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 Adler-Moore et al. Med Mycol. 2016;3:1:223-231 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

Newer amphotericin B formulations 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

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 First-line indications Other 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: 0.7-1mg/kg/day Paediatrics: 0.7-1mg/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 Very common ( ≥1/10) Common (≥1/100 to <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. J Antimicrob Chemother. 1994; 33: 203-213 Khoo et al.

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