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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Onychomycosis and nail sampling

Dermatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull

Synopsis

Distinguish fungal nail disease from common dystrophic mimics, collect representative keratin before systemic treatment, and prescribe topical or oral antifungal therapy with liver and interaction safeguards.

  • Onychomycosis commonly produces distal or lateral yellow-white discolouration, subungual debris, thickening, brittleness and onycholysis, but psoriasis and trauma can look identical.
  • Examine every nail plus toe webs, soles, palms and scalp; untreated tinea pedis can repeatedly reseed a treated toenail.
  • Before oral therapy, clean away surface contaminants, clip back to the most proximal diseased nail possible and include subungual debris for microscopy and culture or the local validated molecular pathway.
  • A negative result after a small distal clipping or recent antifungal use does not exclude infection; repeat a technically better sample when suspicion remains and treatment would be consequential.
Limited distal disease without matrix involvement can be treated with amorolfine 5% lacquer once weekly, usually for six months on fingernails and nine to twelve months on toenails.
  • For confirmed dermatophyte disease needing systemic treatment, terbinafine 250 mg orally once daily is commonly used for six weeks for fingernails and twelve weeks for toenails.
  • Check liver disease, baseline liver function, pregnancy, interactions and the exact product information before oral terbinafine; repeat liver tests after four to six weeks under the SmPC.
  • Clinical cure lags microbiological cure because clear nail must grow from the matrix. Toenails may take twelve to eighteen months to look normal even after fungus is eradicated.
  • Treat shoes, moisture and coexisting foot fungus pragmatically, but do not expose every cosmetically dystrophic nail to systemic medicine when benefit is small or diagnosis unconfirmed.

    • Key red flags

    A new irregular pigmented nail band, periungual pigment, ulceration, bleeding or a nail-bed mass requires urgent melanoma assessment; painful spreading erythema, diabetic foot ulceration, ischaemia or systemic infection needs prompt acute foot or infection care.

    Pigmented-lesion warning

    A new irregular longitudinal band, Hutchinson pigment, nail destruction, bleeding or a mass is not assumed fungal and needs urgent lesion assessment.

    Investigation priorities

    01
    Representative nail clipping and subungual debrisFirst step

    Obtain active infected keratin for laboratory confirmation before systemic treatment.

    Management branches

    ConfirmSample before systemic exposure

    Nail dystrophy is uncertain or oral antifungal treatment is being considered.

    1. Stop cosmetic polish, clean the plate and examine all nails, skin and feet for psoriasis, trauma, tinea and a suspicious pigmented or destructive lesion.
    2. Clip the most proximal accessible diseased plate and collect generous subungual material, sending the exact site and treatment history for microscopy and culture or local PCR.
    3. If a weak sample is negative but clinical probability remains high, repeat from a better active site before declaring resistance or prescribing months of systemic therapy.

    Key medicines

    Terbinafine 250 mg tabletsTake 250 mg by mouth once daily for six weeks for fingernail infection and twelve weeks for toenail infection unless specialist advice changes duration.Contraindicated in chronic or active hepatic disease. Check baseline liver function and repeat after four to six weeks; stop for anorexia, nausea, fatigue, right-upper-quadrant pain, jaundice, dark urine or pale stool, and review CYP2D6 interactions, rash, taste, smell and blood dyscrasia symptoms.
    Amorolfine 5% medicated nail lacquerApply to affected nails once weekly after filing and cleaning, continuing about six months for fingernails and nine to twelve months for toenails until healthy nail has regrown.Avoid skin, eyes and mucosa, use dedicated files and do not use cosmetic artificial nails over treatment. Extensive, matrix or painful disease and diabetes or poor circulation require clinician review rather than self-treatment.
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    Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
    Sources

    Sources and review status

    National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

    • British Association of Dermatologists fungal nail infectionsClinical features, confirmation, treatment choices and regrowth expectations.
    • NHS fungal nail infectionRecognition, self-care, treatment and referral advice.
    • Lamisil tablets 250 mg SmPCLicensed dose, nail durations, hepatic monitoring and adverse-effect precautions.
    • Amorolfine 5% nail lacquer SmPCLicensed weekly topical regimen, duration and limits of self-treatment.

    Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

    Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom