Oral Ivermectin May Be Superior to Malathion Lotion in Head Lice Treatment

Nancy Fowler Larson

March 12, 2010

March 12, 2010 — Treating head lice with oral ivermectin (Stromectol, Merck) is more effective than applying malathion lotion (Ovide, Taropharma) in difficult-to-treat children, according to a study published March 11 in the New England Journal of Medicine. Affecting more than 100 million people worldwide annually, head lice are most apt to plague children 3 to 11 years old. Typical first-line treatment consists of topical insecticides, but resistance to many such lotions is widely documented.

"Resistance of lice to insecticides, particularly pyrethroids, results in treatment failure," write Olivier Chosidow, MD, PhD, from the Department of Dermatology, Hôpital Henri Mondor, Créteil, France, and colleagues. "The efficacy of alternative agents is controversial."

The study sought to evaluate the efficacy and safety of oral ivermectin (400 μg/kg) compared with malathion lotion (0.5%) in children whose conditions had proven resistant to topical insecticides.

For a 6-month period beginning in March 2004, the cluster-randomized, double-blind, double-dummy, controlled trial was conducted at 7 centers in the United Kingdom, Ireland, France, and Israel. Included in the study were children at least 2 years of age and 15 kg in weight whose head lice were not cured after topical insecticide treatments within 2 to 6 weeks before study enrollment. A total of 376 households with 812 patients, median age 10 years old, participated in the study, with each household defining a cluster.

Ivermectin and malathion were given on days 1 and 8. A lack of head lice on day 15, confirmed by researchers using a fine-tooth comb, was the primary outcome measured.

Ivermectin More Effective in Every Measurement

On day 15, the results showed more patients in the ivermectin group were cured of lice in each of 3 measurements:

  • 95.2% (378/397) of intention-to-treat patients given ivermectin were free of head lice compared with 85.0% (352/414) of those who received malathion (absolute difference, 10.2 percentage points; 95% confidence interval [CI], 4.6 - 15.7; P < .001).

  • 97.1% of per protocol subjects in the ivermectin group were lice-free compared with 89.9% of participants in the malathion group (absolute difference, 7.3 percentage points; 95% CI, 2.8 - 11.8; P = .002).

  • 92.4% of clusters receiving ivermectin had no head lice compared with 79.1% of households in the malathion group (absolute difference, 13.4 percentage points; 95% CI, 6.4 - 20.4).

Adverse events in 7 of the 398 (1.8%) patients given ivermectin and 5 of 414 (1.2%) patients treated with malathion led to discontinuation of treatment. Only 3 events were considered severe.

The study's chief stated limitation was the fact that only self-reporting was used to gather information about the failure of previous insecticide treatments. Another limitation was linked to the relatively few adverse events in children between ages 2 and 5 years compared with other age groups.

Of concern to the researchers were some reports of resistance to ivermectin. To curb that risk, they suggested ivermectin only for those whose head lice failed to respond to first-line topical treatments.

Better Malathion, Safety Concerns May Prevent Wide Ivermectin Use in United States

The American Academy of Pediatrics (AAP) recommends the relatively new malathion only after other insecticides have failed. The risks of malathion include the fact that it is highly flammable and that it can cause respiratory depression if swallowed.

AAP guidelines for ivermectin state that 200 μg/kg, repeated in 10 days, may be effective, but warn against its use in children who weigh less than 15 kg.[1] Common adverse effects of ivermectin include nausea, bloating, diarrhea, headache, lightheadedness, and muscle aches. Rare adverse effects include facial swelling and seizures. Ivermectin is approved by the US Food and Drug Administration (FDA) for treatment of several other parasites, but not for head lice.

US physicians are not likely to prescribe ivermectin off-label for head lice, according to Barbara Frankowski, MD, MPH, from the Department of Pediatrics, University of Vermont, Burlington, and lead author of the AAP policy statement[1] on head lice. In an interview with Medscape Medical News, Dr. Frankowski called the European study "carefully prepared and well done" but noted that there are several reasons why its results may be a moot point for US medical practice.

First, US physicians are unfamiliar with ivermectin. Second, the malathion available in the United States is more potent than that found in Europe. Finally, topical treatments only allow a small amount of medication to be absorbed by the body, limiting their potential for harm. Because head lice is a benign condition, it does not warrant taking a health risk, Dr. Frankowski explained.

"No one has ever died of head lice," Dr. Frankowski said. "You want to make sure the treatment is absolutely safe; you never want to use a treatment with worse side effects than what you're treating."

Dr. Frankowski also noted that US physicians have a new treatment alternative: topical benzyl alcohol lotion (Ulesfia, Sciele Pharma), which was recently approved for head lice by the FDA, but is not available for use in Europe. Benzyl alcohol, which asphyxiates the lice, is safe and unlikely to have resistance issues.

No study has yet compared any dosage of ivermectin to the US-approved malathion lotion. Should the medications be shown to produce the same results, however, Dr. Chosidow would in that case recommend ivermectin only as a third-line treatment.

"If a patient failed to respond to malathion, then one would go to ivermectin," Dr. Chosidow told Medscape Medical News.

Another wrinkle in the application of the findings is that the 400 μg/kg double dose of ivermectin taken by study subjects cannot be prescribed by physicians in the United States or Europe, Dr. Chosidow said.

"If one wants to cure head lice, the higher dose is efficacious, but for the moment it has not been approved by FDA or European agencies," Dr. Chosidow said. "We don't know the long-term impact of the higher dosage."

Johnson & Johnson-Merck Sharp & Dohme-Chibret supported the study. Dr. Chosidow and 2 other study authors received consulting fees from Johnson & Johnson during the study time period. Study authors also reported holding stock options in Johnson & Johnson and Merck, or being employed by Johnson & Johnson-Merck Sharp & Dohme-Chibret during the study. A full list of disclosures is available at the end of the journal article.

N Engl J Med. 2010;362:896-905. Abstract

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