Pharmacology of Antifungal Agents

Fungi are free-living, eukaryotic (nucleated) organisms that exist as yeasts (round fungi), molds (filamentous fungi), or a combination of these two (dimorphic fungi). Although there are more than 100,000 fungal species, only a few are intrinsically pathogenic in humans (Table 1).4 Most pathogenic fungi are saprophytic members of the soil microbial flora, i.e., they live on decaying organic matter. For these organisms, the respiratory system is the most common portals of entry.

Table 1. Selected primary and opportunistic human mycoses.4
Organisms Clinical Manifestations
Primary fungal infections
Blastomycis dermatitidis Pulmonary blastomycosis
     • Hematogenous dissemination
Coccidioides inimitis Pulmonary coccidioidomycosis
     • Hematogenous dissemination
Histoplasma capsulatum Pulmonary histoplasmosis
     • Hematogenous dissemination
Paracoccidioides brasiliensis Paracoccidioidomycosis of the lungs, skin, mucous membrane, and lymph nodes
     • Hematogenous and lymphatic dissemination
Opportunistic fungal infections
Aspergillus sp. Aspergillosis of the lungs, sinuses, and ear canals
     • Hematogenous dissemination
Candida sp.
     • C. albicans
     • C. dublinensis
     • C. glabrata
     • C. krusei
     • C. parapsilosis
     • C. tropicalis
Mucocutaneous candidiasis
     • Hematogenous dissemination
Mucor sp. Mucormycosis of the nose and palate
     • Hematogenous dissemination
Sporothix sp. Lymphocutaneous sporotrichosis
     • Hematogenous dissemination

Some of the other fungi, such as the Candida species, are opportunistic members of the normal human flora (Table 1).4 These organisms are found typically on oral, vaginal, and gastrointestinal mucosa; or as residents on skin, and at times, on respiratory epithelium. Acquired or therapeutic immunosuppression (e.g., HIV infection, corticosteroids, and antimetabolites), diabetes mellitus, lymphoma, leukemia, and tuberculosis predispose patients to oropharyngeal and systemic candidal infections.