1. Amphotericin B Dr Pippa Newton, Infectious Diseases Consultant,
Manchester University NHS Foundation Trust

2. Intended learning outcome
To understand the mechanism of action of amphotericin B
To be aware of the spectrum of activity of amphotericin B
To understand the pharmacokinetics of amphotericin B
To be aware of the clinical indication and dosages of amphotericin B
To be aware of the adverse events associated with amphotericin B therapy

3. Introduction
Amphoterin B, the first systemic antifungal, was introduced in 1958
It’s a natural product from the actinomycete Streptomyces nodosus
It offers potent, broad-spectrum antifungal activity against yeasts, moulds and the dimorphic fungi
It’s a large molecule with both hydrophobic and hydrophilic portions (amphiphatic)
It has a molecular weight of 924 g/mol

4. Structure of amphotericin B
Chemical properties
Amphoteric
Reacts as an acid as well as a base
Polyene
Many double bonds
Macrolide
Contains large lactone ring
Lactone
Multiple ketone and hydroxyl groups

5. Mechanism of action
Amphotericin B binds fungal membrane ergosterol causing:
Increased membrane permeability and
Creation of transmembrane channels (pores)
Resulting in:
Leakage of monovalent ions (K+, Na+, H+, and Cl-),
Leakage of macromolecules from fungal cell
Other mechanisms
Stimulates fungus to produce oxygen radicles
Modulation of macrophage activity
Stimulates pro-inflammatory cytokines
Reactive oxygen intermediates
Nitric oxide
Eventually cell death
Adler-Moore et al. Med Mycol. 2016;3:1:

6. Amphotericin B formulations
“Conventional”
Amphotericin B deoxycholate (AmB-d)
Newer (lipid-based) formulations
Liposomal amphotericin B (L-AmB)
Amphotericin B lipid complex (ABLC)
Amphotericin B colloidal dispersion (ABCD)
Many others

7. Newer amphotericin B formulations
Advantages:
Fewer side effects: lipid vehicle acts as reservoirs, reducing binding to human cells
Improved tolerability
Altered tissue penetration – more in liver, spleen and brain, less in lung and kidneys
Reduced toxicity (esp. nephrotoxicity and anaemia)
However, compared to AmB-D these formulations are less potent by mg dose
Macrophage
Liposome
Lysosome
Fusion
Liposome
degradation
Endocytosis
Endocytic
vesicle
Release from
macrophage
Release in blood
compartment

8. Spectrum of activity
Amphotericin B is one of the most potent antifungal agents, demonstrating activity against:
Moulds
Yeasts
Dimorphic fungi

9. Spectrum of activity of Amphotericin B compared to triazoles
Fungi
Amphotericin B
Fluconazole
Itraconazole
Voriconazole
Posaconazole
Candida albicans
+++
Candida lusitaniae -
Candida krusei
+/-
Cryptococcus spp ++
Aspergillus fumigatus
Aspergillus terreus
Blastomyces spp +
Coccidioides spp
Histoplasma spp
Sporothrix spp
Chromoblastomycoses
Fusarium spp
Scedosporium spp
Mucorales
Perfect JR Clin Infect Dis. 2010;50:
Pappas PG Clin Infect Dis 2009;48:

10. Resistance Higher MICs to: Intrinsic resistance Acquired resistance
Aspergillus terreus
Aspergillus nidulans
Candida lusitaniae
Scedosporium spp.
Acquired resistance
Very rare
Higher MICs to:
Aspergillus flavus
Fusarium spp.
Scedosporium spp.
Candida krusei
Paecilomyces lilanicus

11. Resistance Higher MICs Intrinsic resistance Aspergillus flavus
Fusarium spp.
Scedosporium spp.
Candida krusei
Paecilomyces lilanicus
Aspergillus terreus
Aspergillus nidulans
Candida lusitaniae
Scedosporium spp.
Acquired resistance
Very rare

12. Biopharmaceutical differences of amphotericin B formulations
Characteristics
AmB-d
L-AmB
ABLC
ABCD
Mol % AmB
34%
10%
35%
50%
Lipid configuration
Micelles
Small unilamellar vesicles
Ribbon-Like
Disk like
Diameter (µm)
<0.4
0.08
Dosage (mg/kg)
0.5-1
3-5 5
3-4
Cmax (vs. AmB-d) -
Increased
Decreased
AUC (vs. AmB-d)
Vd (vs. AmB-d)
Similar
Clearance (vs. AmB-d)
Nephrotoxicity
+++
+/-
Infusion toxicity
High
Mild
Moderate
Groll et al . Adv. Pharmacol. 1998;44:

