What dose of ivermectin should be given to a patient weighing 179 pounds (81 kilograms) with persistent pruritus (itching) after two treatments with permethrin cream for scabies?

From the Guidelines

For a patient weighing 179 lbs (approximately 81 kg) with persistent scabies symptoms after two treatments with permethrin cream, the recommended dose of ivermectin is 200 ug/kg, which calculates to approximately 16.2 mg as a single oral dose, as stated in the 2015 guidelines for sexually transmitted diseases treatment 1. This dose should be taken with food to enhance absorption, as bioavailability is increased when taken with food 1. The dose may need to be repeated after 1-2 weeks if symptoms persist, as this ensures elimination of newly hatched mites. Some key points to consider when treating scabies with ivermectin include:

• Ivermectin works by paralyzing and killing the Sarcoptes scabiei mites by binding to glutamate-gated chloride channels in their nerve and muscle cells.
• Common side effects may include headache, dizziness, muscle pain, and mild gastrointestinal symptoms.
• It's essential to note that ivermectin doesn't kill the eggs of the mites, which is why a second dose is often necessary.
• The patient should also wash all bedding, clothing, and towels in hot water and dry on high heat to prevent reinfestation. It's also important to consider the potential for crusted scabies, an aggressive infestation that usually occurs in immunodeficient, debilitated, or malnourished persons, and may require combination treatment with a topical scabicide and oral ivermectin 1. However, for a patient with persistent symptoms after two treatments with permethrin cream, the recommended dose of 200 ug/kg is a reasonable starting point, and the patient should be monitored for response to treatment and potential side effects 1.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Strongyloidiasis The recommended dosage of STROMECTOL for the treatment of strongyloidiasis is a single oral dose designed to provide approximately 200 mcg of ivermectin per kg of body weight. Onchocerciasis The recommended dosage of STROMECTOL for the treatment of onchocerciasis is a single oral dose designed to provide approximately 150 mcg of ivermectin per kg of body weight

The patient weighs 179 lbs, which is approximately 81 kg.

• For Strongyloidiasis, the dose would be approximately 200 mcg/kg, so 81 kg x 200 mcg/kg = 16,200 mcg or 16.2 mg.
• For Onchocerciasis, the dose would be approximately 150 mcg/kg, so 81 kg x 150 mcg/kg = 12,150 mcg or 12.15 mg. However, the FDA label does not provide dosage information for scabies. The FDA drug label does not answer the question.

From the Research

Dosing of Ivermectin for Scabies

• The treatment dose for non-crusted scabies is 200 µg/kg, taken in a single dose with food 2.
• To calculate the dose of ivermectin for a patient weighing 179 lbs, first convert the weight to kilograms: 179 lbs / 2.2 lbs/kg = 81.4 kg.
• Then, calculate the dose: 200 µg/kg * 81.4 kg = 16,280 µg or 16.3 mg.
• Since ivermectin is typically produced in 3 mg tablets (e.g., Stromectol), the patient would need approximately 5-6 tablets (16.3 mg / 3 mg per tablet) 2.

Retreatment

• Retreat in 10-14 days to enhance effectiveness, and perhaps to reduce scabicide resistance 2.

Efficacy and Safety

• Oral ivermectin is safe, easier to use, cheaper, more effective, and more economical than topicals in widespread institutional scabies, for those nonadherent to topicals, and in crusted scabies 2.
• The efficacy and safety of ivermectin compared to other treatments, such as permethrin, have been studied, with mixed results 3, 4, 5, 6.