Mefloquine chemoprophylaxis of soldiers on the Thai-Cambodian border.

Chemoprophylaxis of malaria on the Thai-Cambodian border is difficult due to the high level of drug resistance. Thirteen separate companies of Royal Thai Marine Militia were placed on 250 mg weekly mefloquine chemoprophylaxis from August 1989 to January 1990. A mean number of 722 soldiers received two or more doses of mefloquine per month for the five month study. The medication was well tolerated and compliance averaged 91%. Substantial numbers of prophylaxis breakthroughs were seen which resulted in 3.2 cases of malaria/100 man-months. Sixty-eight falciparum malaria cases were documented in men who had taken at least two mefloquine doses in the previous four weeks. No serious neuropsychiatric reactions occurred. Mefloquine chemoprophylaxis failures exist on the Thai-Cambodian border and are one sign of the spread of mefloquine resistance.