Malathion lotion as an insecticide and ovicide in head louse infestation.

A lotion containing 0.5% malathion was compared with its vehicle (control) in a double-blind, parallel-group study of 119 patients with head louse infestations confirmed by live ova in the hair. The lotions remained in place for 8 hours. The test preparation was superior to the control lotion by a highly significant margin (p less than 0.001) as determined by the numbers of patients with live lice at 24 hours and 7 days after removal of the respective materials. It also proved superior to the vehicle (p less than 0.001) as an ovicidal agent, judged by comparative differences in hatching rates between nits collected and incubated before treatment and those obtained and incubated after treatment. No adverse reaction occurred.