New Options for Eradicating Resistant Head Lice

Marcia L. Buck, Pharm.D., FCCP, FPPAG

Disclosures

Pediatr Pharm. 2012;18(6) 

In This Article

Ivermectin Lotion, 5%

The most recent addition to the market is a topical preparation of an antiparasitic drug used enterally for more than 20 years in the US. In a recent comparison trial, oral ivermectin demonstrated efficacy in 95% of difficult-to-treat cases, including permethrin treatment failures, compared to only 85% of patients treated with topical malathion.[11] Topical administration of ivermectin has long been proposed as an equally effective method for lice eradication without the risks of systemic exposure, but until now there has been no commercially available preparation.[12]

Like other avermectins, ivermectin selectively binds to glutamate-gated chloride channels in invertebrate nerve and cell muscles which leads to increased permeability to chloride and hyperpolarization, resulting in paralysis and death. It may also bind to gamman-aminobutyric acid (GABA)-gated chloride channels, augmenting this response. Ivermectin has low affinity for mammalian ligand-gated chloride channels and limited penetration into the central nervous system, reducing its potential for toxicity. Ivermectin has little to no ovicidal activity.5,13

Ivermectin 0.5% lotion (SKLICETM, Sanofi Pasteur, Inc) is indicated for the treatment of head lice in patients 6 months of age and older.[5] The product contains the following inactive ingredients: water, olive oil, oleyl alcohol, Crodalan AWS (an emollient), lanolin alcohol, cyclomethicone, shea butter, sodium citrate, sorbitan tristearate, methyparaben, propylparaben, and citric acid.

The efficacy and safety of ivermectin 0.5% lotion were studied in two phase III multicenter randomized, double-blind, vehicle-controlled studies.[5] A total of 289 subjects 6 months of age and older were enrolled. As in the studies for the previously described agents, the primary endpoint was the proportion of subjects lice-free at day 14. In the first study, 54 of the 71 treated subjects (76.1%) were lice-free, compared to only 12 of the 74 subjects (16.2%) given only the vehicle. Similar results were obtained in the second study, with 71.4% of the 70 treated subjects and 18.9% of the 74 controls free of lice at 14 days.

Ivermectin lotion should be applied to dry hair in an amount sufficient to cover the hair and scalp. The lotion should be left on for 10 minutes, then rinsed off with warm water. Use of a nit comb is not necessary, but may be helpful to remove dead lice and nits. The individual applying the lotion should carefully wash his or her hands after coming into contact with the lotion. To date, ivermectin 0.5% lotion has only been studied as a single treatment.[5]

Adverse effect data were pooled from 379 adult and pediatric patients treated in the premarketing clinical trials.[5] The most commonly reported adverse effects (all occurring in less than 1% of patients) included: conjunctivitis, eye irritation or redness, dry skin, dandruff, or a skin burning sensation). Accidental ingestion may result in headache, dizziness, nausea, vomiting, diarrhea, rash, pruritus, edema, paresthesias, or shortness of breath.

The pharmacokinetic profile of topical ivermectin was evaluated in 20 infants and children (ages 6 months to 3 years) taking part in the premarketing clinical trials.[5] The mean maximum plasma ivermectin concentration was 0.24 + 0.23 ng/mL, much lower than the concentrations achieved with oral administration. Ivermectin has not been studied in infants less than 6 months of age because of the potential for increased topical absorption in this population and the risk for systemic toxicity.

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