Fluconazole

Introduction Overview

Generic Name

fluconazole

Brand Name

Diflucan

Dosage Form

oral tablet, oral suspension, injection for intravenous infusion

Drug Class

Azole antifungals

Pharmacokinetics

Absorption:
Fluconazole exhibits excellent oral bioavailability, with rapid and nearly complete absorption from the gastrointestinal tract, achieving plasma concentrations equivalent to intravenous administration. Oral bioavailability approaches 90% or higher, permitting interchangeable oral and IV dosing for most clinical situations. Food intake does not significantly affect absorption, allowing administration with or without meals. The rapid absorption results in peak plasma concentrations within approximately 1-2 hours post administration. This pharmacokinetic profile supports convenient dosing schedules and flexibility in outpatient and inpatient settings.

Distribution:
Fluconazole demonstrates extensive tissue distribution, including penetration into cerebrospinal fluid (CSF), which is critical for treating fungal infections of the central nervous system such as cryptococcal meningitis. The volume of distribution ranges broadly, approximating total body water, reflecting widespread dissemination into body fluids and tissues including skin, sputum, saliva, and urine. It crosses the blood-brain barrier effectively with CSF concentrations reaching 50-90% of plasma levels. Protein binding is low (approximately 11-12%), facilitating free drug availability at sites of infection.

Metabolism:
Unlike many azole antifungals, fluconazole undergoes minimal hepatic metabolism, which reduces the potential for hepatic drug interactions and variable metabolism-related pharmacokinetics. Approximately 80% of an administered dose is excreted unchanged in the urine, highlighting renal clearance as a primary elimination pathway. Minor metabolites are formed but do not significantly contribute to antifungal activity or toxicity. This metabolic stability contributes to its predictable pharmacokinetic profile and allows dosing adjustments primarily based on renal function.

Elimination:
Fluconazole is primarily eliminated by renal excretion of unchanged drug via glomerular filtration and active tubular secretion. The elimination half-life in healthy adults ranges from 30 to 50 hours, supporting once-daily dosing regimens. In patients with renal impairment, the half-life can be prolonged considerably, necessitating dosage adjustments in cases of significant renal dysfunction. Dose reduction is recommended in patients with creatinine clearance less than 50 mL/min for multiple dosing regimens. The predictable elimination and renal excretion pattern contribute to fluconazole's favorable safety and efficacy profile.

Dosage Forms

Available Dosage Forms:
-Fluconazole oral tablets: 50 mg, 100 mg, 150 mg, and 200 mg
-Fluconazole oral suspension (liquid): 10 mg/mL
-Fluconazole intravenous injection (for infusion): available as 2 mg/mL solution

Dosages for Adults and Adolescents:
-Dose varies widely by infection type and severity.
-Vaginal candidiasis: typically single 150 mg oral dose.
-Oropharyngeal candidiasis: 200 mg on day 1, followed by 100 mg once daily.
-Esophageal candidiasis: initial 200 mg dose, then 100-400 mg daily.
-Systemic candidiasis: up to 400 mg/day; duration individualized.
-Cryptococcal meningitis: 400 mg initial dose, then 200-400 mg daily.
-Bone marrow transplant prophylaxis: 400 mg once daily.

Specific Patient Populations:
-Children older than 6 months: dosing based on body weight, typically 6 mg/kg day 1 then 3 mg/kg daily, with dosage escalated for severe infections.
-Children on extracorporeal membrane oxygenation (ECMO): loading dose 35 mg/kg first day, followed by 9 to 12 mg/kg daily depending on gestational age.
-Renal impairment: dosage adjustments recommended when creatinine clearance is below 50 mL/min for repeat dosing.

Clinical guidelines emphasize using oral dosing when feasible due to equivalent bioavailability compared to IV, with IV formulations reserved for patients unable to tolerate or absorb oral therapy or critically ill patients.

Mechanism Of Action

Fluconazole is a triazole antifungal agent that exerts its antifungal effect by selectively inhibiting the enzyme lanosterol 14-alpha-demethylase, a cytochrome P450-dependent enzyme crucial in the biosynthesis of ergosterol. Ergosterol is an essential sterol component of fungal cell membranes, analogous to cholesterol in mammalian cells. By inhibiting lanosterol 14-alpha-demethylase, fluconazole disrupts the conversion of lanosterol to ergosterol, leading to an altered cell membrane composition and increased membrane permeability.

