1 - SYSTEMIC ANTIFUNGAL AGENTS Flashcards
The 5 main antifungal systemic agents for superficial dermatologic indications I.e. Onychomycosis and tinea capitis include:
(1) terbinafine (allylamine)
(2) itraconazole (triazole)
(3) fluconazole (triazole)
(4) griseofulvin (spiro-benzo[b]furan)
(5) ketoconazole (imidazole)
True
Systemic Griseofulvin (spiro-benzo[b]furan) and ketoconazole (imidazole) have limited use in the management of onychomycosis and other dermatomycoses
True
Terbinafine is an allylamine
True
Itraconazole and fluconazole are first generation triazoles
True (voriconazole, posaconazole, and ravuconazole are second generation triazoles)
Voriconazole, posaconazole, and ravuconazole are second generation triazoles
True (Voriconazole and posaconazole have been respectively approved for the treatment and prophylaxis of invasive fungal infections, whereas ravuconazole is still under clinical investigation)
Griseofulvin is a spiro-benzo[b]furan isolated from the mold Penicillium griseofulvin Dierckx
True
Even though the use of griseofulvin (spiro-benzo[b]furan) has declined in the treatment of superficial fungal infections, it is still widely used for the treatment of tinea capitis in children
True
Ketoconazole is an imidazole
True
Antifungal agents fall into 3 structural families:
(1) triazoles - itraconazole, fluconazole, Voriconazole, posaconazole, ravuconazole
(2) imidazoles - ketoconazole
(3) allylamines - terbinafine, naftifine (topical formulation only)
True (triazoles and imidazoles are subsets of the broader category of azole antifungals)
Itraconazole (triazole) has a bioavailability of 55% and is extensively metabolised by the liver; in contrast to fluconazole (another triazole) which has a bioavailability of >90% and undergoes little hepatic metabolism where much of the dose is excreted as the unchanged parent drug
True (itraconazole should be used with caution in patients with liver disease)
Terbinafine (allylamine) has a bioavailability of 40% and is extensively metabolised by the liver
True (terbinafine should be used with caution in patients with liver disease)
In patients with liver cirrhosis, terbinafine (allylamine) clearance is reduced by approximately 50% compared to normal volunteers and careful monitoring is required
True (terbinafine is metabolised by the liver)
In patients with liver cirrhosis, the itraconazole (triazole) elimination half-life showed a 2-fold increase and careful monitoring is required
True (itraconazole is metabolised by the liver)
70% of Terbinafine (allylamine) is excreted in the kidneys
True (terbinafine clearance is decreased by about 50% in patients with renal insufficiency)
Itraconazole (triazole) bioavailability is slightly reduced for subjects with renal insufficiency
True (use itraconazole with caution in renal impairment)
With the exception of fluconazole (first generation triazole), other antifungal agents I.e. terbinafine (allylamine), itraconazole, Voriconazole, posaconazole (triazoles); and griseofulvin (spiro-benzo[b]furan) are mainly protein bound and metabolised by the liver
True (only 11-12% of fluconazole is membrane bound and undergoes little first pass hepatic metabolism as it is much less lipophilic but rather more hydrophilic than the other Azoles which accounts for its low protein binding)
With the exception of the second generation triazole posaconazole which is excreted in the faeces, the other antifungal agents I.e. terbinafine (allylamine), Itraconazole, fluconazole, Voriconazole (triazoles); and griseofulvin (spiro-benzo[b]furan) are excreted in the kidneys
True
Terbinafine (allylamine) is delivered to the stratum corneum by passive DEJ diffusion through sebum and through incorporation of drug from migrating basal keratinocytes
True
Terbinafine (allylamine) is not detected in eccrine sweat
True (this is in contrast to itraconazole which becomes detected in sweat within 24 hours and is extensively excreted in sebum unlike the other antifungal agents griseofulvin, ketoconazole and fluconazole)
Itraconazole (triazole) is delivered to the skin as a result of passive diffusion from the plasma to the keratinocytes with strong drug adherence to keratin
True
Itraconazole (triazole) becomes detectable in sweat within 24 hours
True (this is in contrast to terbinafine which is not detectable in sweat)
There is extensive excretion of itraconazole (triazole) into sebum
True (whereas excretion of itraconazole into sweat is minimal; in contrast to griseofulvin, and the imidazole ketoconazole)
Itraconazole (triazole) is eliminated as the stratum corneum renews itself and when the hair and nails grow out
True (may persist in the stratum corneum for 3-4 weeks after discontinuation of therapy)
Fluconazole (triazole) accumulates in the stratum corneum through sweat and by direct diffusion through the dermis and epidermis
True (excretion in the sebum may be more limited) - fluconazole is effective in the treatment of cutaneous fungal infections given as a once weekly dose
Griseofulvin (spiro-benzo[b]furan) is metabolised by the liver and mainly excreted in the kidneys
True
Terbinafine (allylamine) and itraconazole (triazole) diffuses into the nail plate via both the nail matrix and nail bed
True
Fluconazole (triazole) diffuses from the nail bed to the nail plate
True
The faster clearance of systemic antifungal agents from the fingernails than toenails is due to the faster outgrowth of fingernails
True
There is potential for ongoing improvement in onychomycosis well after discontinuation of active systemic antifungal therapy as the drug is still detectable in the nail plate beyond active drug therapy
True
Terbinafine (allylamine) is delivered to the hair shaft via sebum and is therefore more effective against tinea capitis caused by endothrix organisms (Trichophyton tonsurans) than against ectothrix infections (Microsporum canis) as terbinafine accumulates preferentially in the hair shaft
True
Itraconazole (triazole) is delivered to the hair by 2 routes:
(1) via the sebum
(2) incorporation into the hair follicle
True
The systemic antifungals interfere with the enzymes involved in the manufacture of ergosterol, a crucial component of the fungal cell membrane
True (deficiency of ergosterol interferes with membrane function and lead to an arrest in cell growth which may be fungicidal or fungistatic)
Terbinafine and topical naftifine (allylamine) inhibit squalene epoxidase, leading to accumulation of squalene followed by a subsequent deficiency of ergosterol
True
Squalene and lanosterol are 2 of the most important precursors that lead to formation of ergosterol, an essential component of all fungal cell wall membranes
True (antifungal agents inhibit the enzymes involved in converting these 2 precursors to ergosterol)
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
The 2 enzymes squalene epoxidase and 14-alpha demethylase play a role in converting squalene > ergosterol (the essential component of fungal cell membranes)
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
Squalene epoxidase converts squalene to precursors of lanosterol
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
14-alpha demethylase converts lanosterol to 14-alpha demethylase lanosterol
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
Both allylamine (terbinafine and naftifine) and benzylamine (butenafine) antifungal agents inhibit the enzyme squalene epoxidase, leading to accumulation of squalene metabolites which are fungicidal in vitro
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
Both triazole (itraconazole, fluconazole) and imidazole (ketoconazole) antifungal agents inhibit 14-alpha demethylase, leading to increase in lanosterol and reduced ergosterol synthesis, which is fungistatic in vitro
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
Accumulation of squalene metabolites is fungicidal in vitro (effect of allylamine and benzylamine antifungal agents inhibiting squalene epoxidase)
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
Accumulation of lanosterol is fungistatic in vitro (effect of azole antifungal agents inhibiting 14-alpha demethylase)
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
The enzyme 14-alpha demethylase is cytochrome P450 dependant, therefore explaining the role of the triazoles (itraconazole, fluconazole) and imidazoles (ketoconazole) as enzyme inhibitors I.e. these Azoles inhibit 14-alpha demethylase in the phase I metabolism systems
True
Step 1 - squalene epoxidase = squalene > precursors of lanosterol
Step 2 - 14-alpha demethylase = precursors of lanosterol > 14-alpha demethyl lanosterol > ergosterol (essential component of all fungal cell wall membranes)
The fungistatic effects of azole antifungals (due to inhibition of 14-alpha demethylase) may explain the incidence of azole-resistant organisms following prophylaxis or long-term therapy
True
Terbinafine (allylamine) and itraconazole (triazole) are similarly effective against the main Trichophyton species T. rubrum, T. mentagrophytes and T. tonsurans; as well as Microsporum species and Epidermophyton floccosum
True (in contrast to Fluconazole triazole agent)
The triazoles (itraconazole and fluconazole) are more effective than terbinafine (allylamine) against Candida alibi and and C. parapsilosis
True
Terbinafine (allylamine) is FDA approved for the treatment of dermatophyte onychomycosis of the toenails and/or fingernails in adults
True
Granule formulation of Terbinafine (allylamine) is also approved for tinea capitis in patients 4 years and older
True
Itraconazole (triazole) is FDA approved for the treatment of dermatophyte onychomycosis of the toenails and/or fingernails in immunocompetent adults
True
Itraconazole (triazole) is also FDA approved in the treatment of systemic mycoses such as blastomycosis, histoplasmosis and aspergillosis in immunocompromised and immunocompetent patients intolerant or refractory to amphotericin B
True
Fluconazole (triazole) is indicated for the treatment of vaginal, oropharyngeal and oesophageal candidiasis, and cryptococcal meningitis
True
Griseofulvin (spiro-benzo[b]furan) is indicated for the treatment of dermatophyte infections of the skin, scalp and nails and the use of griseofulvin is not justified for the treatment of tinea infections that would be expected to respond satisfactorily to topical antifungals
True
Griseofulvin (spiro-benzo[b]furan) is not effective in the treatment of pityriasis versicolor, bacterial infections, candidiasis, or deep mycotic infections
True
Voriconazole (second generation triazole) is indicated for the treatment of invasive aspergillosis, oesophageal candidiasis, candidaemia in non-neutropenic patients and other disseminated candida infections in patients intolerant of or refectory to other therapy
True (posaconazole is indicated for similar conditions)
Resolution of dermatophyte onychomycosis (Trichophyton species, Microsporum species, Epidermophyton species) typically requires oral therapy
True
Although griseofulvin is approved for tinea infections of the nails, it’s affinity for keratin is low and long term therapy of at least 9-12 months is required
True (treatment efficacy is also low, and the newer azole and allylamine antifungals have largely replaced griseofulvin for Onychomycosis)
Treatment efficacy of griseofulvin for onychomycosis is low due to the low affinity for keratitis, therefore the newer azole and allylamine antifungals have largely replaced griseofulvin for Onychomycosis
True
Terbinafine 250mg daily for 6-12 weeks is recommended for fingernail and toenail onychomycosis
True
The FDA approved regimen for toenail onychomycosis in immunocompetent patients with or without fingernail involvement is continuous itraconazole 200mg daily for 12 weeks
True (when only fingernails are infected, pulse itraconazole 200mg BD for 1 week per month for a total of 2 pulses; although pulse therapy for 3-4 pulses has become a standard for toenail onychomycosis as well)