Formulary
Fluconazole: Uses, Dosing, Side Effects and Indian Brand Names
Fluconazole is the most used oral azole antifungal with excellent CNS penetration, first-line for cryptococcal meningitis maintenance and candidiasis, but inactive against moulds and intrinsically resistant Candida krusei.
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Fluconazole: Uses, Dosing, Side Effects and Indian Brand Names
Fluconazole is the most used oral azole antifungal with excellent CNS penetration, first-line for cryptococcal meningitis maintenance and candidiasis, but inactive against moulds and intrinsically resistant Candida krusei.
NEET PG High-Yield: Inhibits lanosterol 14-alpha-demethylase (CYP51). Excellent oral bioavailability (>90%) and CNS penetration (50-80% of serum in CSF). Candida krusei is INTRINSICALLY resistant. C. glabrata has dose-dependent susceptibility. Does NOT cover moulds (Aspergillus, Mucor). CYP2C9 inhibitor (warfarin interaction). Renal excretion (dose adjust in CKD). Single 150 mg dose for VVC. Cryptococcal maintenance therapy. Category D at high doses in pregnancy.
Clinical overview
Fluconazole is the most widely used azole antifungal, valued for its excellent oral bioavailability (>90%, unaffected by food or gastric pH), good CNS penetration (achieving 50-80% of serum levels in CSF), and a relatively favourable safety profile compared to amphotericin B. It is the drug of choice for cryptococcal meningitis (induction with amphotericin B + flucytosine, then consolidation and maintenance with fluconazole), oropharyngeal and oesophageal candidiasis (particularly in HIV/AIDS), and uncomplicated vulvovaginal candidiasis (single 150 mg oral dose). Fluconazole has excellent activity against Candida albicans, Candida parapsilosis, and Cryptococcus neoformans, but has intrinsic resistance from Candida krusei and dose-dependent susceptibility in Candida glabrata -- this spectrum distinction is commonly tested. It does NOT cover moulds (Aspergillus, Mucor) -- voriconazole or amphotericin B are needed for invasive aspergillosis, and amphotericin B for mucormycosis. Fluconazole is a significant CYP2C9 and CYP3A4 inhibitor, creating important drug interactions with warfarin, phenytoin, cyclosporine, and statins. The drug is primarily renally excreted and requires dose adjustment in renal impairment. In India, fluconazole is critical for managing the growing burden of opportunistic fungal infections in HIV patients, transplant recipients, and ICU patients, and is available through NACO for HIV-associated fungal infections.
Pharmacological class
Fluconazole belongs to the Azole Antifungals (Triazole) class. Inhibits fungal lanosterol 14-alpha-demethylase (CYP51), a cytochrome P450 enzyme that converts lanosterol to ergosterol. Ergosterol is the principal sterol in the fungal cell membrane (equivalent to cholesterol in mammalian cells). Depletion of ergosterol increases membrane permeability, disrupting fungal cell growth. Fluconazole is fungistatic against most Candida species and some moulds.
Indian brand names and formulations
Available as: Zocon (FDC), Forcan (Cipla), Flucos (Mankind), Diflucan (Pfizer).
Tablets/Capsules: 50 mg, 100 mg, 150 mg, 200 mg, 400 mg. Oral suspension: 50 mg/5 mL, 200 mg/5 mL. IV infusion: 200 mg/100 mL in normal saline.
Regulatory status
Fluconazole is classified under Schedule H in India under the Drugs and Cosmetics Act, 1940. Prescription-only. Available through NACO for HIV patients. OTC sale of single 150 mg dose for vulvovaginal candidiasis is common but technically requires a prescription.
