Prevention of venous thromboembolism by administration of hydroxychloroquine. A preliminary report.

A placebo or the antimalarial agent hydroxychloroquine (Plaquenil), which inhibits platelet adhesiveness, and, to a lesser extent, platelet aggregation, was given to 100 patients between forty and ninety-five years old (average age, seventy-four years) who had either fractures or orthopaedic operations involving the skeleton between the knee and the pelvis. Medication was started at the time of admission in a blind, randomized way, fifty patients receiving hydroxychloroquine (200 milligrams three times a day) and fifty, a placebo. No untoward bleeding complications were noted in the treated group. Eight instances of thromboembolism were encountered in the control group as compared with one in the hydroxychloroquine-treated group, a statistically significant difference at the 1.5 per cent level.