Study recommends malathion as first-line treatment for head lice

New York - A new study suggests that malathion should be used as a first-line treatment of head lice infestation in children and that therapy for head lice should be based on the life cycle of the lice, drug resistance and safety considerations, Medscape news source reports.

The study, conducted by researchers at New York’s Mount Sinai School of Medicine in New York and appearing in the May issue of Pediatrics, notes that traditional pharmacological therapies for head lice have focused on one or two courses of various ovicidal and pediculicidal topical therapies, and within the past 20 years lice have developed resistance to nearly all first-line pharmacotherapy in this country.

Treating with an agent to which lice have developed genetic resistance is unproductive, the study says.

“The American Academy of Pediatrics recommends permethrin 1 percent as first-line treatment for head lice, a medicine for which resistance in the United States is extensively documented,” the researchers write.

In the United States, they add, lice have become increasingly resistant to pyrethroids and lindane but not to malathion. Other advantages of malathion treatment are its favorable efficacy and safety profiles and that it allows children's immediate, safe return to school.

The study also notes that in treating head lice, physicians should take into consideration the timing of head lice maturation most favorable to their survival when exposed to anti-lice agents: the maximum time as an ovum (12 days) and the shortest possible time of maturing from newly hatched nymph to egg-laying adult (8.5 days).

Based on review of life-cycle considerations, therapeutic mechanisms of action, development of resistance and head lice biology, the study recommends malathion, in the formulation containing isopropyl alcohol and terpineol, as the favored agent for head lice treatment. At any given time, the study says, a head lice patient will have lice existing at different points in the life cycle, and the only therapy that will ensure eradication when used properly is malathion.

The study notes that there are concerns about malathion’s reported flammability, but adds that these concerns may be ill-founded. The study says there are no known reports of bodily injury resulting from the isopropyl alcohol catching fire, but adds that appropriate precautions should be taken to avoid heat sources during use.

The study also notes that one of the authors has disclosed he is vice president and a major shareholder of Taro Pharmaceutical Industries Ltd., which makes and markets Ovide malathion lotion. The other authors disclosed no relevant financial relationships.