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

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

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

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

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;3:1:223-231

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

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

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

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;50:291-322. Pappas PG Clin Infect Dis 2009;48:503-535.

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

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

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 1.6-11.0 0.12-0.14 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;44:343-500

Lipid Amphotericin B formulations

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. 2017.pp1-43

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; 30 51-83 Indications in red are the main first line indications where amphotericin B is the leading product.

Dosages Amphotericin B deoxycholate Amphotericin B Liposomal Adults: Adults: 0.7-1 mg/kg/day Paediatrics: 0.7-1 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

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: 881-895 Groll et al. Adv Pharmacol. 1998; 44;343-500

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

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

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 15-20 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: 203-213

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