Fluconazole

Active Ingredient & Mechanism of Action

• Active Ingredient: Fluconazole.
• Mechanism: Fluconazole is a highly selective inhibitor of the fungal cytochrome P450 enzyme lanosterol 14$\alpha$-demethylase:
  1. Inhibition of Ergosterol Synthesis: By blocking this enzyme, fluconazole prevents the conversion of lanosterol to ergosterol, an essential component of the fungal cell membrane.
  2. Membrane Disruption: The depletion of ergosterol, along with the accumulation of toxic 14$\alpha$-methyl sterols, alters cell membrane permeability and fluidity, inhibiting fungal cell growth and replication (fungistatic effect).

Available Strengths & Dosage Forms

• Oral Tablets: Standard strengths include 50 mg, 100 mg, 150 mg, and 200 mg.
• Oral Suspension: Available as 10 mg/mL and 40 mg/mL liquid formulations (often reconstituted from powder) for pediatric patients or individuals with difficulty swallowing pills.
• Intravenous (IV) Infusion: Ready-to-use solution (2 mg/mL in normal saline or dextrose) for severe or inpatient systemic infections.

Clinical Indications

• Vaginal Candidiasis (Vaginal Yeast Infection): Single-dose oral treatment (150 mg) for acute, uncomplicated infections.
• Oropharyngeal & Esophageal Candidiasis (Thrush): Treatment of mucosal Candida infections in immunocompetent and immunocompromised individuals.
• Systemic Candidiasis: Treatment of candidemia, disseminated candidiasis, and peritonitis.
• Cryptococcal Meningitis: Treatment of active cryptococcal meningitis (often following initial induction therapy with amphotericin B) and long-term suppressive therapy to prevent relapse in patients with HIV/AIDS.
• Antifungal Prophylaxis: Prevention of candidiasis in high-risk patients, such as those undergoing bone marrow transplants, chemotherapy, or advanced immunosuppressive therapy.

Key Pharmacokinetics

• Absorption: Exceptionally well absorbed following oral administration with an absolute bioavailability exceeding 90%. Absorption is not affected by gastric pH or food intake.
• Distribution: Highly water-soluble with low plasma protein binding ($\sim 11\text{–}12\%$). Distributes widely throughout all body tissues and fluids, achieving high concentrations in cerebrospinal fluid (CSF), skin, saliva, and vaginal secretions.
• Elimination & Half-Life: Long elimination half-life of approximately 30 hours in adults, supporting once-daily (or single-dose) administration regimens. Excreted predominantly unchanged through the kidneys into the urine ($\sim 80\%$).

Administration Guidelines

• Usage: Administered orally or via IV infusion once daily (except for single-dose vaginal candidiasis).
• Food Consistency: Can be taken with or without food.
• Renal Adjustment: Because it is cleared primarily by the kidneys, dosage reductions (typically by 50%) are required for patients with moderate to severe renal impairment (creatinine clearance $< 50\text{ mL/min}$).

Safety Profile & Considerations

• Common Side Effects: Headache, nausea, abdominal pain, diarrhea, dizziness, dyspepsia, and mild skin rash.
• Hepatic Safety: Can cause transient elevations in liver enzymes. Rare cases of severe hepatoxicity or hepatic failure have been reported, requiring baseline and periodic liver function monitoring during prolonged therapy.
• Cardiac Risk (QT Prolongation): Can prolong the QT interval on an ECG, carrying a risk of ventricular arrhythmias (including Torsades de Pointes), particularly in patients with structural heart disease, electrolyte imbalances, or those taking other QT-prolonging drugs.
• Pregnancy Warning: High doses or prolonged exposure during the first trimester carry a risk of congenital birth defects. A single 150 mg dose for vaginal thrush should only be used during pregnancy if clearly needed and advised by a physician.
• Key Drug Interactions (CYP450 Inhibition): Fluconazole is a potent inhibitor of CYP2C9 and CYP3C19, and a moderate inhibitor of CYP3A4. It significantly elevates blood levels of many concurrent drugs, including:
  • Warfarin / Coumarin Anticoagulants: Increases prothrombin time and bleeding risk.
  • Oral Hypoglycemics (e.g., Sulfonylureas): Elevates blood levels, increasing the risk of hypoglycemia.
  • Phenytoin & Carbamazepine: Increases anticonvulsant toxicity risk.
  • Statins (e.g., Atorvastatin, Simvastatin): Elevates risk of myopathy and rhabdomyolysis.
  • Calcineurin Inhibitors (e.g., Cyclosporine, Tacrolimus): Increases nephrotoxicity risks.

Note: Fluconazole is a prescription antifungal medication. Treatment duration, dosage adjustments for renal function, and screening for major drug interactions must be managed under direct healthcare supervision.