Permethrin is used in the topical treatment of:
## **Core Concept**
Permethrin is a synthetic **pyrethroid** insecticide and acaricide used in the treatment of various ectoparasitic infestations. It acts by disrupting the sodium channels in the nerve cells of the parasites, leading to their death. This class of drugs is particularly effective against a range of parasites.
## **Why the Correct Answer is Right**
The correct answer, **Scabies**, is a skin infestation caused by the mite *Sarcoptes scabiei*. Permethrin cream is a first-line treatment for scabies due to its efficacy and safety profile. It is applied topically and has a high cure rate for this condition. The mechanism of action involves the disruption of the mite's nervous system, ultimately leading to its death.
## **Why Each Wrong Option is Incorrect**
- **Option A: Pediculosis** - While permethrin can be used to treat pediculosis (infestation by lice), it's more commonly associated with the treatment of scabies. Other treatments like **pyrethrin** shampoos and **malathion** lotions are also effective for pediculosis.
- **Option B: Leishmaniasis** - This is a protozoal infection transmitted by sandflies. The treatment of leishmaniasis typically involves **antimonials**, **amphotericin B**, or other specific antiprotozoal drugs, not permethrin.
- **Option C: Tinea infections** - These are fungal infections of the skin, hair, and nails caused by dermatophytes. The treatment for tinea infections involves **antifungal** agents like terbinafine, griseofulvin, or topical agents like clotrimazole.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that permethrin is often the drug of choice for scabies, especially in children and pregnant women, due to its safety and efficacy. A common regimen is a single application of 5% permethrin cream from neck to toes, left on for 8-14 hours before washing off.
## **Correct Answer:** D. Scabies