Synthetic Pyrethroid (Antiparasitic)

Permethrin

Brand names: Lyclear (5% cream)

Permethrin is a topical insecticide used for scabies and head lice.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Directions Inspect • all household members should be checked by another person for lice and/or nits (eggs) • use a magnifying glass in bright light to help you see the lice and nits (eggs) • use a tool, such as a comb or two unsharpened pencils to lift and part the hair • look for tiny nits near the scalp, beginning at the back of the neck and behind the ears • small sections of hair (1-2 inches wide) should be examined at a time • unlike dandruff, nits stick to the hair. Dandruff should move when lightly touched. • if either lice or nits (eggs) are found, treat with the creme rinse Treat • wash hair with a shampoo without conditioner. Do not use a shampoo that contains a conditioner or a …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2022-11-21. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It is a synthetic pyrethroid that disrupts sodium channel function in the parasite's nerve membranes, causing paralysis and death of mites and lice.

Prescribing in practice

For scabies, treat all close physical and household contacts at the same time, whether or not they have symptoms, to prevent reinfestation.
For scabies, apply to the whole body including the neck, face where affected in older adults, and under the fingernails and toenails, washing off after the period specified in the SPC and usually repeating the application.
Persistent itching can continue for several weeks after successful treatment and does not by itself indicate failure or the need to re-treat.

Monitoring

No laboratory monitoring is required; review if itching is worsening rather than gradually settling, or if new burrows or lesions appear after treatment, which may suggest reinfestation or treatment failure.

Counselling the patient

Treat all close contacts and household members on the same day, even those without symptoms.
For scabies, apply to the whole body as directed, including under the nails, and reapply after laundering hands if they are washed during the treatment period.
Itching may last for some weeks after the mites are cleared and usually settles; seek review if it is getting worse or new spots appear.

Evidence & guidelines

First-line topical treatment for scabies (NICE CKS scabies).

Reference: NICE NG225; PHE Scabies Guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Pathways