Pharmacology · Antifungal Agents

Echinocandins — Caspofungin, Micafungin & Anidulafungin

Glucan synthase inhibition, class advantages, agent differences, and FKS resistance

Echinocandins target β-1,3-glucan synthase — an enzyme unique to fungi with no mammalian homolog — producing a cell wall defect that causes osmotic fragility and cell lysis; this selectivity explains their excellent safety profile with minimal mammalian toxicity.
Echinocandins are the preferred first-line agents for invasive candidiasis in most patients — superior to fluconazole for candidemia in clinical trials, with fungicidal activity against Candida, no significant CYP drug interactions, and excellent tolerability.
None of the three echinocandins is orally bioavailable — all require IV administration; once-daily dosing and no requirement for renal or hepatic dose adjustment (except caspofungin in severe hepatic impairment) make them operationally convenient for hospitalized patients.
Echinocandins have no reliable activity against Cryptococcus neoformans — the cryptococcal cell wall lacks meaningful β-1,3-glucan — or against Mucorales, dimorphic fungi, or Fusarium; spectrum is confined to Candida and Aspergillus.
FKS1/FKS2 hot-spot mutations in the glucan synthase gene confer echinocandin resistance — the same mutations produce cross-resistance to all three agents; emerging pan-echinocandin-resistant Candida auris and Candida glabrata are a significant clinical problem.

Abbreviations: β-1,3-glucan = beta-1,3-glucan · FKS = FKBP506 rapamycin target (glucan synthase gene) · MIC = minimum inhibitory concentration · CYP = cytochrome P450 · IV = intravenous · IA = invasive aspergillosis · ESBL = extended-spectrum beta-lactamase · MDR = multidrug-resistant · CrCl = creatinine clearance

Mechanism and Class Advantages

Target — β-1,3-Glucan Synthase

Fungal-Specific Cell Wall Disruption

β-1,3-glucan is the primary structural polysaccharide of the fungal cell wall — provides osmotic resistance
Echinocandins non-competitively inhibit the Fks1/Fks2 subunit of β-1,3-glucan synthase
Glucan depletion → cell wall fragility → osmotic lysis → fungicidal killing of Candida
Mammalian cells lack β-1,3-glucan entirely → no mammalian target → excellent intrinsic safety
Activity against Aspergillus: fungistatic (damages growing hyphal tips but does not lyse established mycelium)

Class Advantages vs. Azoles and Amphotericin B

Why Echinocandins Are First-Line for Candidemia

Fungicidal against Candida — not fungistatic like azoles
Minimal drug interactions — no CYP3A4 inhibition; few clinically significant interactions
Active against azole-resistant Candida (different mechanism — FKS vs. ERG11/efflux)
Active against Candida krusei and most Candida glabrata — intrinsically fluconazole-resistant species
Excellent safety profile — no nephrotoxicity, no hepatotoxicity at clinical doses, minimal infusion reactions
No renal adjustment required for any agent (caspofungin: reduce in severe hepatic impairment)

Caspofungin vs. Micafungin vs. Anidulafungin

Feature	Caspofungin	Micafungin	Anidulafungin
Loading Dose	70 mg IV × 1, then 50 mg daily	No loading dose — 100 mg daily (candidemia); 50 mg daily (esophageal)	200 mg IV × 1, then 100 mg daily
Elimination	Hepatic (non-CYP degradation); reduce maintenance to 35 mg daily in moderate/severe hepatic impairment	Hepatic; no dose adjustment in renal or mild-moderate hepatic impairment	Chemical degradation in plasma (non-enzymatic) — not hepatically or renally metabolized; no dose adjustment
Drug Interactions	Cyclosporine: ↑ caspofungin AUC ~35% — monitor LFTs; rifampin induces caspofungin metabolism → use 70 mg daily maintenance with rifampin	Sirolimus: ↑ sirolimus AUC ~21%; nifedipine: ↑ nifedipine AUC ~18% — monitor	Fewest interactions — chemical degradation avoids CYP-based interactions; cyclosporine ↑ anidulafungin AUC modestly
Approved Indications	Candidemia; esophageal/oropharyngeal candidiasis; IA (salvage); empiric therapy in febrile neutropenia	Candidemia and invasive candidiasis; esophageal candidiasis; prophylaxis in HSCT	Candidemia and invasive candidiasis; esophageal candidiasis
Special Note	First echinocandin approved; most clinical experience; FDA-approved for empiric therapy in neutropenic fever	Only echinocandin FDA-approved for prophylaxis in hematopoietic stem cell transplant recipients	Unique non-enzymatic degradation — preferred when hepatic dysfunction is severe or drug interactions concern

Spectrum and FKS Resistance

Coverage and Gaps

What Echinocandins Cover — and Don't

All Candida species including C. krusei, C. glabrata, and most C. auris — fungicidal
Aspergillus species — fungistatic; used in combination or step-down
Cryptococcus neoformans — intrinsically resistant; cell wall lacks sufficient β-1,3-glucan
Mucorales — intrinsically resistant; use amphotericin B
Fusarium, Scedosporium — not covered; use voriconazole
Endemic dimorphics (Histoplasma, Blastomyces) — not reliable; use azoles or amphotericin B

FKS Mutations — Echinocandin Resistance

Hot-Spot Mutations in Glucan Synthase

Point mutations in FKS1 (most Candida species) or FKS2 (C. glabrata) hot-spot regions HS1 and HS2 → glucan synthase no longer inhibited by echinocandins
Cross-resistant to all three echinocandins — class-wide resistance from a single mutation
FKS mutations in C. glabrata now detected in 10–15% of clinical isolates in some centers, especially after prior echinocandin exposure
Candida auris: FKS mutations increasingly detected — pan-echinocandin-resistant isolates reported globally
Susceptibility testing (CLSI or EUCAST) required for clinical failures; standard MIC breakpoints may miss heteroresistance

Positioning Rule: Echinocandin First, De-Escalate to Fluconazole

Start echinocandin therapy for all patients with suspected or confirmed invasive candidiasis — do not start with fluconazole empirically unless the patient is clinically stable, has no prior azole exposure, and species identification confirms fluconazole-susceptible Candida. The 2016 IDSA Candidiasis Guidelines explicitly recommend echinocandins as first-line for candidemia in all patient categories, with de-escalation to fluconazole permissible after 5–7 days once the patient is clinically stable and the isolate is confirmed susceptible.

De-escalation from echinocandin to fluconazole requires: (1) clinical stability and defervescence, (2) negative repeat blood cultures, (3) species identified as fluconazole-susceptible (not C. krusei, not C. glabrata with elevated MIC), and (4) no evidence of metastatic infection requiring prolonged therapy. Do not de-escalate to fluconazole if C. glabrata or C. auris is the causative organism unless susceptibility is confirmed.

Suggested References

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Katzung BG, ed.	Basic and Clinical Pharmacology, 15th ed. — Chapter 48: Antifungal Agents	McGraw-Hill, 2021
Brunton LL, Knollmann BC, eds.	Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. — Chapter 57: Antifungal Agents	McGraw-Hill, 2023
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