2. Types of fungal infections - Mycoses
• Superficial mycoses
– Affect the skin, hair and nails
• Subcutaneous mycoses (tropical)
– Affect the muscle and connective tissue immediately below
the skin
• Systemic (invasive) mycoses
– Involve the internal organs
– Primary vs. opportunistic
• Allergic mycoses
– Affect lungs or sinuses
– Patients may have chronic asthma, cystic fibrosis or sinusitis
There is some overlap between these groups
3. What are the targets for antifungal therapy?
Cell membrane
Fungi use principally ergosterol
instead of cholesterol
Cell Wall
Unlike mammalian cells, fungi have a
cell wall
DNA Synthesis
Some compounds may be selectively
activated by fungi, arresting DNA
synthesis.
6. Azoles - Mechanism
In fungi, the cytochrome P450-
enzyme lanosterol 14-a
demethylase is responsible for the
conversion of lanosterol to
ergosterol
Azoles bind to lanosterol 14a-
demethylase inhibiting the
production of ergosterol
Some cross-reactivity is seen with
mammalian cytochrome p450
enzymes
Drug Interactions
Impairment of steroidneogenesis
(ketoconazole, itraconazole)
8. Azoles - Pharmacodynamics
• Concentration-independent fungistatic
agents
– Dosage escalation may be necessary when
faced with more resistant fungal species (e.g.
Candida glabrata)
• Goal of dosing is to maintain AUC:MIC >50
– i.e. maintain concentrations 1-2 x MIC for the
entire dosing interval
9. Ketoconazole
• Spectrum: yeasts and moulds - poor absorption
limits its role for severe infections, generally used
in mucosal infections only
• Pharmacokinetics
– Variable oral absorption, dependent on pH (often given
with cola or fruit juice)
– T1/2 7-10 hours
– Protein binding > 99%
– Hepatic, bile and kidney elimination
10. Ketoconazole - Adverse effects
• Adverse effects
– N&V, worse with higher doses (800 mg/day)
– Hepatoxicity (2-8%), increase in transaminases,
hepatitis
– Dose related inhibition of CYP P450 responsible for
testosterone synthesis
• Gynecomastia, oligosperma, decreased libido
– Dose-related inhibition of CYP P450 responsible for
adrenal cortisol synthesis
11. Ketoconazole - Drug Interactions
• Potent inhibitor of cytochrome P450 3A4
– Rifampin and phenytoin decrease ketoconazole levels
– Ketoconazole increases cyclosporin, warfarin,
astemizole, corticosteroid, and theophylline levels
– Many of these drug interactions are severe
• Drugs that increase gastric pH will decrease blood
levels of ketoconazole
– Antacids, omeprazole, H2 blockers
15. Fluconazole - spectrum
• Good activity against C. albicans and
Cryptococcus neoformans
• Non-albicans Candida species more likely to
exhibit primary resistance
C. krusei > C. glabrata > C. parapsilosis
C. tropicalis
C. kefyr
Always resistant Sometimes resistant
16. Fluconazole - resistance
• Primary resistance (seen in severely ill or
immunocompromised patients)
– Selection of resistant species or subpopulations
– Replacement with more resistant strain
• Secondary resistance (seen in patients with
AIDS who experienced recurrent
orophayrngeal candidiasis and received long-
term fluconazole therapy)
– Genetic mutation
– Upregulation of efflux pumps
17. Mechanisms of antifungal resistance
• Target enzyme
modification
• Ergosterol biosynthetic
pathway
• Efflux pumps
• Drug import
18. Fluconazole - What is not covered
• Candida krusei
• +/- Candida glabrata
• Aspergillus species and other moulds
19. Fluconazole - Pharmacokinetics
• Available as both IV and PO
– Bioavailibility > 90%
• Linear pharmacokinetics
– t 1/2 = ~24 hours
– Cmax (400 mg IV) = 20 µg/ml (steady state)
– Protein binding < 12%
– Vd 0.85 L/kg (widely distributed)
– >90% excreted unchanged through the kidney
20. Fluconazole - adverse effects/monitoring
• N&V, rash:
– More likely with high doses and in AIDS patients
– Asymptomatic increase in LFTs (7%)
• Drug interactions:
– May increase phenytoin, cyclosporin, rifabutin,
warfarin, and zidovudine concentrations
– Rifampin reduced fluconazole levels to half
(even though FLU is not a major substrate)
21. Fluconazole - Dosing
• Mucosal candidiasis
– 100-200 mg/day (150 mg tablet vulvovaginal candidiasis)
• Systemic fungal infections
– 400-800 mg q24h
– > 800 mg q24h in unstable patient, S-DD isolate, or if non-
albicans spp. (except C. krusei)
• Maintenance for cryptococcal meningitis
– 400 mg q24h
22. Key Biopharmaceutical Characteristics of
the Triazole Antifungals
Fluconazole Itraconazole Voriconazole
Spectrum vs.
