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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Other antifungals

Antifungals with their own targets: terbinafine (squalene epoxidase), flucytosine (fungal DNA and RNA) and griseofulvin (microtubules).

Updated 2026-11-01

## What they are

A group of unrelated drugs. Terbinafine and griseofulvin are oral drugs for dermatophytes (nails, scalp, skin); flucytosine is given with amphotericin B for cryptococcal meningitis and serious Candida infections.

## Mechanism of action

Terbinafine blocks squalene epoxidase, an early step of ergosterol synthesis, so toxic squalene builds up (fungicidal). Flucytosine enters the fungus, is turned into fluorouracil and corrupts fungal RNA and DNA synthesis. Griseofulvin binds microtubule proteins and stops fungal mitosis; it concentrates in new keratin.

Target: Different targets: squalene epoxidase, nucleic acid synthesis, microtubules

## Key points

- Terbinafine: oral drug for onychomycosis; can cause liver failure and loss of taste or smell.
- Flucytosine never alone (resistance appears fast): it is combined with amphotericin B; it suppresses the bone marrow.
- Flucytosine is selective because human cells lack cytosine deaminase.
- Griseofulvin induces CYP enzymes (less warfarin and contraceptive effect), is contraindicated in pregnancy and porphyria and can cause a disulfiram-like reaction with alcohol.

## Drugs in this class

- [**Terbinafine** Allylamine antifungal for nail and skin fungus (dermatophytes). It blocks squalene epoxidase; rare liver failure and… Fungal squalene epoxidase (ERG1)](https://durgical.com/en/pharmacology/terbinafine/)
- [**Flucytosine** Oral antifungal turned into fluorouracil inside the fungus. Given with amphotericin B for cryptococcal meningitis; it… Fungal RNA and thymidylate synthase, through its metabolite fluorouracil](https://durgical.com/en/pharmacology/flucytosine/)
- [**Griseofulvin** Oral antifungal for dermatophytes of skin, hair and nails, classic for tinea capitis in children. It binds… Fungal microtubules (tubulin)](https://durgical.com/en/pharmacology/griseofulvin/)

## Others in the class

- ciclopirox (topical)
- ibrexafungerp

## Test yourself

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

## Why is terbinafine fungicidal while most azoles are fungistatic against Candida?

Blocking squalene epoxidase not only removes ergosterol but also makes squalene pile up to toxic levels that make the membrane leaky.

## Which human enzyme deficiency makes flucytosine dangerous?

Dihydropyrimidine dehydrogenase (DPD) deficiency: fluorouracil from flucytosine is not broken down, causing severe toxicity; complete deficiency is a contraindication.

## Why does griseofulvin cure tinea capitis only slowly?

It binds to newly formed keratin and protects it, so the infected hair or skin must grow out and be replaced.

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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); [DailyMed - FLUCYTOSINE capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5721b46a-4a9f-46c2-8804-a9bad4d5f80a) (DailyMed (U.S. National Library of Medicine), 2025); [DailyMed - GRISEOFULVIN MICROSIZE- griseofulvin tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1c26d7a6-17d9-4a95-a4ee-cfc5fe6bb95d) (DailyMed (U.S. National Library of Medicine), 2025); 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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