[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Other antifungals](https://durgical.com/en/pharmacology/classes/other-antifungals/) › Terbinafine

[Pharmacology](https://durgical.com/en/pharmacology/) · [Other antifungals](https://durgical.com/en/pharmacology/classes/other-antifungals/)

# Terbinafine

Allylamine antifungal for nail and skin fungus (dermatophytes). It blocks squalene epoxidase; rare liver failure and taste loss are its key risks.

Updated 2026-11-01

- Class: [Other antifungals](https://durgical.com/en/pharmacology/classes/other-antifungals/)
- Enzyme: Fungal squalene epoxidase (ERG1)
- ATC code: D01BA02
- WHO Model List of Essential Medicines

## Mechanism of action

Terbinafine inhibits squalene epoxidase, an early enzyme of ergosterol synthesis. Ergosterol falls and, above all, squalene accumulates to high concentrations that make the membrane permeable, so the fungus dies (fungicidal against dermatophytes).

- Terbinafine blocks fungal squalene epoxidase
- Squalene piles up and ergosterol is not made
- The membrane leaks and the dermatophyte dies

## Pharmacokinetics

**Absorption**
Well absorbed (over 70%), but first-pass metabolism leaves a bioavailability of about 40%; food has little effect.

**Distribution**
Over 99% bound to plasma proteins; it accumulates with repeated doses.

**Metabolism**
Liver; it inhibits CYP2D6.

**Onset and duration**
The nail looks cured only months after treatment, when healthy nail has grown out.

## Indications

- Onychomycosis of toenails or fingernails due to dermatophytes (tinea unguium), confirmed in the laboratory first. [Dermatophytosis (tinea) and onychomycosis →](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/)
- Tinea capitis (oral granules). [Dermatophytosis (tinea) and onychomycosis →](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/)

## Adverse effects

### Common

- Headache
- Diarrhoea, dyspepsia, nausea, abdominal pain and flatulence
- Rash and itching
- Raised liver enzymes
- Taste disturbance

### Serious (rare, important)

- Liver failure, sometimes leading to transplant or death
- Loss of taste or smell, which may be prolonged or permanent
- Depressive symptoms
- Severe neutropenia and other blood disorders
- Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS; lupus erythematosus

## Contraindications

- Chronic or active liver disease
- Hypersensitivity to terbinafine

## Key interactions

**Drugs metabolised by CYP2D6 (tricyclic antidepressants such as desipramine, SSRIs, beta-blockers, class 1C antiarrhythmics)**
Terbinafine inhibits CYP2D6 and raises their levels.

**Rifampicin**
Doubles terbinafine clearance (lower levels).

**Cimetidine and fluconazole**
Raise terbinafine levels.

**Warfarin**
Rises and falls of prothrombin time have been reported, without a proven causal link.

## What is monitored

- Liver tests before starting and periodically
- Blood count if signs of infection appear
- Taste, smell and mood

## Administration and safety

- Confirm onychomycosis with a nail sample (KOH, culture or biopsy) before oral treatment.
- Check for chronic or active liver disease and take baseline liver tests before the first dose.
- Tablets may be taken with or without food.

## Nursing care

- Teach the signs of liver injury (nausea, loss of appetite, tiredness, jaundice, dark urine, pale stools) and to stop and seek care if they appear.
- Ask about changes in taste or smell; they can lead to poor appetite, weight loss and low mood.
- Fever or sore throat may mean neutropenia: report promptly.
- Explain that the nail takes months to look normal after the course ends.

## Pregnancy and breastfeeding

Human data are insufficient and animal studies showed no harm; treatment of nail infections is usually postponed until after pregnancy.

## Memory aid

«TerbinaFINE for the nails, not FINE for the liver»: squalene builds up in the fungus, so it dies.

## Test yourself

Think of the answer, then tap the question to see it.

## Which enzyme does terbinafine inhibit, and what accumulates?

Squalene epoxidase; squalene accumulates to toxic levels in the fungal cell.

## What must be checked before starting oral terbinafine?

Laboratory confirmation of the fungal nail infection, and liver disease history with baseline liver tests.

## A patient on terbinafine says food tastes of nothing. What is the advice in the label?

Taste disturbance can be severe and permanent; the drug is stopped.

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## Related drugs

- [Griseofulvin](https://durgical.com/en/pharmacology/griseofulvin/)
- [Itraconazole](https://durgical.com/en/pharmacology/itraconazole/)

## Related conditions

- [Dermatophytosis (tinea) and onychomycosis](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/)

[← Back to the class: Other antifungals](https://durgical.com/en/pharmacology/classes/other-antifungals/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - TERBINAFINE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=18b16aad-1877-4b07-b532-f0ef4843af91) (DailyMed (U.S. National Library of Medicine), 2025); [Terbinafine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a699061.html) (MedlinePlus (U.S. National Library of Medicine), 2018); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 61 (McGraw Hill, 2023).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/terbinafine/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/terbinafine/