L37- Antifungals Flashcards
(57 cards)
(1) is the main target for anti-fungal agents
fungi have cell walls made out of (2)
1- ergosterol
2- chitin
-fungi resistant to anti-bacterials, bacteria resistant to anti-fungals
describe the classic classification of fungal infections
Opportunistic, immuno-compromised hosts:
- cancer chemotherapy
- following organ transplant
- HIV infection
Primary, immuno-competent hosts
describe the classification of fungal infections based on site of infections
Superficial mycoses: skin, mucous membranes, hair, nails
Subcutaneous mycoses: dermis, subcutaneous tissue, adjacent bone
Systemic mycoses: affects internal organs
______ are the main superficial mycoses
- dermatophytoses
- superficial form of candidiasis
(1) are the common causes of systemic mycoses and (2) is the biggest issue with these types of infections
1- (rarely occurs, worse than sepsis) candidiasis, cryptococcosis, aspergillosis
2- difficult to treat –> life-threatening
list the anti-fungals by MOA
1) alter cell permeability: Polyenes, Azoles, Allylamines
2) block nucleic acid synthesis: Anti-metabolites
3) disrupts microtubule function: Griseofulvin
4) disrupts fungal cell wall: Echinocandins
list the systemic drugs (for subcutaneous and system mycoses)
- amphotericin B (polyene)
- flucytosine (anti-metabolite)
- azoles
- echinocandins
describe the MOA of amphotericin B
(polyene)
- binds to ergosterol on fungal cell membrane
- forms pore in the cell membrane
- pores allow leakage of intracellular ions / macromolecules => cell death
Amphotericin B:
- fungi-(static/cidal)
- (broad/narrow) spectrum
- (3) is the main clinical use in general because of (4)
1- fungicidal
2- broad spectrum
3- life-threatening mycoses – including pregnancy
4- very toxic
Amphotericin B, describe routes of administration
IV mainly, poor oral F as its highly insoluble (deoxycholate colloidal suspension)
Intrathecal administration in meningeal disease (only way to reach CSF)
______ is used to treat severe mycoses in pregnant patients
amphotericin B
(1) is the nearly universal side-effect from amphotericin B where (2) and (3) measures can be taken to minimize (1)
1- Infusion-related toxicity: fever/chills, muscle spasms, vomiting, HA, hypotension
2- slow infusion rate OR dec daily dose
3- pretreat with antihistamines, glucocorticoids, antipyretics, or analgesics
Besides infusion related toxicity, (1) is the main mechanism of the other common side effect of amphotericin B. (2) are the three major signs of toxicity from (1) and (3) can be given to slow (1) process. (4) is the other major result of toxicity from (1).
1- amphotericin B binds cholesterol –> forming pores –> renal toxicity
2- azotemia (high N in blood), slight dec GFR, renal tubular acidosis = severe K+/Mg++ wasting
3- Na loading (saline infusion with amphotericin B)
4- hypochromic normocytic anemia via dec EPO
Amphotericin B:
-(1) should be monitored closely during therapy (include all)
-(2) is a direct toxicity from intrathecal administration
1- renal function, LFTs, serum electrolytes (K, Mg), CBC, Hb
2- seizures or other serious neurological damage
Describe the improved formulation of amphotericin B and its advantages
Lipid formulations – adds lipid carrier:
- L-AMB, liposomal amphotericin B
- ABLC, amphotericin B lipid complex
- ABCD, amphotericin B colloidal dispersion
- improves distribution across BBB
- improves efficacy as fungi activate medication via lipases
- decreases AEs: less severe nephrotoxicity
(1) is the main anti-metabolite for treating systemic mycoses, it is a synthetic (purine/pyrimidine).
1- flucytosine
2- pyrimidine
Flucytosine in taken into fungal cells via (1). Then it is first converted into (2) in order to block (3). It is also converted in (4) in order to inhibit (5).
1- cytosine permease
2/3- 5-FU –> 5-FdUMP –> inhibits Thymidylate synthetase –> blocks dTMP synthesis
4/5- 5-FUTP –> inhibits protein synthesis
Flucytosine:
- fungi-(static/cidal)
- (narrow/broad) spetrum
- works best when used with (3), specifically for (4) disease
- used in combination because (5)
1- fungistatic 2- narrow spectrum 3- amphotericin B 4- systemic candidiasis or cryptococcosis 5- to avoid resistance
list the AEs for Flucytosine
- -> metabolized into 5-FU => bone marrow toxicity:
- pancytopenia: anemia, leukopenia, thrombocytopenia
list all the azoles
Imidazoles: *ketoconazole, miconazole, clotrimazole
Triazoles: itraconazole, flucanazole, vorionazole, posaconizole
describe the MOA of Azoles
- inhibition of cytochrome P450 enzyme 14-α-sterol demethylase leading to inhibition of lanosterol —> ergosterol
- reduction in overall ergosterol synthesis
- membrane function is disrupted and permeability is increased => cell death
describe the AEs of Azoles in general
- relatively non-toxic
- minor GI upset is most common AE
describe the additional effects Ketoconazole has in addition to its main MOA (hint- 3)
1) dec plasma testosterone:
- Men: gynecomastia, dec libido, dec potency
- Women: menstrual irregularities
2) high doses inhibits adrenal steroid synthesis and dec plasma cortisol (addison’s)
3) strong CYP3A4 inhibitor –> inc toxicity of drugs (warfarin, cyclosporin)
Ketoconazole:
- (1) describe absorption and distribution
- (2) is the main clinical use
1:
- best absorbed at low gastric pH –> therefore use of antacids, H2 blockers, PPIs => dec absorption
- poor CSF penetration
2: topically for superficial mycoses due to narrow spectrum and high toxicity
