Clinical safety rating: caution
Human studies have proved safety
Fluconazole is a triazole antifungal agent that inhibits fungal cytochrome P450 14α-demethylase, thereby blocking the conversion of lanosterol to ergosterol, an essential component of the fungal cell membrane.
| Metabolism | Fluconazole is minimally metabolized, with approximately 11% of the dose excreted unchanged in urine. Metabolites are inactive. The primary metabolic pathway involves N-oxidation and glucuronidation, but specific enzymes have not been fully characterized. |
| Excretion | Renal: approximately 80% as unchanged drug; biliary/fecal: ~11% as metabolites and unchanged drug. |
| Half-life | Terminal elimination half-life ~30 hours (range 20-50 h) in patients with normal renal function; prolonged in renal impairment (up to 98 h in CrCl <20 mL/min). This long half-life supports once-daily dosing and allows loading dose administration. |
| Protein binding | Low to moderate: ~11-12% bound to albumin. Binding is independent of concentration. |
| Volume of Distribution | Vd ~0.7 L/kg (range 0.6-0.8 L/kg). Indicates extensive distribution into total body water and tissues; achieves high concentrations in CSF, ocular fluids, urine, skin, and vaginal tissue. |
| Bioavailability | Oral: >90% (virtually complete). IV: 100% (by definition). |
| Onset of Action | Oral: therapeutic effect typically begins within 24-48 hours; IV: clinical response can be observed within 24 hours. For vaginal candidiasis, single oral dose shows symptom relief within 24-48 hours. |
| Duration of Action | Duration of action: ~24-36 hours based on half-life; clinical effect persists for days after discontinuation due to slow elimination. Single-dose oral therapy for vaginal candidiasis provides efficacy for 3-5 days. |
| Molecular Weight | 306.27 |
200-400 mg orally or intravenously once daily. For candidemia and other invasive Candida infections, loading dose of 800 mg (12 mg/kg) on day 1, then 400 mg (6 mg/kg) daily.
| Renal impairment | Creatinine clearance >50 mL/min: no adjustment; 10-50 mL/min: 50% of recommended dose; <10 mL/min (not on dialysis): 50% of recommended dose given every 48 hours. Hemodialysis: administer after each dialysis session. Continuous renal replacement therapy: 400-800 mg every 24 hours. |
| Liver impairment | Child-Pugh class A: no adjustment; Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: reduce dose by 75% or consider alternative therapy. Monitor liver function tests closely. |
| Pediatric use | Loading dose: 12 mg/kg (max 800 mg) on day 1, then 6 mg/kg (max 400 mg) once daily for invasive candidiasis. For mucosal candidiasis: 3-6 mg/kg once daily (max 200 mg). For neonates: 12 mg/kg every 72 hours (first week of life) then every 48 hours (2-4 weeks). |
| Geriatric use | No specific dose adjustment based solely on age. Adjust dose based on renal function (see renal adjustment). Monitor for QT prolongation and drug interactions due to polypharmacy. |
| 1st trimester | Avoid unless essential; associated with increased risk of spontaneous abortion and congenital anomalies (e.g., craniofacial, skeletal) at high doses (400-800 mg/day). |
| 2nd trimester | Use only if benefit outweighs risk; continuous high-dose therapy may increase risk of preterm delivery. |
| 3rd trimester | Use with caution; high doses near term may cause neonatal fluconazole accumulation. |
Clinical note
Oral fluconazole has a significant gestational-age-dependent risk profile. A single low dose (150 mg) for vaginal candidiasis is commonly used but increasingly scrutinized: a large 2016 Danish cohort (n=3,315) found a doubling of spontaneous abortion risk, and a 2020 NEJM study identified a significant association between single-dose and high-dose fluconazole use in T1 and cardiac septal defects. High-dose prolonged fluconazole (400–800 mg/day) is a known teratogen causing a distinctive skeletal malformation syndrome. Use topical azoles (clotrimazole, miconazole) as first-line for vaginal candidiasis.
| Placental transfer | Fluconazole crosses the placenta extensively; cord blood concentrations are similar to maternal plasma concentrations. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to fluconazole or any azole antifungalsConcomitant use with terfenadine (if fluconazole dose >400 mg/day)Concomitant use with cisaprideConcomitant use with pimozideConcomitant use with quinidineConcomitant use with erythromycin (potential for QT prolongation)
| Precautions | Hepatotoxicity: Monitor liver function; discontinue if signs of hepatic injury occur., QT prolongation: Risk increases with higher doses; caution in patients with electrolyte abnormalities or concurrent QT-prolonging drugs., Adrenal insufficiency: Rare, particularly with prolonged use., Renal impairment: Dose adjustment required for creatinine clearance <50 mL/min., Teratogenic effects in animal studies; use during pregnancy only if clearly needed. |
| Food/Dietary | No significant food interactions. Grapefruit juice may increase fluconazole exposure moderately, but no strict avoidance needed. Avoid alcohol due to hepatotoxicity risk. |
Loading safety data…
| Breastfeeding | Fluconazole is excreted into human milk in concentrations similar to plasma. Doses up to 200 mg/day are considered compatible with breastfeeding; monitor infant for potential adverse effects like diarrhea or hepatic enzyme elevation. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Fluconazole is associated with a dose-dependent risk of teratogenicity. First trimester exposure to high doses (≥400 mg/day) has been linked to a rare but specific pattern of malformations including craniosynostosis, humeral-radial fusion, and congenital heart defects. Low-dose exposure (150 mg single dose) shows minimal increased risk. Second and third trimester exposure: no clear association with major malformations, but prolonged high doses may increase risk of spontaneous abortion or preterm delivery. |
| Fetal Monitoring | Monitor maternal liver function tests (LFTs) and renal function regularly. In prolonged therapy, monitor for signs of hepatic toxicity. Fetal monitoring: ultrasound for growth and anatomy if high-dose exposure in first trimester. Observe neonate for signs of adrenal insufficiency if maternal treatment continued until delivery. |
| Fertility Effects | Fluconazole does not impair fertility in animal studies. Human data on direct effects on fertility are lacking. It may inhibit estrogen synthesis in vitro, but clinical relevance is uncertain. No significant impact on spermatogenesis or ovulation reported. |
| Clinical Pearls | Fluconazole has excellent oral bioavailability (over 90%) with no significant food effect. Adjust dose in renal impairment (CrCl <50 mL/min: reduce dose by 50%). Monitor liver function tests due to risk of hepatotoxicity. Inhibits CYP2C9, CYP2C19, and CYP3A4, increasing levels of warfarin, phenytoin, and oral hypoglycemics. Not effective against Candida krusei or Aspergillus. Consider therapeutic drug monitoring for serious infections (target trough 5-10 mcg/mL). |
| Patient Advice | Take exactly as prescribed; do not skip doses even if you feel better. · You can take with or without food; if you have stomach upset, take with food. · Complete the full course, even if symptoms improve, to prevent resistance. · Report any signs of liver problems: yellowing skin/eyes, dark urine, severe nausea/vomiting, unusual tiredness. · Inform your doctor if you are pregnant or breastfeeding. · Use effective contraception during treatment and for at least 1 week after last dose if you are a woman of childbearing potential. · Avoid alcohol due to potential liver strain. · Notify your doctor if you have kidney disease, as dose adjustments may be needed. · Do not take antacids before or after this without your doctor's approval. · Report any signs of allergy: rash, itching, swelling, difficulty breathing. |