KOHALA COAST, HAWAII — Attack hyperkeratotic scabies both topically and systemically or your treatment will fail, Timothy G. Berger, M.D., said at a conference on clinical dermatology sponsored by the Center for Bio-Medical Communications Inc.
He divides patients with scabies into two categories to guide management—those with a low burden or a high burden of disease. For the typical patient with a low burden, two applications of permethrin 5% cream a week apart will cure 95% of cases.
But a double whammy usually is needed for patients with a high burden of disease—those with crusted or hyperkeratotic scabies, AIDS and scabies, or scabies acquired while in a long-term care facility or prison, said Dr. Berger of the University of California, San Francisco.
He prefers to use these two categories because patients with a high burden of disease may present with multiple papules instead of crusts, but need the combination therapy used for crusted scabies.
The combination treatment consists of weekly applications of permethrin 5% cream for 3–6 weeks plus ivermectin 200 mcg/kg every 2 weeks for two (or occasionally three) doses. The patient should show improvement by 3 weeks into treatment and continue to gradually improve.
Don't try to save a buck by skimping on the ivermectin, he warned. Don't round down the dose but, rather, give the full dose of ivermectin (usually 12–18 mg), and allow plenty of time to treat. “Every time it has failed, I've undertreated,” Dr. Berger said. In appropriate doses, the combination therapy has never failed him.
Don't be dissuaded from suspecting scabies just because a patient has failed permethrin treatment or family members seem unaffected, Dr. Berger advised.
Treat the whole family, but not necessarily immediately. Family members who are affected get immediate treatment, but otherwise Dr. Berger waits to treat the family until the primary patient has been treated, so that the patient is no longer infectious.
High-burden cases often involve the scalp, so instruct patients to apply permethrin to the scalp too, he advised. Ivermectin won't help scabies involving the nail plate, so consider more aggressive treatments for nail scabies.
Ivermectin is secreted in sebum, he noted, which is one reason monotherapy may not work in the elderly, children, malnourished patients, or people with Down syndrome, all of whom make less sebum.
Immunosuppression plus neural disease puts patients at risk for crusted scabies, one reason that people with AIDS or Down syndrome are at higher risk for crusted scabies, he said.