CHAPTER 63

• Antifungal susceptibility testing


  Designed to provide information that helps the physician select the appropriate antifungal agent to treat a specific infection
• Clinical Laboratory Standards Institute (CLSI)


  • Sets the standards for antifungal susceptibility testing
• Interpretative breakpoints


  For fluconazole, itraconazole, and flucytosine are based on experience in treating patients with mucosal infections, but they also appear to be consistent with information assembled for invasive infections
• Problems that complicate the interpretative guidelines

  • Patient's physical condition (immunologic status)
  • Type of infection and the drug's ability to penetrate a closed space (in the case of an abscess)
  • Dose of the drug and its pharmacokinetics
  • Susceptibility testing method used and serum level of drug administered
• Isolates of the same species may exhibit differences in minimum inhibitory concentrations (MICs) because of previous exposure to antifungal agents or acquisition of a genetic mechanism of resistance
• CLSI methods, or validated equivalent methods, for susceptibility of clinically important fungal isolates should be prepared to send the isolate to a reference laboratory for testing
• Common antifungal agents that are traditionally tested

  • Amphotericin B
  • 5-fluorocytosine
  • Ketoconazole
  • Itraconazole
  • Voriconazole
  • Fluconazole
• Reference method for broth dilution antifungal susceptibility testing for yeast (Document M27–A3)


  Approved standard, covers requirements for use of the broth microdilution method, the standards for susceptibility testing are very specific about inoculum size, test medium, incubation time and temperature, and end point of yeasts that cause invasive fungal infections
• Reference method for broth dilution antifungal susceptibility testing of filamentous fungi (Document M38–A2)


  This standard is a microdilution method for molds that cause invasive and cutaneous infections
• Method for antifungal disk diffusion susceptibility testing of yeasts and molds (M51-A), (Document M44–A2)

  This standard provides methodology for disk diffusion testing for Candida spp., including quality control and interpretation guidelines
• Microdilution methods for fermentative yeast (Documents EDef 7.2) and microdilution for condidia–forming molds (EDef 9.1)


  Have been developed by the European Society of Clinical Microbiology (EUCAST)
• Pneumocystis is worldwide in distribution and most commonly presents as pneumonia in an immunocompromised host
• Mode of transmission for Pneumocystis

  Person-to-person via airborne particles
• Immunocompetent individuals appear to be the reservoir for P. jirovecii, which is transmitted to immunodeficient individuals as a pathogen
• Children ages 2 to 4 years have antibodies to Pneumocystis, suggests acquisition early in life
• Pneumocystis DNA is present in 24 of 72 infants, as determined from nasopharyngeal specimens, and seroconversion occurred in 85% of infants by 20 months of age
• Pneumocystis is defined as the most common opportunistic infection among those with HIV or AIDS in the United States
• Introduction of highly active antiretroviral therapy (HAART) for patients with HIV has reduced the incidence of Pneumocystis disease
• DNA testing demonstrate the detection of P. jirovecii in immunocompetent populations
• Antifungal therapy and prevention

  • Polyene macrolide antifungals
  • Azole antifungal drugs
  • Echinocandins
  • Allylamines
• Polyene macrolide antifungals


  Group of complex organic molecules, most of which contain multiple, conjugated, double-bond, and one- to three-ring structures, includes many of the most commonly used antifungal agents, such as amphotericin B, the colloidal and liposomal preparations of amphotericin B, nystatin, and griseofulvin
• Amphotericin B


  Produced by the actinomycete Streptomyces nodosus, commonly infused intravenously to treat deep-seated fungal infections (invasive aspergillosis) and those caused by Candida spp., Cryptococcus spp., and members of the Mucorales, binds the ergosterol component of the fungal cell membrane and alters the selective permeability of this membrane
• Renal insufficiency


  • Most significant adverse reaction associated with amphotericin B therapy, liposomal amphotericin B compounds reportedly diminish this adverse reaction
• Fungi resistant to amphotericin B