This enzymatic blockade results in the accumulation of 14-alpha-methylated sterols, which are toxic to the fungal cell and disrupt membrane integrity and function. The altered membrane impairs essential processes such as nutrient transport, enzyme activity, and membrane-bound protein function, culminating in fungal cell growth arrest and eventual cell death or fungistatic effects depending on organism susceptibility and drug concentration.

Importantly, fluconazole exhibits a higher affinity for the fungal cytochrome P450 enzyme compared to its human counterpart, minimizing toxicity related to human sterol biosynthesis pathways. This selectivity contributes to the drug’s favorable safety profile relative to other systemic antifungals.

Clinically, this mechanism underpins fluconazole's broad spectrum of activity against many Candida species and Cryptococcus neoformans, with high potency in mucosal and systemic fungal infections. Comparative studies have demonstrated fluconazole’s efficacy and relatively low toxicity compared to other azoles such as ketoconazole or itraconazole, partly due to its unique molecular structure improving selective binding and penetration into infected tissues including the central nervous system. Ongoing research continues to evaluate resistance mechanisms, including mutations in lanosterol 14-alpha-demethylase reducing fluconazole binding, which can diminish therapeutic efficacy in some clinical scenarios.

Pharmacological Actions

Selective inhibition of fungal lanosterol 14-alpha-demethylase enzyme leading to impaired ergosterol synthesis.
Disruption of fungal cell membrane integrity and function resulting in fungistatic or fungicidal effects.
Broad antifungal spectrum including key activity against Candida species and Cryptococcus neoformans.
Excellent penetration into cerebrospinal fluid and other body tissues to treat invasive fungal infections.
Low protein binding facilitating widespread drug distribution in body fluids.
Minimal hepatic metabolism reducing potential for drug-drug interactions via cytochrome P450 enzymes.
Renal excretion as unchanged drug enabling predictable pharmacokinetics and dosing in various patient populations.
Prophylactic antifungal action in immunocompromised patients preventing fungal infections.
Long elimination half-life permitting once-daily dosing schedules.
Activity confirmed in clinical trials against mucosal candidiasis, systemic candidiasis, and cryptococcal meningitis.
Fungal selectivity minimizes adverse effects related to human sterol biosynthesis.
Potential to cause reversible adrenal insufficiency due to impact on steroidogenesis enzymes at higher doses.
Absence of significant effect on bacterial flora, limiting risk of secondary bacterial infections.
Compatibility with oral and intravenous formulations allowing flexible administration.
Relative resistance in certain non-albicans Candida species requiring susceptibility testing.

Therapeutic Or Clinical Uses

Treatment of vaginal candidiasis (vaginal yeast infections).
Management of oropharyngeal and esophageal candidiasis in immunocompetent and immunocompromised patients.
Treatment of Candida urinary tract infections and Candida peritonitis.
Therapy for systemic Candida infections including candidemia, disseminated candidiasis, and Candida pneumonia.
Treatment and prevention of cryptococcal meningitis, especially in HIV/AIDS patients.
Prophylaxis of candidiasis in patients undergoing bone marrow transplantation receiving chemotherapy or radiation.
Prevention of fungal infections in immunocompromised patients such as those with AIDS.
Use in pediatric patients on extracorporeal membrane oxygenation (ECMO) to prevent invasive fungal infections.
Treatment of infections caused by susceptible fungi in patients intolerant to other antifungals.
Empiric antifungal therapy in suspected fungal infections pending culture results.
Secondary prophylaxis to prevent relapse of cryptococcal meningitis in AIDS patients.
Off-label use in certain dermatophytic infections and chronic mucocutaneous candidiasis.
Use in patients with neutropenia to prevent invasive fungal disease.
Treatment adjunct in immunosuppressive therapy to reduce fungal infection risk.
Useful in resource-limited settings due to oral and intravenous formulation availability and cost-effectiveness.