Candida and
Aspergillus
C. albicans, C.
tropicalis +/-
C. glabrata
No Aspergillus
Similar Candida
coverage as
fluconazole, +
Aspergillus
Broad, includes
most Candida spp.,
Aspergillus,
Fusarium sp. Not
Zygomycoses
Oral formulation
(% bioavailibility)
Tablet (>90%) Capsule (6-25%)
Solution (20-60%)
Tablet (>90%)
Intravenous
formulation
Available, no
solubilizer
Available, cyclodextrin Available,
cyclodextrin
Clearance Renal (80%) Hepatic 3A4 Hepatic 2C19, 3A4
Serum half life (hr) 24 24-30 6-24
CSF penetration Excellent Poor Excellent
CYP 3A4 inhibition Weak Strong Moderate-Strong
Adverse effects N&V, hepatic N&V, diarrhea
(solution), hepatic, CHF
N&V, visual
disturbances,
hepatic, rash
23. Itraconazole Solution - Side Effects
• Taste disturbances
• Nausea and vomiting
• Osmotic diarrhea (especially at doses > 400
mg/day)
– Long-term compliance often difficult
24. Voriconazole - Side Effects
• Visual disturbances (~ 30%)
– Decreased vision, photophobia, altered color perception
and ocular discomfort
– IV > oral
– No evidence of structural damage to retina
• Reversible alterations in function of retinal rods and cones
• Testing 2 weeks after the end of treatment demonstrates a
return to normal function
• Long term effects?..caution against night-time driving
– Effects may be intensified by hallucinations (2-5%)
25. Amphotericin B
• Polyene antibiotic
• Fermentation product of Streptomyces
nodusus
• Binds sterols in fungal cell membrane
• Creates transmembrane channel and
electrolyte leakage.
• Active against most fungi except Aspergillus
terreus, Scedosporium spp.
27. Amphotericin B
• Classic amphotericin B deoxycholate
(Fungizone™) formulation: serious toxic
side effects.
• Less toxic preparations:
1) Liposomal amphotericin B
2) Amphotericin B colloidal dispersion
3) Amphotericin B lipid complex
28. Amphotericin B - Pharmacokinetics
• Absorption from the GI tract is negligible
– Oral solution sometimes used to decontaminate gut;
few side effects
• Only reliable method of administration is IV
• Selective distribution into deep tissue sites, with
slow release of drug
kidney > liver > spleen > lung > heart > skeletal muscle > brain > bone > CSF > eye
LowHigh
29. Amphotericin B - Metabolic elimination
• Metabolic fate is unknown, drug accumulates in
tissues and then is slowly released
– Drug levels can be measured in the kidney, liver, and
spleen up to 1 year after receiving drug
• Dosages of amphotericin B are generally not
altered due to decreased elimination of the drug
in kidney dysfunction
• Hemodialysis does not alter serum drug
concentrations except in hyperlipidemic patients
30. Amphotericin B - Elimination
• Inverse correlation between patient age and
elimination of AmB,
– Age, elimination, side effects
• Paediatric patients often tolerate
amphotericin B better than adults
31. Amphotericin B - Nephrotoxicity
• Most significant delayed toxicity
• Renovascular and tubular mechanisms
– Vascular-decrease in renal blood flow leading to drop
in GFR, azotemia
– Tubular-distal tubular ischemia, wasting of potassium,
sodium, and magnesium
• Enhanced in patients who are volume depleted or
who are on concomitant nephrotoxic agents
32. Amphotericin B - Manoeuvers employed to
blunt nephrotoxicity…
• Sodium loading-> blunt the
vasoconstriction and tubular-glomerular
feedback
– Administration of 500 ml -1000 ml of NaCl
before and after amphotericin B infusion
34. Amphotericin B - Clinical Uses
The drug of choice for:
• Cryptococcal meningitis
• Mucormycosis (zygomycosis)
• Invasive fungal infection, not responding to
other therapy
35. Amphotericin B - Dosing and Administration
• “Test dose” 1.0 mg in 25-100ml 5% dextrose
infused over 10 minutes used to evaluate
possibility of anaphylactic reaction
– No longer recommended, current product has fewer
impurities
– Current recommendation- Start with ~30% of target
dose, infuse for 15 minutes, stop infusion, and monitor
patient for adverse effects before resuming infusion
– Rapidly escalate to full dosages within 48-72 hours
• Delay in giving full dose = worse clinical outcome
38. Flucytosine
• Restricted spectrum of activity.
