Questions and Answers
What are the three general types of chemotherapies against fungal infections?
What are the three major antifungal drug classes?
Polyene antibiotics, azoles, echinocandins
What are the three polyene antibiotics?
Amphotericin B, nystatin, natamycin
What is the mechanism of action of amphotericin B?
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How is amphotericin B administered?
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What is the therapeutic use of amphotericin B?
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What are the adverse effects of amphotericin B?
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What are nystatin and natamycin used for?
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What are the two subclasses of azole drugs?
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Study Notes
Antifungal Drugs Overview
- Antifungal therapies are divided into categories based on their administration route: oral/parenteral for systemic infections, oral for skin/mucous membranes, and topical for localized infections.
Major Antifungal Drug Classes
- Polyene Antibiotics: Bind to ergosterol; key example is amphotericin B.
- Azoles: Target the P450 enzyme involved in ergosterol synthesis; include two subclasses of drugs.
- Echinocandins: Inhibit fungal cell wall biosynthesis; also includes flucytosine, terbinafine, and griseofulvin.
Polyene Antibiotics
- Key Examples: Amphotericin B is the most critical, followed by nystatin and natamycin.
Amphotericin B Details
- Primary treatment for systemic mycoses, especially in immunocompromised patients; increasingly being replaced by newer drugs.
- Chemical structure: One side is highly polar with multiple hydroxyl groups; the other side is largely non-polar due to unsaturated double bonds.
Mechanism of Action of Amphotericin B
- Functions as a fungicide by causing cell leakage; resistant cells have lower ergosterol levels.
- Higher binding affinity to ergosterol than cholesterol, forming aqueous channels in fungal membranes that lead to cell death.
Pharmacokinetics of Amphotericin B
- Administered via IV; poorly absorbed in the gastrointestinal tract.
- High volume of distribution indicates extensive tissue binding; significant serum protein binding.
- Does not cross the blood-brain barrier easily, necessitating intrathecal administration for CNS infections.
- Slow elimination via metabolism with a half-life of 2-3 weeks.
Adverse Effects of Amphotericin B
- High therapeutic index implies potential toxicity; therapeutic index defined as TI = LD50/ED50.
- Common adverse effect: azotemia, an elevation of nitrogenous waste products in the blood.
Administration Methods
- Amphotericin B is primarily given through IV routes; intrathecal methods may be required for certain infections.
Therapeutic Use of Amphotericin B
- Considered the gold standard for invasive mycoses, effective against a wide range of fungi, including C. albicans and Aspergillus fumigatus.
- Administration ranges from 0.3 to 1.5 mg/kg/day for a total of 1-2 grams; switching to lipid form or triazoles may occur to mitigate kidney toxicity.
- Often used for initial "induction" therapy before transitioning to less toxic long-term treatments.
Nystatin and Natamycin
- Nystatin: Previously common treatment for skin and mucosal candidiasis; mostly replaced by fluconazole or echinocandins.
- Natamycin: Long-term food additive to prevent mold growth; used for specific ophthalmic fungal infections.
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Explore essential antifungal drugs and their classifications through these flashcards. Learn the different types of chemotherapy used against fungal infections and gain insight into the major drug classes and their mechanisms. Perfect for students and healthcare professionals alike!