Indications
- Oropharyngeal candidiasis (first-line)
- Oesophageal candidiasis
- Vulvovaginal candidiasis (single 150 mg dose for uncomplicated cases)
- Cryptococcal meningitis (consolidation and maintenance therapy after induction with amphotericin B + flucytosine)
- Candidaemia and invasive candidiasis (susceptible species)
- Candida urinary tract infections
- Prophylaxis in immunocompromised patients (bone marrow transplant, prolonged neutropenia)
Dosing
Oropharyngeal candidiasis: 200 mg on day 1, then 100-200 mg daily for 7-14 days. Oesophageal candidiasis: 200-400 mg daily for 14-21 days. VVC: 150 mg single oral dose. Cryptococcal meningitis: consolidation 400 mg daily for 8 weeks, then maintenance 200 mg daily. Candidaemia: loading 800 mg, then 400 mg daily. Renal impairment: reduce dose by 50% if CrCl <50 mL/min.
Contraindications
- Known hypersensitivity to azole antifungals
- Co-administration with terfenadine or cisapride (QT prolongation risk)
- Co-administration with high-dose, short-acting simvastatin or lovastatin (rhabdomyolysis risk)
Adverse effects
- GI disturbances (nausea, vomiting, abdominal pain, diarrhoea)
- Headache
- Hepatotoxicity (elevated transaminases; rarely fulminant hepatic failure; monitor LFTs in prolonged use)
- QT prolongation (dose-dependent; caution with other QT-prolonging drugs)
- Rash (discontinue if progressive)
- Alopecia (with prolonged high-dose use)
Drug interactions
- Warfarin: fluconazole inhibits CYP2C9, significantly increasing INR (one of the most important interactions; reduce warfarin dose and monitor INR closely)
- Phenytoin: increased levels via CYP2C9 inhibition
- Cyclosporine and tacrolimus: increased levels via CYP3A4 inhibition; monitor trough levels
- Statins (simvastatin, atorvastatin): increased levels and myopathy risk
- Rifampicin: induces fluconazole metabolism, may reduce efficacy; increase fluconazole dose
- Oral hypoglycaemics (glipizide, glibenclamide): increased levels and hypoglycaemia risk
Pregnancy and lactation
Category D for high-dose/prolonged use (associated with congenital anomalies resembling Antley-Bixler syndrome at doses >400 mg/day). Category C for single low-dose (150 mg) for VVC. Avoid in pregnancy unless the benefit clearly outweighs the risk. Topical azoles (clotrimazole) preferred for VVC in pregnancy.
Exam-style clinical scenario
An HIV patient with CD4 30 cells/microL presents with headache, fever, and neck stiffness. India ink preparation of CSF shows encapsulated budding yeast. After 2 weeks of induction with amphotericin B + flucytosine, what is the next step? Consolidation with fluconazole 400 mg daily for 8 weeks, then maintenance with fluconazole 200 mg daily until immune reconstitution (CD4 >200 for >6 months).
Cost in India
Rs 10-30 per 150 mg tablet. Oral suspension: Rs 60-100 for 35 mL. IV: Rs 50-150 per 200 mg/100 mL infusion.
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
Why is Candida krusei intrinsically resistant to fluconazole?
C. krusei has an altered CYP51 (lanosterol demethylase) enzyme with reduced binding affinity for fluconazole. This is an intrinsic (primary) resistance, not acquired -- all C. krusei isolates are resistant regardless of prior drug exposure. If C. krusei is identified, switch to voriconazole, an echinocandin (caspofungin, micafungin), or amphotericin B.
How does fluconazole differ from itraconazole and voriconazole?
Fluconazole: best CNS penetration, excellent oral bioavailability, no mould coverage, renal excretion. Itraconazole: broader spectrum (covers Aspergillus, Histoplasma, Blastomyces), poor CNS penetration, erratic absorption (requires acidic pH), hepatic metabolism. Voriconazole: covers Aspergillus (drug of choice for invasive aspergillosis), good CNS penetration, visual disturbances as a unique side effect, CYP2C19 metabolism (genetic polymorphism).
Why is fluconazole preferred for cryptococcal maintenance?
Fluconazole has the best oral bioavailability of any azole (>90%), excellent CNS penetration (50-80% of serum levels in CSF -- essential for a meningeal infection), once-daily dosing, and a well-established safety profile for long-term use. It is also affordable and widely available in India through NACO programmes. No other antifungal matches this combination for prolonged outpatient oral maintenance of a CNS infection.
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