Topical and Oral Anti-Parasitics

What Topical and Oral Medications Are Used to Treat Parasites? 

Common parasitic infections of the skin include head lice (Pediculus humanus capitis), body lice (Pediculosis corporis), pubic lice (Pediculosis pubis), and scabies (Sacroptes scabiei).

A less common parasite that infects the skin is the hookworm, which can cause cutaneous larva migrans. Upon diagnosis of a parasitic skin infection, patients are usually given a topical anti-parasitic medication as the first line of treatment. In cases of severe, resistant, or recurrent infections, oral anti-parasitic medications may be prescribed. See Table 1 for a list of topical and oral anti-parasitic medications.

*Brand names in parenthesis

How Do Topical and Oral Anti-Parasitic Medications Work?^[1]

• Permethrin – inhibits important sodium channels on parasite cell membranes, leading to parasite paralysis and death^[2]
• Malathion – kills lice by inhibiting an enzyme in them called cholinesterase^[2]
• Benzyl alcohol – kills lice by suffocation^[2]
• Spinosad – kills lice by causing central nervous system overexcitation^[3]
• Lindane – causes seizures and death of parasites
• Ivermectin – leads to paralysis and death of parasites
• Crotamiton – unknown mechanisms of action against Sarcoptes scabiei
• Albendazole – leads to the death of parasites by degrading parasites’ intestines and depleting their energy

What Conditions Do Anti-Parasitic Medications Treat? 

How Are Anti-Parasitic Medications Given?

Topical anti-parasitic medications are typically given as a single application, although repeat applications are commonly required to eradicate the infection. Oral anti-parasitic medications are most commonly given once or twice per day for at least seven days. However, some infections may only require a single dose while others may require extended treatment beyond seven days.^[14]

• Permethrin – For head lice, the permethrin solution should be applied to the entire scalp and dry hair. After soaking for approximately 10 minutes, the permethrin can be rinsed out with water and the treatment should be repeated on day nine.^[15]  For treatment of scabies, permethrin cream should be applied to the entire body, including the soles of the feet and under fingernails and toenails to kill the live scabies mites. The cream can be washed off after approximately 10 hours. Most physicians will require a second application one to two weeks later in order to kill any scabies eggs that might have hatched in the time since the first application.^[16]
• Ivermectin – For both lice and scabies, oral ivermectin is often given as a single dose with a second dose given approximately one week later.^[16] 

What Are Common Side Effects and Risks of Anti-Parasitic Medications?