Medications that kill head lice are called pediculicides. All pediculicides except malathion are applied to the scalp and hair and left on for 10 minutes, then rinsed off. Pediculicides kill nymphs and adult lice, but do not destroy nits. For this reason, they may need to be reapplied 7-10 days after the first application to kill newly emerged nymphs. Because some pediculicides have significant toxicities, it is important to follow application directions carefully.
Permethrin is the preferred first-line treatment for head lice. Permethrin 1% (Nix) is available over the counter, and permethrin 5% (Elimite) is available by prescription. Permethrin is a cream rinse that is designed to leave a residue after rinsing that kills emerging nymphs, so reapplication is usually not needed.
Pyrethrins Plus Piperonyl Butoxide (Rid)
Rid is a shampoo that can cause an allergic reaction in people who have plant allergies, especially allergies to chrysthanthemums. Twenty to thirty percent of the eggs remain viable after treatment, so a second treatment is recommended in 7-10 days.
Lindane is available only by prescription. It should only be used cautiously if a first-line treatment has failed because several cases of seizures in children have been reported.
Malathion is a prescription lotion that is applied to the hair, left to air dry, then washed off after 8-12 hours. Because it has a high alcohol content, it is highly flammable and can cause difficulty breathing if it is ingested. For these reasons, it should only be used for resistant cases of head lice.
Trimethoprim-sulfamethoxazole (Septra, Bactrim) is an oral antibiotic, given as a 10-day course, which has been shown to be effective at treating resistant infestations of head lice. Ivermectin (Stromectol) is an antiparasitic drug given as a single dose that has also been shown to effectively treat resistant head lice infestations. However, neither of these drugs is FDA approved for use as a pediculicide.
Treatment with a pediculicide kills adult lice and nymphs preventing the spread of head lice infestation to other people. Removal of nits is recommended to reduce confusion about the effectiveness of treatment. Nits within 1 cm of the scalp should be physically removed by a fine toothed comb. A variety of agents are available to break down the cement holding the nit to the hair shaft including distilled white vinegar, formic acid preparations, and enzymatic nit removal systems. Using one of these agents prior to nit combing makes it easier to remove nits. Nits that are present on the hair shaft greater than 1 cm from the scalp are not considered to be viable and do not have to be removed.
Treatment of Head Lice Contacts
According to the American Academy of Pediatrics, if a case of head lice is identified, all household members should be checked for head lice. Only those with live lice or eggs within 1 cm of the scalp should be treated. It is also recommended that all hair care items and bedding belonging to the infested person be cleaned.