Head lice, Pediculus humanus capitis, are tiny, wingless insects living on the human scalp and feeding on blood. These common parasitic infestations primarily affect children but can spread to all ages. Ivermectin is a medication recognized for its efficacy in treating various parasitic conditions, including head lice, in both humans and animals.
How Ivermectin Acts on Lice
Ivermectin binds to glutamate-gated chloride ion channels in invertebrate nerve and muscle cells. This increases cell membrane permeability to chloride ions. The influx of chloride ions hyperpolarizes the cell, hindering nerve and muscle function. This disruption leads to paralysis and death of the parasite. The drug’s mechanism targets processes unique to invertebrates, contributing to its safety in humans.
Approved Forms and Usage
Ivermectin is available in topical and oral formulations for treating head lice. Topical ivermectin, typically available as a lotion or solution, is generally applied to dry hair and scalp. The application usually involves leaving the product on for a specific duration before rinsing. A single application is often sufficient.
Oral ivermectin is administered as tablets, typically as a single dose, sometimes followed by a second dose seven to ten days later. The U.S. Food and Drug Administration (FDA) has approved topical ivermectin lotion, 0.5%, for treating head lice in individuals aged 6 months and older. Oral ivermectin has also received FDA approval for head lice treatment in individuals weighing at least 15 kg. Both forms are prescription medications, and their use requires guidance from a healthcare professional to ensure proper dosage and administration.
Efficacy and the Challenge of Resistance
Ivermectin is effective in eliminating head lice infestations, with high success rates in killing both lice and nits. Its different mechanism of action compared to older pediculicides is beneficial. However, its effectiveness, like any lice treatment, can be influenced by resistance. Lice can develop genetic mutations that reduce their susceptibility to active ingredients over time.
Pediculicide resistance occurs when treated lice survive and reproduce, passing on resistant genes. Widespread use or misuse of medication can accelerate this process, reducing efficacy in certain areas. While effective, ivermectin’s success can vary depending on local resistance patterns. Healthcare providers consider regional resistance when recommending treatment.
Safety Profile and Precautions
Ivermectin is generally well-tolerated when used as directed for head lice treatment, but it can cause side effects. For topical formulations, common reactions include skin irritation, itching, or redness at the application site. Oral ivermectin may lead to systemic side effects such as dizziness, nausea, vomiting, or abdominal pain. These effects are typically mild and transient.
Certain precautions are important before using ivermectin. It is generally not recommended for pregnant or breastfeeding individuals due to limited safety data in these populations. Young children, particularly those under 6 months for topical forms or weighing less than 15 kg for oral forms, may also have restrictions on use. Individuals with underlying liver conditions or those taking certain medications should consult a healthcare professional, as ivermectin can interact with other drugs. Adherence to prescribed dosages and application instructions is important to minimize potential adverse effects.