Amphotericin B – Uses, Mechanism & Side Effects
Amphotericin B is an antifungal medication used to treat severe and life-threatening fungal infections. It is one of the most potent antifungals available and is typically reserved for serious systemic infections.
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Amphotericin B is an antifungal medication used to treat severe and life-threatening fungal infections. It is one of the most potent antifungals available and is typically reserved for serious systemic infections.
What is Amphotericin B?
Amphotericin B is an antifungal medication belonging to the polyene class of drugs. It has been used in clinical medicine since the late 1950s and remains one of the most important treatments for severe, systemic fungal infections. The compound is derived from the soil bacterium Streptomyces nodosus and is active against a broad range of fungal pathogens as well as certain parasites.
Indications – When is Amphotericin B Used?
Amphotericin B is primarily used for severe, life-threatening fungal infections that cannot be adequately treated with other antifungal agents. Common indications include:
- Invasive aspergillosis (mold infection, particularly in immunocompromised patients)
- Cryptococcal meningitis (fungal infection of the brain and its surrounding membranes)
- Invasive candidiasis (systemic yeast infection)
- Histoplasmosis, coccidioidomycosis, blastomycosis (rare endemic fungal infections)
- Mucormycosis (life-threatening mold infection)
- Visceral leishmaniasis (parasitic disease, treated with the liposomal form)
It is most commonly used in patients with weakened immune systems, such as those who have undergone organ transplantation, are living with HIV, or are receiving chemotherapy.
Mechanism of Action
Amphotericin B works by binding to ergosterol, a key component of the fungal cell membrane. This binding creates pores (tiny holes) in the membrane, causing an uncontrolled leakage of potassium and other ions out of the fungal cell. This disrupts cellular metabolism and ultimately leads to cell death, making Amphotericin B a fungicidal (fungus-killing) agent. Because human cell membranes contain cholesterol rather than ergosterol, the drug acts selectively against fungi. However, at higher concentrations, it can also interact with cholesterol, which partly explains its side effect profile.
Formulations and Dosage
Amphotericin B is available in several formulations that differ in tolerability and clinical application:
- Conventional Amphotericin B (deoxycholate formulation): The original form, administered intravenously. Highly effective but associated with significant side effects.
- Liposomal Amphotericin B (L-AmB): The active ingredient is encapsulated in liposomes (small lipid spheres). This formulation is much better tolerated and is now the preferred option in most clinical settings.
- Amphotericin B lipid complex (ABLC): Another lipid-based formulation with improved tolerability compared to the conventional form.
Dosage is determined individually by the treating physician and depends on the type and severity of the infection, the patient's body weight, and kidney function. Amphotericin B is administered exclusively under medical supervision in a hospital setting.
Side Effects
Amphotericin B is well known for its significant side effects, which is why it is used as a last-resort or reserve agent under strict medical monitoring:
Common Side Effects
- Fever, chills, and nausea during infusion (infusion-related reactions)
- Headache and muscle pain
- Changes in blood pressure (increase or decrease)
Serious Side Effects
- Nephrotoxicity (kidney damage): The most clinically significant side effect. Regular monitoring of kidney function is essential during treatment.
- Electrolyte imbalances: Particularly low potassium (hypokalemia) and low magnesium levels
- Anemia (reduced production of red blood cells)
- Elevated liver enzyme levels
Liposomal formulations are associated with significantly fewer side effects, especially reduced kidney toxicity, and are therefore the preferred choice when available.
Drug Interactions
Amphotericin B can interact with various other medications. Key interactions include:
- Nephrotoxic drugs (e.g., aminoglycosides, ciclosporin): Increased risk of kidney damage
- Corticosteroids: May worsen potassium depletion
- Cardiac glycosides (e.g., digoxin): Increased risk of toxicity due to low potassium levels
- Antidiabetic medications: Possible effects on blood glucose levels
Resistance
Resistance to Amphotericin B is uncommon but does occur. It typically develops through alterations in the ergosterol biosynthesis pathway of the fungus. Because resistance poses a serious clinical challenge, the use of Amphotericin B is reserved for severe infections to minimize the risk of resistance development.
References
- World Health Organization (WHO): WHO Model List of Essential Medicines, 23rd Edition, 2023.
- Pappas PG, Rex JH, Sobel JD et al.: Guidelines for Treatment of Candidiasis. Clinical Infectious Diseases, 2004; 38(2): 161-189.
- Brunton LL, Knollmann BC (eds.): Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th Edition. McGraw-Hill Education, 2022.
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