Core Microbiology - Anti-fungal Agents (5) Flashcards
Fungi classification
- Moulds/filamentous fungi
2. Yeast
Dimorphic fungi
Exist as mould and yeast
Erogsterol
In fungal cell membranes, forms clusters within phospholipid bilayer, regulates membrane permeability
Ergosterol biosynthesis
Squalene > (Squalene epoxidase) > Lanosterol > (Lanosterol 14a demethylase) > Ergosterol
B-1,3-glucans
Large polymers of UDP-glucose, form a fibrous network on inner surface of wall, snythesised by B-1,3-glucan synthase
Antifungal classes
Polyenes, Allylamines, Azoles, Echinocandins, others..
Polyenes mode of action
Association with ergosterol, forms pore-like molecular aggregates, loss of membrane integrity and leakage of K+, cell death
Examples of Polygenes
Amphotericin B and Nystatin
Amphotericin B spectrum of activity
Most fungi - Aspergillus, Candida, Cryptococcus (Parenterally)
Amphotericin B adverse effects
Allergic reactions, nephrotoxicity (reversible), not completely selective to fungi
Lipid associated Amphotericin B (AmB) different formulations
Liposomal AmB (L-AmB), AmB lipid complex (ABLC), AmB colloidal disperson (ABCD)
Lipid associated Amphotericin B (AmB) pros
Minimises delivery of AmB to kidney cells (liver, spleen and lymph nodes)
Nystatin
Too toxin for systemic use, superficial infections - oral/vaginal candidiasis
Allylamines mode of action
Inhibit erogsterol synthesis (Squalene epoxidase)
Allylamines examples
Terbinafine
Terbinafine spectrum
Broad in vitro
Terbinafine adverse effects
Liver toxicity (Jaundice, hepatitis)
Allylamines clinical use
Dermatophyte infections (superficial)
Topical - athletes foot (tinea pedis), tinea corporis (trunk, legs, arm/skin), tinea cruris (groin)
Systemic - scalp ringworm (tinea capitis), onychomycosis (nail)
Azoles
5-membered ring
Examples
- Imidazoles (2N)
- Triazoles (3N)
Azoles mode of action
Inhibit ergosterol synthesis (Lanosterol 14a-demethylase)
Azoles spectrum
Broad - yeasts and filamentous fungi (except Fluconazole/Aspergillus)
Imidazoles
Toxic, rarely used systemically (ketoconazole)
Examples of Imidazoles
Clotrimazole (Canesten), Miconazole, Ketoconazole
Examples of Triazoles
Fluconazole, Itraconazole, Voriconazole, Posaconazole, Isavuconazole
Azoles adverse effects
Hepatotoxicity
Azoles drug interactions
Inhibition of Cytochrome P-450 enzymes - increases concentration of all drugs metabolised by Cy P-450 enzymes
Imidazoles clinical use
Superficial infections - Candidiasis or dermatophyte infections
Triazoles clinical use
Systemic - aspergillosis and candidiasis
Echinocandins mode of action
Inhibition of B-1,3-glucan synthase, construction of severely abnormal cell wall
Examples of Echinocandins
Andiulafungin, Caspofungin, Micafungin
Echinocandins spectrum of activity
Aspergillus and Candida (not certain moulds and cryptococcus) - serious as iv
Echinocandins adverse effects
Skin rash, nausea, vomiting, headache, diarrhoea
5-fluorocytosine (5-FC)
Synthetic analogue of cytosine (pyrimidine nucleoside), developed as anti-cancer drug
5-FC mode of action
Entry into cells requires fungal cytosine permeases, converted to 5-fluorouracil and 5-fluorodeoxyuridine monophosphate (inhibit RNA/protein synthesis and DNA synthesis)
5-FC spectrum of activity
Yeasts only (Candida and Cryptococcus)
5-FC adverse effects
Bone marrow suppression, selective toxicity is incomplete - 5FU anti-cancer
5-FC clinical use
Cryptococcal meningitis (combination with AmB)
Griseofulvin mode of action
Inhibition of fungal mitosis
Griseofulvin spectrum of activity
Dermatophytes
Griseofulvin clinical use
Dermatophyte infections in children requiring system treatment (kerion, onychomycosis)
Antifungal drugs that require therapeutic drug monitoring
- Itraconazole
- 5-FC (bone marrow)
- Voriconazole (liver)