Fluconazole

Fluconazole is a member of the triazole class of antifungal drugs, part of the wider azole family ^[1]. It is distinguished from earlier azoles such as ketoconazole by carrying two triazole rings in place of an imidazole ring, a change that improved its water solubility and its behaviour in the body; its full chemical name is 2-(2,4-difluorophenyl)-1,3-bis(1H-1,2,4-triazol-1-yl)propan-2-ol, with the formula C13H12F2N6O ^[1]. The drug is well absorbed when swallowed, reaching the bloodstream almost as completely as when injected, is only lightly processed by the liver, and is cleared mostly unchanged by the kidneys; its long half-life allows once-daily dosing ^[1][4].

Fluconazole was discovered by scientists at the pharmaceutical company Pfizer and was patented in the early 1980s ^[1]. It reached the market later that decade under the brand name Diflucan, and after its patents expired in the mid-2000s it became available as an inexpensive generic ^[1]. It is now one of the most widely used antifungal agents and is included on the World Health Organization's List of Essential Medicines ^[1].

The drug is used against yeasts and some other fungi rather than against bacteria ^[1]. Common indications include candidiasis in its various forms, from vaginal and oral thrush to infections of the oesophagus and bloodstream, and it is a mainstay of maintenance therapy for cryptococcal meningitis, a serious infection seen especially in people with weakened immune systems ^[1]. It is also used to prevent fungal infection in patients whose immunity is compromised, for example during chemotherapy or after transplantation, and it has a role in several other systemic mycoses ^[1]. Available as tablets, an oral suspension, and an intravenous solution, it can be matched to the severity of the infection ^[1].

Fluconazole is generally well tolerated, with headache, nausea, abdominal discomfort, rash, and mild rises in liver enzymes among the more frequent complaints; uncommon but serious problems include marked liver injury, severe skin reactions, and a lengthening of the heart's QT interval that can predispose to arrhythmia ^[1][4]. Because it inhibits several drug-metabolising liver enzymes, chiefly CYP2C19 along with CYP3A4 and CYP2C9, it can raise blood levels of many other medications and must be prescribed with attention to interactions ^[1]. Its use in pregnancy is cautioned; a large Danish cohort study linked oral fluconazole taken during pregnancy with a modestly increased risk of miscarriage ^[2]. As with other azoles, fungi can become resistant to fluconazole, commonly through mutations in the target enzyme gene ERG11 or by pumping the drug out of the cell, which is a growing clinical concern ^[3].

Fluconazole is prescription only, though single dose packs are sometimes available for vaginal thrush. Common effects are nausea, headache, abdominal pain, and rash. Less often it can strain the liver, and at higher or prolonged doses it can prolong the QT interval of the heartbeat, which matters in people on other QT prolonging drugs. High doses in pregnancy have been linked to birth defects, so it is used cautiously there. It is a notable enzyme inhibitor, blocking CYP2C9, CYP3A4, and CYP2C19, so it can raise the levels of drugs such as warfarin, phenytoin, certain statins, and some diabetes medicines. Liver checks are wise with long courses.

Fluconazole is a strong CYP2C9 inhibitor and a moderate CYP3A4 and CYP2C19 inhibitor, and the CYP2C9 effect drives the most serious interactions. Warfarin exposure rises and the INR can climb sharply within days, with bleeding reported even after one standard single dose. Phenytoin concentrations rise into the toxic range, and sulfonylureas such as glipizide and glyburide accumulate and cause hypoglycemia.

Through CYP3A4 it raises exposure to tacrolimus, ciclosporin, sirolimus and midazolam, and to the statins cleared by that enzyme.

Fluconazole prolongs the QT interval on its own, so pairing it with amiodarone, sotalol, methadone or ondansetron compounds the torsades risk; co-administration with cisapride and with quinidine is contraindicated for that reason. In the other direction, rifampicin induces fluconazole metabolism and lowers its concentrations enough to risk treatment failure.

Checking a whole stack? Run it through interactions + stacks.

Fluconazole was discovered by scientists at Pfizer, including Kenneth Richardson and colleagues, in the early 1980s during a search for antifungals with better solubility and oral absorption than existing agents. Its distinctive bis-triazole structure, incorporating two fluorine atoms, was designed to make the molecule highly water-soluble and well absorbed when taken by mouth. It was first introduced in 1988 and received Food and Drug Administration approval in 1990 under the brand name Diflucan. The drug arrived at a pivotal moment, becoming a cornerstone therapy for the Candida and cryptococcal infections that afflicted patients during the HIV/AIDS epidemic. Over the following decades it became one of the most widely prescribed antifungals in the world, and it is now available as an inexpensive generic. It appears on the World Health Organization's List of Essential Medicines.

Fluconazole holds an outstanding reputation as one of the most dependable and convenient antifungal medicines ever developed, a true workhorse of infectious disease care. Physicians value its excellent oral absorption, which is so complete that oral and intravenous doses are essentially interchangeable, along with its long duration of action and good penetration into tissues including the cerebrospinal fluid.

This combination makes it a first-line choice for common yeast infections and a critical agent for serious conditions such as cryptococcal meningitis. Its wide availability and low cost as a generic give it enormous global public-health value, reflected in its place on the WHO Essential Medicines List. In fairness, its spectrum is deliberately narrow; molds such as Aspergillus lie beyond its reach, and overuse can drive resistance in Candida, so it is best deployed thoughtfully rather than reflexively.