Antifungals Part 2: Echinocandins & Others
If ergosterol is a target fungi share partly with us, is there anything a fungus has that we truly lack? Yes — a cell wall, just like bacteria. The newest antifungals exploit that, delivering safe, powerful treatment for the most common serious fungal infections. And a handful of other clever drugs finish the toolkit, from the pill that cures athlete's foot to the one that treats fungal meningitis by sneaking into the fungus's own DNA.
A hospitalized patient develops a bloodstream infection with Candida — a serious fungal infection that used to mean reaching for the harsh amphotericin B. Instead the team starts an echinocandin, and the patient improves with remarkably few side effects. What changed? These newer drugs finally attack something a fungus has and we don't: its cell wall. Building on that breakthrough, and rounding out the antifungal toolkit, is the rest of this story — the drugs beyond the polyenes and azoles.
Echinocandins: attacking the wall
Fungi, like bacteria, have a cell wall — and we don't. The echinocandins — caspofungin, micafungin, anidulafungin — block the synthesis of β-glucan, a key building block of the fungal cell wall. Since human cells have no wall at all, this target is genuinely absent in us, which makes echinocandins among the SAFEST antifungals with few serious side effects — a welcome contrast to amphotericin. They are fungicidal against Candida (they've become a first-line choice for serious Candida bloodstream infections) and active against Aspergillus, though they don't cover every fungus and are given intravenously. In essence, they do for fungi what the β-lactams do for bacteria: exploit the one structure the pathogen has and the host lacks.
The rest of the toolkit
A few more drugs complete the picture, each with a distinct job. Terbinafine blocks an earlier step of ergosterol synthesis and concentrates in skin and nails — making it the oral drug of choice for stubborn fungal nail and skin infections like athlete's foot. Flucytosine is unusual: it's taken up by fungi and converted into a false building block that jams their DNA and RNA — but resistance develops quickly if it's used alone, so it's paired with amphotericin B, classically for cryptococcal meningitis. Griseofulvin, an older drug, deposits in keratin and treats stubborn skin and hair fungal infections (ringworm). And the topical azoles (clotrimazole, miconazole) and nystatin handle the everyday surface infections — thrush, athlete's foot, vaginal candida — acting right where they're applied. Together these round out a field defined by one hard truth: fungi are a lot like us, so hitting them precisely is a real achievement.
- Echinocandins (caspofungin) block β-glucan cell-wall synthesis — a target absent in humans → very safe.
- Echinocandins are first-line for serious Candida bloodstream infections; active vs Aspergillus; IV only.
- Terbinafine (ergosterol synthesis) concentrates in nails/skin → onychomycosis, tinea.
- Flucytosine jams fungal DNA/RNA; paired with amphotericin for cryptococcal meningitis.
- Topical azoles (clotrimazole) & nystatin treat everyday surface infections (thrush, tinea).
The echinocandins are the antifungal echo of the β-lactams. Just as penicillins are so safe because human cells have no cell wall to attack, echinocandins are safe because our cells have no β-glucan wall either — the target simply doesn't exist in us. It's the same principle of selective toxicity, applied to a different pathogen: find a structure the microbe absolutely must have and we absolutely lack, and you get a powerful drug with little to no harm to the host.
- Using flucytosine alone. Resistance develops fast — pair it (usually with amphotericin).
- Expecting a topical antifungal to cure a deep or systemic infection. It only acts on the surface.
- Forgetting echinocandins are IV only and don't cover every fungus.
- Using a short course for nail fungus. Terbinafine needs weeks-to-months as the nail grows out.
Why are echinocandins among the safest antifungals?
- Echinocandins block the β-glucan cell wall (absent in humans) → very safe; first-line for serious Candida.
- Terbinafine concentrates in nails/skin → nail and skin fungal infections.
- Flucytosine jams fungal DNA/RNA — paired with amphotericin (cryptococcal meningitis).
- Topical azoles & nystatin treat everyday surface infections (thrush, tinea, vaginal candida).
- Katzung BG. Basic & Clinical Pharmacology — Antifungal Agents (echinocandins, terbinafine, flucytosine).
- Brunton LL, et al. Goodman & Gilman's The Pharmacological Basis of Therapeutics — Antifungal agents.
- Rang HP, Dale MM, et al. Rang & Dale's Pharmacology — Antifungal drugs.
- IDSA guidelines — Candidiasis & cryptococcal disease treatment (echinocandins, flucytosine).
- Whalen K. Lippincott Illustrated Reviews: Pharmacology — Antifungal drugs.