  • Pseudallescheria boydii
  • Scedosporium prolificans
  • Aspergillus terreus
  • Trichosporon spp.
  • Fusarium spp
• Rare cases of resistance to amphotericin B

  • Candida albicans
  • C. glabrata
  • Candida guilliermondii
  • Candida tropicalis
  • Cryptococcus neoformans
  • Candida lusitaniae
• Nystatin


  Antifungal antibiotic produced by Streptomyces noursei, not absorbed in the gastrointestinal tract, principally used locally to treat oral or vulvovaginal candidiasis, toxicity of this drug is prohibitive to parenteral use
• Griseofulvin


  Antifungal antibiotic produced by a species of Penicillium, mechanism of action consists of binding microtubular proteins, which are required for mitosis, oral agent used to treat dermatophytoses, which are not responsive to azole antifungal therapy
• Adverse reactions that limit the usefulness of griseofulvin


  • Headache
  • Gastrointestinal disturbances
  • Photosensitivity
• 5–fluorocytosine (flucytosine)


  Pyrimidine base, which is fluorinated in the fifth position, metabolized to 5-fluorouracil, which is incorporated into fungal ribonucleic acid (RNA) and subsequently inhibits protein synthesis, metabolized into fluorodeoxyuridine monophosphate, a potent inhibitor of deoxyribonucleic acid (DNA) synthesis
• Factors that limited the usefulness of flucytosine

  • Side effects
  • Emergence of resistance among Candida spp. and C. neoformans
• Flucytosine and amphotericin B are synergistic and have been used in combination therapy for treating infections by Candida spp. and Cryptococcus spp.
• Azole antifungal drugs


  Group of antifungal agents consists of the imidazoles and the triazoles, contains six carbon ring structures with conjugated double bonds, chloride residues, and five carbon ring structures that contain at least two nitrogen molecules
• Traditionally used agents in the azole antifungal drugs group

  • Clotrimazole
  • Miconazole
  • Fluconazole
  • Itraconazole
  • Voriconazole
  • Ketoconazole
• Newer triazoles


  • Voriconazole
  • Posaconazole
  • Ravuconazole (most recent)
• Voriconazole


  First of the newer agents released and has been the most thoroughly reviewed
• Azole antifungal agents


  Disrupt the integrity of the fungal cell membrane by interfering with the synthesis of ergosterol
• Clotrimazole and miconazole


  Are available for topical or intravaginal application, useful in mild cases of dermatophytosis, including tinea versicolor, adverse reactions include burning, itching, and skin irritation
• Fluconazole


  A triazole that is exceptionally soluble in water, which allows either oral or intravenous administration, typically has excellent activity against most Candida spp. and Cryptococcus spp., therapeutic levels are easily reached in the central nervous system, short-term treatment can lead to resistance in C. albicans, long-term treatment can lead to resistance in C. neoformans in patients with AIDS, side effects are usually minimal, isolates of C. glabrata may be susceptible, dose–dependent susceptible, or resistant, other notable yeasts or yeast–like fungi resistant include Candida krusei and Rhodotorula spp, has no activity against Aspergillus spp., Fusarium spp., or Mucoraceous molds
• Ketoconazole


  Imidazole that is either taken orally or applied topically, useful in mild cases of paracoccidioidomycosis, alternative to amphotericin B for infections caused by Blastomyces or Histoplasma spp., may be used if prolonged oral therapy for chronic mucocutaneous candidiasis is needed, has been reported to treat P, boydii infections, in vivo is fungistatic, because fungicidal levels are not achievable with therapeutic concentrations, adverse reactions include transient elevations in liver enzymes, nausea, dose-related gynecomastia, decreased libido, and oligospermia (males)
• Itraconazole


  Triazole that has a spectrum of activity that is similar to ketoconazole, shown to be effective in cases of aspergillosis, sporotrichosis, cryptococcosis, and onychomycosis, adverse reactions principally include gastrointestinal disturbances, reported side effects include vestibular disturbances, edema, and skin irritations