or vivax (P=0.3 6) malaria in the control group of 64 men receiving Maloprim and chlor oquine. Group 2: 60 men receiving doxycycline (no control group) were all protected against falciparum malaria but two developed vivax malar ia. Group 3: 124 men, of whom 55 received doxycycline and 69 primaquin e in addition to doxycycline, were all protected against falciparum ma laria. However, 13 men taking only doxycycline developed vivax malaria two to three weeks after prophylaxis, whereas no vivax infections wer e observed in the men taking the drug combination (P=0.0001). Group 4: no malaria infections were observed in 125 men receiving doxycycline and chloroquine for 13 weeks, probably because of the low prevalence o f malaria in the training area. Conclusions: These studies confirm tha t doxycycline is very effective in preventing falciparum malaria and, for the first time, also suggest that doxycycline used in combination with small doses of primaquine may prevent (not only suppress) vivax m alaria. If further studies confirm these findings, the use of such a d rug combination would reduce the incidence of both vivax and falciparu m malaria in returning travellers. For individuals with a high risk of exposure to malaria, it would also forestall the need to take the bot hersome primaquine eradication course.