Derbac-M

What is Derbac-M?

Derbac-M Liquid is a topical insecticide containing malathion 0.5%, supplied as a white, creamy liquid emulsion. It's licensed in the UK for the eradication of head lice, pubic lice (crab lice) and their eggs, and for the treatment of scabies in adults, the elderly and children aged 6 months and over. Because it's alcohol-free, it may be more suitable for people with asthma or eczema than some alternative treatments. This page focuses specifically on using Derbac-M for pubic lice; the application method differs from head lice treatment, so it's important not to follow head lice instructions by mistake.

What are pubic lice (crabs)?

Pubic lice, sometimes called crabs, are small insects that live in coarse body hair, most commonly pubic hair but also hair on the chest, abdomen, thighs, armpits, and occasionally beards, moustaches, eyebrows or eyelashes. They don't affect the hair on your head. Signs include itching (often worse at night), tiny grey-brown lice around 2mm long, and small dark specks (their eggs) attached to hairs close to the skin.

Pubic lice spread through close body contact, most often sexual contact, though they can occasionally spread via shared bedding or towels used shortly beforehand. Because transmission happens through skin-to-skin and hair contact rather than fluid exchange, condoms don't fully prevent spread. Having pubic lice isn't a sign of poor hygiene; anyone can get them through close contact.

How Derbac-M is used for pubic lice

The instructions below are specific to pubic lice and are different from the head lice directions on the same product.

• Apply Derbac-M to the entire skin surface, paying particular attention to all hairy areas, including the beard and moustache if affected.
• Avoid applying to any other areas above the neck, including the scalp and face.
• Leave the liquid on for at least one hour before washing off, though the leaflet advises leaving it on overnight where possible for the best result.
• Wash off in the usual manner.
• Repeat the treatment after 7 days, even if you feel the lice have gone, as this second application targets any eggs that have since hatched.

Check other members of your household or close contacts for live lice and treat them too if needed. Itching and any rash can take up to a week to settle after treatment clears the infestation; a soothing cream can help in the meantime. A single correctly-timed application doesn't guarantee every egg is destroyed, which is why the repeat treatment at 7 days matters. If lice are still present after completing both applications, this may reflect reinfestation from an untreated contact or a gap in how the product was applied, rather than the treatment failing outright, and it's worth speaking to a clinician either way.

When Derbac-M shouldn't be used

• Never apply Derbac-M to the eyelashes, eyebrows, or near the eyes. If pubic lice affect the eyelashes, this needs specialist management at a sexual health clinic rather than self-treatment with Derbac-M, as the standard product isn't licensed or suitable for use around the eyes.
• Don't use on broken or secondarily infected skin.
• Don't use on infants under 6 months unless a clinician has specifically advised it.
• Avoid prolonged or repeated use beyond what's directed: the product shouldn't be used more than once a week, and not for more than 3 consecutive weeks.
• If you have sensitive skin, it's worth testing a small area first. If you have asthma, speak to a clinician before use.
• If you're pregnant, breastfeeding, or think you might be pregnant, get advice from a clinician before using Derbac-M.
• If lice persist despite correct use and repeat treatment, or if you're not sure the diagnosis is right, see a sexual health clinician for assessment.

Treating partners and close contacts

Current and recent sexual or close contacts should also be checked and treated where appropriate, in line with UK sexual health guidance. Avoid sexual and close body contact until you and your partner(s) have both completed treatment, to prevent passing lice back and forth.

Laundry and household hygiene

Wash clothing, bedding and towels used recently on a hot wash of 50°C or above, as this temperature kills lice and eggs. Items that can't be machine washed can be dry-cleaned or sealed in a plastic bag for at least a week to a fortnight, which allows any remaining lice to die off naturally. Vacuuming the mattress can help, and it's sensible to avoid sharing towels or clothing while treating an infestation. Insecticide sprays aren't recommended for use around the home; they're not necessary and can be irritating.

Side effects and safety

Like all medicines, Derbac-M can cause side effects, though not everyone experiences them.

Reported effects include skin irritation and allergic reactions, some of which can be severe and involve difficulty breathing, dizziness, or swelling of the face, throat or eyes. Chemical burns have also been reported.

Derbac-M is for use on the skin only. Protect the eyes with a towel during application. If the liquid gets into the eyes, wash out immediately with plenty of water. If it's swallowed accidentally, contact a doctor or hospital straight away.

Because pubic lice are usually acquired through sexual contact, an STI screen is also worth considering, even though the lice themselves are ectoparasites rather than a sexually transmitted infection in the conventional sense. Testing helps rule out anything else that may have been passed on at the same time.

How to get Derbac-M through DoktorABC

To access Derbac-M through DoktorABC, complete a short online consultation. A UK-registered prescriber will review your answers and, where appropriate, approve treatment, which is then dispensed by a GPhC-registered pharmacy and delivered to your door in discreet packaging.