Combination therapies useful for severe scabies cases

Dr. StonePanama City, Panama - Different agents have become available for scabies treatment, but topical permethrin cream 5 percent is still the go-to therapy, according to an expert. In combination with oral ivermectin, even the most challenging cases of scabies can be addressed effectively.

“Permethrin is a very safe and effective agent used for scabies and still remains as our treatment of choice for the infestation,” says Stephen P. Stone, M.D., professor and director of clinical research, division of dermatology, Southern Illinois University School of Medicine, Springfield, Ill. “Fortunately, there has not been a significant emergence of resistance to permethrin due to the nature of the toxicity to the scabies mite.”

Lindane, also known as gamma-hexachlorocyclohexane used to be the first line of treatment for scabies, however the agent has fallen into disuse in the United States because of the possibility of toxicity. Nevertheless, it is still considered an excellent back-up treatment where it is available, according to Dr. Stone, who spoke recently at the annual meeting of the North American Clinical Dermatologic Society.

Combination approach

Oral ivermectin is often used as a second-line therapy for scabies in the United States and has also been proven to be effective. For more severe cases of scabies, however, such as Norwegian scabies (crusted scabies), Dr. Stone says a combination approach using both topical permethrin cream 5 percent together with oral ivermectin appears to be very useful.

In one recent study, the efficacy of a single dose of oral ivermectin was compared to two treatments of topical permethrin applied at a one-week interval for the treatment of scabies. Results showed an 85.9 percent cure rate in those patients who received a single dose of ivermectin, compared to a 93 percent cure with topically applied permethrin.

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Although the cure rates were very similar, the investigators concluded that permethrin was the superior agent for the treatment of scabies, and suggested that ivermectin may not be effective against all the stages in the life cycle of the parasite (Goldust M, Rezaee E, Hemayat S. J Dermatol. 2012;39(6):545-547).

“When used in combination, a single dose of ivermectin and two doses of permethrin can really result in a very good cure, and can be particularly useful in the more severe and recalcitrant cases of scabies,” Dr. Stone says.

Next: Quelling the itch

Addressing pruritus

In his patients with scabies, Dr. Stone says he often treats with permithrin cream, and depending on the severity of the itch that typically is seen in affected patients, he will also prescribe a topical corticosteroid such as 0.1 percent triamcinolone cream or administer a triamcinolone injection to help quell the itch.

“Scabies infestation is one of the itchiest skin diseases we see and anti-pruritic agents such as calamine lotion are often insufficient in addressing the itch,” he says. “Quite frankly, if I have someone who is really excoriated and scratching a lot, I will give them the treatment with permithrin but I will also give them an injection of triamcinolone intramuscularly.”

One of the biggest challenges for managing patients with scabies is to make the accurate diagnosis, Dr. Stone says. Here, clinicians should perform scrapings whenever possible to help confirm the diagnosis under the microscope, leading to appropriate and timely therapy.

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The best way of diagnosis would be to actually find the mite, which was traditionally achieved via skin scrapings and if possible, shaving off the top of the burrow and viewing it under the microscope. According to Dr. Stone, the dermatoscope has simplified the diagnosis of scabies, as one can magnify the area and see the burrow and with luck, the mite itself in the burrow.

Another new diagnostic method is the SCAB (superficial cyanoacrylate biopsy) specimen approach, according to Dr. Stone. It involves a drop of super glue placed on the burrow, upon which a microscope slide is then placed. After a few seconds, the slide is peeled off the skin, taking with it the mite and/or sometimes the ova of the mite, viewable under the microscope.

“The techniques available today for the diagnosis of scabies have made it a lot easier to confirm diagnosis, which can lead to a more timely therapy. It is very important to confirm your diagnosis if at all possible, as this eliminates doubt if tried therapies do not work,” Dr. Stone says.

Disclosures: Dr. Stone reports no relevant financial interests.