Fluconazole

Fluconazole is a systemic triazole antifungal that disrupts fungal membrane formation by blocking lanosterol 14-alpha-demethylase, an enzyme required to produce ergosterol.¹ Ergosterol is functionally important to fungi in much the same way cholesterol is important to animal cell membranes, so its depletion impairs growth and membrane integrity.

The medicine is generally fungistatic rather than rapidly fungicidal, though activity varies with the organism and site of infection. It has high oral bioavailability, reaches concentrations in urine and cerebrospinal fluid, and is eliminated mainly through the kidneys.² These properties allow once-daily treatment for many indications, but renal impairment commonly requires dose adjustment.

Fluconazole is widely used for mucosal candidiasis, including vaginal, oral, and esophageal disease, and for selected bloodstream or deep-tissue infections caused by susceptible Candida.³ It is also an established treatment for cryptococcal meningitis, usually as part of a staged regimen after initial amphotericin-based therapy, and may be used to prevent fungal disease in carefully selected high-risk patients.

It is not equally effective against every yeast or mold. Candida krusei is intrinsically resistant, while Candida glabrata often has reduced susceptibility and may require susceptibility testing or a different antifungal.² Treatment depends on the infection site, species, severity, immune status, local resistance patterns, and kidney function rather than on symptoms alone.

Common adverse effects include nausea, abdominal discomfort, headache, and diarrhea; clinically important reactions include liver injury, severe skin reactions, and QT-interval prolongation.⁴ Liver enzyme abnormalities are usually reversible, but jaundice, marked fatigue, dark urine, or severe rash warrants urgent medical assessment.

Fluconazole inhibits several cytochrome P450 enzymes, especially CYP2C9, CYP2C19, and CYP3A4, so it can raise concentrations of medicines such as warfarin, certain sulfonylureas, phenytoin, and some statins.⁵ Clinicians also consider additive cardiac risk with other QT-prolonging medicines. For uncomplicated vaginal candidiasis, oral fluconazole is generally avoided during pregnancy; the CDC recommends topical azole therapy for seven days instead.⁶

Fluconazole’s pharmacology explains several less obvious clinical choices. Unlike many antifungals, it penetrates the cerebrospinal fluid well, which helped establish its role in cryptococcal meningitis, while its predominantly renal elimination distinguishes it from extensively hepatically cleared azoles.²

Resistance can emerge during prolonged exposure, especially in people with advanced immunosuppression or recurrent infection. Mechanisms include changes in the drug target, increased efflux, and altered sterol pathways; prior azole exposure can therefore influence later treatment selection.³ Fluconazole may also be used in veterinary medicine, but human prescriptions should not be substituted or shared. A negative response does not by itself prove resistance: reinfection, an incorrect diagnosis, mixed infection, or inadequate source control may explain persistent symptoms.

Ergosterol

A sterol in fungal cell membranes that is targeted indirectly by many azole antifungal medicines.

Triazole

A class of antifungal drugs that inhibits fungal sterol synthesis through cytochrome P450-dependent enzymes.

Candidiasis

Infection caused by yeasts of the genus Candida, ranging from localized mucosal disease to invasive bloodstream infection.

Cryptococcal meningitis

A potentially life-threatening infection of the membranes around the brain, usually caused by Cryptococcus neoformans or Cryptococcus gattii.