13. Lipid Amphotericin B formulations

14. Pharmacokinetics Bioavailability: All formulations are parental
Distribution: Well distributed in most body compartments
CNS penetration ~0%
Metabolism: t1/2: ~15 days (detectable in urine for at least 7 weeks after last dose)
Protein binging > 90% and is poorly dialyzable
Elimination: Excreted unchanged in urine (21%) and faeces (43%)
Bellmann & Smuszkiewicz: Infections pp1-43

15. Clinical indications Other indications First-line indications
Cryptococcal meningitis
Histoplasmosis
Mucormycosis
Penicilliosis (Talaromyces marneffei infection)
Leishmaniasis
Other indications
Invasive aspergillosis
Invasive candidiasis
Candidaemia
Coccidioidomycosis
Blastomycosis
Phaeohyphomycosis
Sporotrichosis (disseminated)
Oesophageal candidiasis
Nett & Andes. Infect Dis Clin N Am. 2016;
Indications in red are the main first line indications where amphotericin B is the leading product.

16. Dosages Amphotericin B deoxycholate Amphotericin B Liposomal Adults:
Adults: mg/kg/day
Paediatrics: mg/kg/day
Amphotericin B Liposomal
Adults:
Empiric therapy in neutropenia: 3 mg/kg/day
Systemic infections: 3-5 mg/kg/day
Cryptococcal meningitis: 6 mg/kg/day
Paediatrics: same weight-based dosing

17. Adverse events Acute infusion-related reactions Nephrotoxicity
Nausea, vomiting, rigors , fever, hyper/hypotension, and hypoxia
Caused by the effects of amphotericin B on pro-inflammatory cytokine production
Nephrotoxicity
34-60% of patients
Due to:
Vasoconstriction
Direct damage to the distal tubule cell membranes
Results:
Loss of electrolytes
Impaired urinary acidification and concentration
Renal tubular acidosis
Loo et al. Expert Opin Drug Saf. 2013;12:
Groll et al. Adv Pharmacol. 1998; 44;

18. Other adverse events Common (≥1/100 to <1/10) Very common ( ≥1/10)
Nausea, vomiting
Hypotension
Hypokalaemia
Transient renal function test abnormalities (azotemia, hyposthenuria, renal tubular acidosis and nephrocalcinosis)
Chills
Common (≥1/100 to <1/10)
Anaemia
Hypomagnesemia
Headache
Diarrhoea
Liver function test abnormalities
Injection site pain (with or without phlebitis or thrombophlebitis)
Acute renal failure
Bone or other pain (AmBisome)
Rare ( ~ 1/1000)
Anaphylaxis
Fungizone SPC: emc last updated 29-Nov-2016

19. Contraindication Known hypersensitivity to amphotericin B
Unstable/moderately renal dysfunction, unless unavoidable.

20. Tips on administering amphotericin B
Use a central line if possible for AmB-D, as phlebitis common – not so important for lipid-AmB.
Set the infusion up and run in about 10 ml, and then stop for mins to check for anaphylaxis – a ‘test dose’ unnecessary and delays therapy.
Slower infusions reduce acute infusion-related side effects (> 2 hours for lipid formulations, > 4 hours for AmB-d)
Pre-loading with N/saline (500-1,000 mL) reduces renal dysfunction
Check renal function daily for first 4-5 days then, 3x weekly
Avoid other nephrotoxic drugs, especially aminoglycosides and frusemide
Check K+ at least 2x/week and mg++ weekly, if possible.
Amiloride 5 mg daily, may reduce K+ loss.
Check Hb at 7, 14 and 21 days – may need transfusion
Avoid giving hydrocortisone for infusion-related side effects, if possible. Use acetaminophen/paracetamol, or low dose opiate.
Khoo et al.
Khoo et al. J Antimicrob Chemother. 1994; 33:

21. Conclusion
Amphoterin B, the first systemic antifungal, was introduced in 1958
It offers potent, broad-spectrum antifungal activity but is associated with significant renal toxicity and infusion reactions
Lipid-based amphotericin B formulations were introduced in the 1990s and maintain the potent, broad-spectrum activity of the deoxycholate formulation with less toxicity
Drug of choice for the vast majority of life-threatening systemic fungal infections
Treatment of mycoses in pregnant women as triazole class are considered teratogenic