Dermatology/Antiparasitic (skin)

Scabies & lice treatments

also: permethrin scabies · dimeticone head lice · malathion

Overview

Topical antiparasitics for scabies and head lice — the "treat the whole household" and application rules are the exam points.

Mechanism

Permethrin (pyrethroid) is neurotoxic to the mite/louse (Na-channel disruption → paralysis). Dimeticone physically coats and suffocates lice. Ivermectin (oral) paralyses parasites via glutamate-gated chloride channels (crusted scabies).

Indications

Scabies
Head lice (pediculosis)
Crusted (Norwegian) scabies — add oral ivermectin

The agents

Permethrin 5% creamscabies 1st-line

whole body, wash off 8–12 h

Treat ALL household/close contacts simultaneously; repeat after 1 week; itch persists weeks after cure.

Dimeticone 4% / wet combinghead lice

Physical agents preferred (less resistance).

Malathionalternative

Scabies/lice second-line.

Oral ivermectincrusted scabies

Plus topical for severe/crusted/outbreaks.

Adverse effects

Local irritation / itch (persists post-treatment)common

Counsel: itch ≠ treatment failure for up to 4 weeks.

Stinging on applicationcommon

Cautions & contraindications

—all

Topicals well tolerated; permethrin safe in pregnancy.

Interactions

Monitoring & kinetics

Treat household; repeat at 1 week; hot-wash linen/clothing

Topical (whole body for scabies, including under nails; neck-down in adults, include scalp/face in infants).

Source: NICE CKS — Scabies / head lice · BNF — Skin parasiticides