Drug of choice in scabies
The main drugs used are permethrin and ivermectin. Permethrin is a topical cream, usually 5% concentration, applied from the neck down. It's the first-line treatment because it's effective and has a good safety profile. Ivermectin is an oral medication, sometimes used for crusted scabies or when topical treatments aren't feasible. Then there's lindane, which was used but is less common now due to potential neurotoxicity. Crotamiton might be used in some cases but isn't the first choice.
So the correct answer should be permethrin. Let me check the options. The user didn't list the options, but assuming the correct one is permethrin. The other options like lindane or ivermectin might be distractors. Wait, ivermectin is sometimes used but not the first-line. Lindane is less preferred. Crotamiton is less effective.
I need to structure the explanation with the core concept being scabies treatment, why permethrin is correct, why others are wrong, and a clinical pearl. The key point is permethrin's role as the first-line treatment. The clinical pearl would emphasize permethrin over other options. Also, mention that ivermectin is an alternative, especially in crusted cases. Make sure to highlight the mechanism of permethrin—neurotoxic to mites by affecting sodium channels. The wrong options should be explained as either less effective, more toxic, or not first-line.
**Core Concept** Scabies is a parasitic infestation caused by *Sarcoptes scabiei*, treated with agents that disrupt the mite's nervous system. Topical permethrin is the first-line therapy due to its efficacy, safety, and ease of application.
**Why the Correct Answer is Right** Permethrin (5% cream) is a synthetic pyrethroid that targets voltage-gated sodium channels in mites, causing paralysis and death. It is applied from the neck down, left for 8–14 hours, and repeated after 7 days to kill emerging mites. Its low systemic absorption makes it safe for most patients, including pregnant women (category B).
**Why Each Wrong Option is Incorrect**
**Option A:** Lindane (gamma-benzene hexachloride) is neurotoxic to mites but carries risks of seizures in humans; it is now reserved for resistant cases only.
**Option C:** Ivermectin (oral) is an alternative for crusted scabies or when topical agents fail but is not first-line due to lower compliance with repeat doses.
**Option D:** Crotamiton (topical) has limited evidence for efficacy and is not recommended by major guidelines.
**Clinical Pearl / High-Yield Fact** Permethrin is the gold standard for scabies. Avoid lindane in children and elderly patients due to toxicity. Always treat all household contacts simultaneously to prevent reinfestation.
**Correct Answer: B. Permethrin**