It sounds counterintuitive, but apparently it seems to be the case: A pill is more effective than lotions at getting rid of resistant head lice. That's the finding of a study that compared the common malathion-based treatment lotion against Stromectal -- a pill containing ivermectin, an antiparasitic drug made by Merck (MRK).
The study, published in The New England Journal of Medicine, was sponsored by Johnson & Johnson MSD Consumer Pharmaceuticals, a European joint venture of Merck and Johnson & Johnson (JNJ).
The head louse is a parasitic insect that can be found on the head, eyebrows and eyelashes of people. Head lice feed on human blood several times a day and live close to the human scalp. They're found worldwide, aren't known to spread disease, can't jump or fly and, contrary to common belief, personal hygiene has nothing to do with whether you get them. An estimated 6 million to 12 million infestations occur each year in the U.S. among children 3 to 11 years of age. Worldwide, head lice affect more than 100 million people each year.
While there are several over-the-counter medications to treat head lice that often work, malathion is a commonly prescribed lotion. The problem is that lice have become resistant to the insecticides in pyrethroid- and malathion-based products, according to the authors of the trial. Also, poor adherence to the treatment guidelines -- in many cases, the lotion has to be left in the hair for 10 to 12 hours before being washed out -- often leads to ineffective treatment.
The study, conducted in 812 infected people from 376 households in four countries, found that 95.2% of patients receiving the pill were lice-free on day 15, compared with 85% of those receiving malathion. And perhaps because the nuisance of using the lotion, more patients preferred taking the pill to using the lotion. The researchers concluded that ivermectin could be used as an alternative treatment in hard to treat cases. The pill is given twice at a seven-day interval.
Recommended So Far Only for Hard-to-Treat Cases
Ivermectin is an oral broad-spectrum antiparasitic medication also used to treat river blindness, threadworm and scabies. The authors of the study -- some of whom were employed by or had financial relationships with the companies that sponsored the trial -- add that there were no reported severe adverse events in patients using the drug so far, although the dose for other indications is usually lower than that used in the trial for head lice.
Moreover, several parasites treated with ivermectin have begun to show resistance to the drug, which suggests that lice, too, could develop resistance to it over time. Therefore, they recommend using ivermectin only on difficult to treat cases -- those who do not respond to lotion treatment.
As the maker of the pill, Merck no doubt wants a piece of the $100 million a year market for head lice treatment, even if its treatment isn't marketed as a front-line therapy. Doctors have already been prescribing Stromectal in some cases.
The question is whether a pill with side effects that include dizziness, nausea and sleepiness, and may even have more serious -- though rare -- side effects is necessary as a treatment for something that is a mild condition, not a disease. Only last month, the FDA approved another lotion for the treatment of head lice. Whether to request Stromectal is a question parents may have to answer depending on their child's individual case.