Side Or Adverse Effects

Common side effects including headache, nausea, diarrhea, dizziness, and abdominal pain.
Altered taste perception (dysgeusia) reported in some patients.
Rare but serious allergic reactions including anaphylaxis, angioedema, and skin rash.
Potential hepatotoxicity including elevated liver enzymes and rare cases of serious liver injury or liver failure.
Exfoliative and bullous skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, albeit rarely.
QT interval prolongation leading to risk of cardiac arrhythmias, especially when combined with other QT-prolonging agents.
Reversible adrenal insufficiency reported with prolonged or high-dose therapy.
Thrombocytopenia and leukopenia observed rarely.
Increased liver function tests that often resolve upon discontinuation.
Transient increases in serum creatinine and renal impairment in susceptible individuals.
Possible drug-induced photosensitivity reactions and rash.
Central nervous system effects including dizziness and rare seizures.
Gastrointestinal disturbances such as vomiting and abdominal discomfort.
Potential elevation of bilirubin and other markers indicative of liver stress.
Rare reports of cutaneous lupus erythematosus exacerbation with fluconazole use.

Precautions

Assess for history of allergic reactions to fluconazole or other azole antifungals prior to therapy.
Use with caution in patients with pre-existing liver disease; monitor liver function tests regularly.
Monitor renal function in patients with impaired kidney function and adjust dose accordingly.
Exercise caution when administering to patients with known QT prolongation or electrolyte imbalances, such as hypokalemia.
Avoid use concomitantly with other drugs known to prolong the QT interval or with potential for serious drug interactions.
Pregnant women should use fluconazole only if clearly needed due to potential teratogenic effects; effective contraception recommended for women of childbearing potential.
Lactating women should consult healthcare providers, as fluconazole is excreted in breast milk.
Consider fungal culture and susceptibility testing prior to initiation to tailor antifungal therapy.
Caution in immunocompromised hosts with deep-seated fungal infections due to risk of skin adverse reactions.
Inform patients about signs of liver toxicity and instruct to report symptoms promptly.
Avoid abrupt discontinuation to reduce risk of fungal resistance and relapse.
Evaluate all concurrent medications for potential interactions before initiation.
Patients receiving long-term therapy should be monitored for adrenal insufficiency symptoms.
Careful administration in pediatric populations with dosing adjustments per weight and clinical status.
Oral suspension contains sucrose; caution in patients with sugar intolerance or diabetes.

Warnings

Fluconazole may cause serious hypersensitivity reactions including anaphylaxis; immediate medical attention required if symptoms occur.
Prolonged use associated with rare but severe hepatotoxicity, including fatal cases primarily in patients with underlying health conditions.
Potential to prolong the QT interval, increasing risk of life-threatening cardiac arrhythmias such as torsades de pointes.
Skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported, some fatal; discontinue immediately if rash develops.
May cause fetal harm when administered to pregnant women; contraindicated in pregnancy except for single, low-dose use for vulvovaginal candidiasis.
Reversible adrenal insufficiency may develop with high or prolonged dosing; monitor for symptoms such as fatigue and muscle weakness.
Avoid concomitant use with drugs metabolized by CYP3A4 that also prolong QT interval due to risk of serious interactions.
Use caution in patients with cardiac risk factors, electrolyte disturbances, or concomitant medications affecting heart rhythm.
Risk of drug accumulation and toxicity in renal impairment without dose adjustment.
Concurrent use with certain chemotherapeutic and immunosuppressive agents may require close monitoring due to altered drug levels.
Risk of increased warfarin effect leading to potential bleeding; monitor coagulation parameters closely.
Treatment should be guided by susceptibility data when available to reduce resistance development.
Avoid non-prescribed use to prevent fungal resistance and potential adverse effects.
Should not be used to treat viral infections; no efficacy against viruses.
Do not share medication with others to prevent inappropriate use and adverse outcomes.

Contraindication

Hypersensitivity to fluconazole or any component of the formulation.
Known allergy to azole antifungals such as ketoconazole, itraconazole, voriconazole, or miconazole.
Concurrent administration with drugs known to markedly prolong QT interval and metabolized by CYP3A4 (e.g., cisapride, pimozide, quinidine, astemizole).
Use during pregnancy for indications other than single-dose treatment of vulvovaginal candidiasis due to teratogenic risk.
Patients with previous severe cutaneous adverse reactions to fluconazole or related azoles.
Concurrent use with ergot alkaloids due to risk of ergot toxicity.
Severe hepatic impairment without close monitoring is a relative contraindication.
Use contraindicated in patients with history of congenital long QT syndrome.
Use in neonates and infants younger than specified age without specialist supervision.
Use contraindicated when oral suspension sugar content is incompatible with patient’s medical condition (e.g., hereditary fructose intolerance).
Do not use in patients with untreated serious arrhythmias or electrolyte imbalances increasing arrhythmia risk.
Avoid use in patients taking certain immunomodulators that may lead to enhanced toxicity without monitoring.
Avoid use with certain statins that have severe interaction potential without close monitoring.
Contraindicated in patients with hypersensitivity to injectable formulation components.
Use caution and assess risk-benefit in patients with immune reconstitution inflammatory syndrome (IRIS) secondary to fungal infection treatment.

