Malathion Lotion 0.5% (Ovide — Medicis)
October 30, 1999
Pharmacology Update
Malathion Lotion 0.5% (Ovide—Medicis)
By William T. Elliott, MD, FACP, and James Chan, PharmD, PhD
After an absence of several years, malathion lotion is returning to the market for the treatment of head lice. It will again be marketed under the trade name Ovide by Medicis, and is available by prescription only. Malathion was pulled off the market twice (as Prioderm and Ovide) because of poor sales, primarily the result of a strong odor and difficulty in using the product. But with the increase in head lice resistant to pyrethrins and permethrin, malathion remains effective against pediculosis. The product is also the only available product that kills not only the lice, but the eggs (nits).
Indications
Malathion is indicated for the treatment of head lice resistant to pyrethrins and permethrin.
Dosage
Malathion is applied to dry hair and scalp and left in place for 8-12 hours. The hair should be washed thoroughly afterward and a fine-tooth comb should be used to remove the nits. The treatment can be repeated in 7-9 days if lice are still present.1 Malathion lotion should not be used on infants.
Malathion is flammable and, therefore, must be kept away from heat sources such as hair dryers, cigarettes, or any open flames.
Potential Advantages
Malathion has been shown to be a pediculicidal and ovicidal in vitro.2 It also binds to hair, thus providing residual protection.1
Potential Disadvantages
Malathion lotion is not cosmetically pleasing due to its unpleasant odor. It must be left on for 8-12 hours and is flammable. The alcoholic vehicle may cause stinging, particularly if applied to irritated or inflamed skin.
Comments
Malathion is an irreversible cholinesterase inhibitor with pediculicidal and ovicidal activity. In a double-blind study in patients with long-standing lice infestation, malathion was reported to be highly efficacious—95% (62/65) of treated patients remained lice-free after seven days.3 In a comparative study in Europe, malathion was found to be superior to d-phenothrin, a synthetic pyrethroid. Seven days after treatment, the success rate (absence of live lice and viable nits) was 95% for malathion and 39% for d-phenothrin.5
The average wholesale cost of Ovide is $31 for 60 mL.
Clinical Implications
Pediculosis is a result of head lice infestation most commonly in child care and school-age children. The infestation is achieved through direct head-to-head contact but can be transmitted by sharing of combs, hats, or hair accessories. All socioeconomic groups are affected, but Caucasians may be affected more than other ethnic groups. Treatment should be considered if active lice or viable eggs are observed. Permethrin and pyrethrins are the treatments of choice. Since the nits are generally resistant to these agents, a second treatment is recommended 7-10 days later. Lice resistant to permethrin have recently been reported in this country, although the prevalence of resistance to permethrin is not known.4 Using a higher strength of permethrin generally does not increase effectiveness.4 Malathion lotion may be considered if lice persist after two treatments with permethrin or pyrethrin. Lindane has fallen out of use due to potential toxicity and resistance.1 Ivermectin has been reported to be effective against resistant lice but is not effective as an ovicide.1
More information on head lice can be obtained from the National Pediculosis Association website, www.headlice.org.
References
1. The Medical Letter 1999;41:73-74.
2. Meinking TL, et al. Arch Dermatol 1986;122:267-271.
3. Taplin D, et al. JAMA 1982;247:3103-3105.
4. Pollack RJ, et al. Arch Pediatr Adolesc Med 1999; 153(9):969-973.
5. Chosidow O, et al. Lancet 1994;344:1724-1727.
Malathion is pediculicidal but not ovicidal.
a. True
b. False
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