PracticeUpdate: Dermatology - Winter 2018

EXPERT OPINION 20

Itching to Prescribe the Right Treatment for Scabies: Topical Permethrin or Oral Ivermectin? By Warren R. Heymann MD

Dr. Heymann is Professor of Medicine and Pediatrics and Head of the Division of Dermatology at Cooper Medical School of Rowan University, and Clinical Professor of Dermatology at Perelman School of Medicine at the University of Pennsylvania in Philadelphia, Pennsylvania.

T hree weeks after confirming the diagnosis of crusted scabies on an HIV-positive patient, I started to scratch while driving in the parking lot at Cooper University Hospital (New Jersey). I didn’t give it much thought until the next day, when this stinging–itching sensation wouldn’t relent (interestingly, the scratch- ing felt soooo gooood). I realized that I probably had acquired scabies. After a colleague identified the mite, the hardest part of this process was telling my wife and daughters that they needed treatment too. The family episode of permethrin applica- tion undoubtedly led to my preference for prescribing oral ivermectin whenever pos- sible – it is so much easier to take pills. Have I been recommending substandard therapy? Scabies is an infestation of the skin by the mite Sarcoptes scabiei . Transmission is by direct skin-to-skin contact or indi- rectly through fomites. Symptoms typically appear 3 to 6 weeks after an infestation. In patients with a prior exposure to the mite, symptoms can appear as early as 24 hours post exposure. Lesions consist of pruritic erythematous papules with excoriations. They’re usually symmetrical and involve the interdigital webs, the flexural aspect of wrists, the axillae, the peri-umbilical area, elbows, buttocks, feet, genital area in men, and the peri-areolar area in women. The entire integument, including the face and

the scalp, can be involved in infants, the elderly, and immunosuppressed patients. The pathognomonic sign is the burrow, rep- resenting the tunnel that the female mite digs to lay its eggs. Crusted scabies (CS) is a severe form that occurs in immunosup- pressed individuals, such as patients with AIDS, manifesting with extensive hyperker- atosis, predominantly over the scalp and the extremities. 1 The two first-line treatments for scabies are topical permethrin 5% cream and oral ivermectin. According to Powell and Tucker, “oral ivermectin in single doses of 200microgm/kg has been shown to be very effective in a number of studies, although it is not more effective than properly applied permethrin.…Its safety in children under 15 kg in weight is unknown. Oral ivermec- tin should therefore be reserved for when appropriate application of a topical anti- scabetic is not possible or practicable – for example, compliance, severe eczematiza- tion, or as a part of a treatment regimen in crusted/hyperkeratotic and resistant cases. However, randomized controlled trials examining oral ivermectin in crusted scabies are lacking. Treatment with per- methrin is repeated after 1 week, as it may not be effective against scabies mite eggs. This repeat treatment allows time for any such eggs not destroyed by the first treat- ment to hatch so the hatchlings may then be killed. Similarly, oral ivermectin may not

PRACTICEUPDATE DERMATOLOGY