Drug Interactions

CYP3A4 substrate and inhibitor: fluconazole increases plasma concentrations of drugs metabolized by CYP3A4.
Increased bleeding risk when combined with warfarin; requires close INR monitoring.
Enhances hypoglycemic effects of oral antidiabetics such as glyburide, tolbutamide, and glipizide.
Interacts with calcium channel blockers like amlodipine, nifedipine, felodipine, potentially increasing cardiovascular side effects.
Increases serum levels of cyclosporine, tacrolimus, and sirolimus necessitating dose adjustment and monitoring for toxicity.
Reduces metabolism of phenytoin and carbamazepine leading to increased plasma concentrations and toxicity risk.
Concurrent use with rifampin or rifabutin (potent CYP inducers) decreases fluconazole efficacy.
Potential for enhanced central nervous system toxicity when combined with theophylline.
Erythromycin coadministration increases risk of QT prolongation and cardiac arrhythmias.
May increase plasma concentrations of psychotropic drugs such as amitriptyline, nortriptyline, and pimozide, enhancing side effects.
Interacts with antifungals like voriconazole and amphotericin B requiring careful clinical monitoring.
Increases plasma levels of certain chemotherapeutic agents including vincristine, vinblastine, cyclophosphamide, and olaparib.
Potentiates opioid toxicity with fentanyl, alfentanil, and methadone due to metabolism inhibition.
May require adjustment of statin doses (atorvastatin, simvastatin, fluvastatin) to avoid myopathy and rhabdomyolysis.
Interaction with NSAIDs (celecoxib, ibuprofen, naproxen) can increase risk of adverse renal or gastrointestinal effects.
Prednisone metabolism inhibited, possibly altering steroid efficacy and side effect profile.
HIV antiviral drugs such as saquinavir and zidovudine metabolism may be increased or decreased, requiring monitoring.
Tofacitinib levels may increase due to fluconazole’s CYP inhibition, enhancing immunosuppressive effects.
Vitamin A coadministration could potentiate toxicity requiring clinical vigilance.
Fluconazole significantly prolongs QT interval when combined with other QT-prolonging agents, increasing arrhythmia risk.

Preparations Of The Drug

Fluconazole oral tablets manufactured by ANI Pharmaceuticals, Aurobindo Pharma Limited, and Dr Reddy’s Laboratories Limited.
Fluconazole injection for intravenous infusion made by Baxter Healthcare, Sagent Pharmaceuticals, and Hikma Pharmaceuticals USA Inc.
Fluconazole oral suspension powder prepared by NorthStar Rx LLC, Slate Run Pharmaceuticals, and Aurobindo Pharma Limited.
Brand-name Diflucan tablets and oral suspension produced by Pfizer, distributed by Roerig division of Pfizer Inc.
Generic injectable formulations are available from multiple manufacturers ensuring broad availability.
Oral formulations include sugar-containing suspension necessitating caution in special populations.
Packaging available in various strengths including 50 mg, 100 mg, 150 mg, and 200 mg tablets and 10 mg/mL suspension.
Intravenous formulations supplied as sterile solutions for infusion with stability data allowing room temperature storage.
Product inserts recommend storage at controlled room temperature away from moisture and heat.
Fluconazole suspension should be discarded after 2 weeks of opening to maintain efficacy.
Manufacturers provide patient information leaflets detailing dosing, side effects, and handling instructions.
Quality control standards ensure consistent drug potency, purity, and safety across brands.
Multiple manufacturers enable accessibility of fluconazole globally in both branded and generic forms.
Supplemental materials include dosing syringes with suspension for accurate patient administration.
Injection formulations prepared for infusion with maximum administration rates specified to minimize adverse effects.