• Acquired Resistance.
> result of monotherapy
> rapid onset
Due to:
1) Decreased uptake (permease activity)
2) Altered 5-FC metabolism (cytosine deaminase or
UMP pyrophosphorylase activity)
39. Flucytosine - pharmacokinetics
Oral absorption complete
Plasma half-life 3-6 hrs
Volume of distribution 0.7-1l/kg (low)
Plasma protein binding ~12%
40. Flucytosine - side effects
• Infrequent – include D&V, alterations in liver
function tests and blood disorders.
• Blood concs need monitoring when used in
conjunction with Amphotericin B.
41. Flucytosine – Clinical uses
• Candidiasis
• Cryptococcosis
• ?Aspergillosis
}
In combination with
amphotericin B or
fluconazole.
Monotherapy : now limited
44. Echinocandins - Pharmacology
• Cyclic lipopeptide antibiotics that
interfere with fungal cell wall
synthesis by inhibition of ß-(1,3) D-
glucan synthase
• Loss of cell wall glucan results in
osmotic fragility
Spectrum:
– Candida species including non-
albicans isolates resistant to
fluconazole
– Aspergillus spp. but not activity
against other moulds (Fusarium,
Zygomycosis)
– No coverage of Cryptococcus
neoformansOH
H H
HO
OH
H NH
O
NHH
HO
H2N
HO O
N
H
H3C
HO H
H
O
NH
H
HO OH
H
H NH
NH
O
CH3
OH
H
HO
N
O
H
OH
H
45. Echinocandins - spectrum
Highly active
Candida albicans,
Candida glabrata,
Candida tropicalis,
Candida krusei
Candida kefyr
Pneumocystis carinii
Low MIC ,with
fungicidal activity and
good in-vivo activity.
Very active
Candida parapsilosis
Candida gulliermondii
Aspergillus fumigatus
Aspergillus flavus
Aspergillus terreus
Candida lusitaniae
Low MIC, but without
fungicidal activity in
most instances.
Some activity
Coccidioides immitis
Blastomyces
dermatididis
Scedosporium species
Paecilomyces variotii
Histoplasma
capsulatum
Detectable activity,
which might have
therapeutic potential for
man (in some cases in
combination with other
drugs).
47. Echinocandins-Spectrum vs. Moulds
Staining with antisera
to glucan synthase
subunit (Fks1p)
• Active against Aspergillus
species
– Glucan synthase localized in
apical tips
• Activity against other yeast
and moulds is less well
described or variable
– Mycelial forms of endemic
mycoses?
Aniline blue staining of
β (1-3) glucans –stains
only at apex
48. Caspofungin - Pharmacokinetics
Absorption < 2%
Distribution (Vd) 9.67 L
Protein binding 97% albumin
Major metabolic pathway Peptide hydrolysis, slow
N-acetylation
t 1/2 ß 9-11 hours
CNS penetration
Dosage adjustment
Probably poor
Moderate-severe hepatic dysfunction
Drug-Drug interactions Significant interactions CSA? FK-
506, mycophenolate? Inducers of
3A4?
49. Caspofungin acetate
• IV only
Indication:
– Invasive candidiasis
– Invasive aspergillosis refractory to other therapies
Dosage and administration
– 70 mg day 1, followed by 50 mg daily
• Increase to 70 mg per day in non-responders
• Decrease to 35 mg per day in moderate-severe hepatic
dysfunction (Child-Pugh 7-9)
50. Caspofungin - Adverse effects
• Most common AEs are infusion related:
– Intravenous site irritation (15-20%)
– Mild to moderate infusion-related AE including fever,
headache, flushing, erythema, rash (5-20%)
– Symptoms consistent with histamine release (2%)
• Most AEs were mild and did not require treatment
discontinuation
• Most common laboratory AE
– Asymptomatic elevation of serum transaminases (10-
15%)
• Clinical experience to date suggests that these drugs are
extremely well-tolerated
51. Polyenes
Amphotericin B
deoxycholate
Lipo-AMB (AmBisome)
ABLC (Abelcet)
Amphocil
1 mg/kg/day IV
3 mg/kg/day IV
5 mg/kg/day IV
3 mg/kg/day IV
£7
£554
£246
£380
Triazoles
Fluconazole
Itraconazole
Voriconazole
400/800 mg IV
400 mg IV
4 mg/kg IV
£56/£112
£72
£80
Echinocandins
Caspofungin 50 mg IV x 1 day, £334
Drug Dosage AWP Cost/day for
70kg Patient
