Fluconazole

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Fluconazole on Prescriptsy

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Fluconazole is a triazole antifungal medicine widely used to treat and prevent infections caused by Candida species and other susceptible fungi.

In the United Kingdom, its most common use is the treatment of vaginal thrush (candidal vulvovaginitis), for which a single 150 mg capsule is available to purchase from a pharmacy without a prescription for women aged 16 to 60 who have previously received a medical diagnosis of thrush.

For other indications, including oral thrush, systemic candidiasis, and cryptococcal meningitis, fluconazole is a prescription-only medicine (POM) available in capsule and oral suspension formulations.

Fungal infections are extremely common in the United Kingdom.

Vaginal thrush affects up to 75% of women at some point in their lives, and around 5 to 8% of women experience recurrent episodes (four or more per year).

Oral thrush (oropharyngeal candidiasis) is particularly common in infants, the elderly, people using inhaled corticosteroids, denture wearers, and immunocompromised individuals.

Systemic candidiasis, while less common, is a life-threatening condition that occurs predominantly in hospitalised patients with central venous catheters, those in intensive care, patients receiving broad-spectrum antibiotics, and immunosuppressed individuals.

This page provides a comprehensive clinical overview of fluconazole, including its mechanism of action, dosing for different infections, side effects, drug interactions, safety warnings, and how to obtain it in the UK.

Important safety information about fluconazole

• A single 150 mg capsule for vaginal thrush can be purchased from pharmacies (P classification) for women aged 16 to 60 with a previous medical diagnosis of thrush.
• Fluconazole interacts with many medicines, including warfarin, statins, and some diabetes drugs. Inform your pharmacist or prescriber of all medications you are taking.
• High-dose fluconazole in the first trimester of pregnancy has been associated with birth defects. Avoid in pregnancy unless the infection is life-threatening.
• Rare but serious side effects include liver damage and severe skin reactions. Seek urgent medical attention if you develop jaundice or widespread skin blistering.
• For vaginal thrush during pregnancy, topical treatments (clotrimazole) are preferred.

Understanding fungal infections treated by fluconazole

Candida species are yeasts that form part of the normal human flora, colonising the gastrointestinal tract, mouth, and vagina without causing harm in most healthy individuals.

When the balance of the microbial environment is disrupted, Candida can overgrow and cause symptomatic infection, termed candidiasis.

Common predisposing factors include antibiotic use (which reduces competing bacterial flora), immunosuppression (HIV, chemotherapy, organ transplantation), diabetes mellitus, pregnancy, use of inhaled or systemic corticosteroids, and iron deficiency.

Vaginal thrush is characterised by vulval itching, soreness, and a thick white "cottage cheese" vaginal discharge.

It is not a sexually transmitted infection, though sexual activity may exacerbate symptoms.

Oral thrush presents as white patches or plaques on the tongue, palate, and buccal mucosa that can be wiped off to reveal a red, raw surface beneath.

It may cause pain, burning, and altered taste. Oesophageal candidiasis causes painful swallowing (odynophagia) and difficulty swallowing (dysphagia) and is an AIDS-defining condition.

Systemic candidiasis (candidaemia) presents with fever, sepsis, and organ dysfunction and requires urgent hospital treatment.

Cryptococcal meningitis, caused by the yeast Cryptococcus neoformans, is another serious fungal infection treated with fluconazole, typically as consolidation and maintenance therapy following initial treatment with amphotericin B.

How fluconazole works: mechanism of action

Fluconazole belongs to the triazole class of antifungal agents. It targets the fungal enzyme lanosterol 14-alpha-demethylase (CYP51), a cytochrome P450 enzyme essential for the biosynthesis of ergosterol.

Ergosterol is the principal sterol in fungal cell membranes (analogous to cholesterol in human cell membranes) and is critical for maintaining membrane integrity, fluidity, and the function of membrane-bound enzymes.

By inhibiting CYP51, fluconazole prevents the conversion of lanosterol to ergosterol, leading to depletion of ergosterol and accumulation of toxic methylated sterol intermediates.

This disrupts the cell membrane, increases its permeability, and inhibits fungal growth (fungistatic effect). At higher concentrations and in susceptible species, the effect may become fungicidal.

Fluconazole has greater selectivity for fungal CYP51 than for human cytochrome P450 enzymes, which accounts for its relatively favourable safety profile compared with older azoles such as ketoconazole.

However, fluconazole does inhibit several human CYP enzymes (most notably CYP2C9, CYP2C19, and CYP3A4 to a moderate extent), leading to clinically significant drug interactions that must be considered.

Pharmacokinetic profile

Fluconazole has several pharmacokinetic properties that make it particularly useful.

Oral bioavailability exceeds 90%, and absorption is unaffected by food or gastric acidity (unlike itraconazole, which requires an acidic gastric environment for optimal absorption).

It distributes widely into all body compartments, including the cerebrospinal fluid (60 to 80% of plasma levels), saliva, sputum, vaginal secretions, peritoneal fluid, breast milk, and skin.

The plasma half-life is approximately 30 hours, allowing once-daily dosing for most indications and single-dose treatment for uncomplicated vaginal thrush.

Fluconazole is primarily excreted unchanged by the kidneys (approximately 80%), necessitating dose adjustment in patients with impaired renal function on multi-dose regimens.

Clinical evidence and UK prescribing guidance

Fluconazole has been available in the UK since 1988 and has one of the most extensive evidence bases of any antifungal agent.

Randomised controlled trials have demonstrated its efficacy across a wide range of fungal infections.

For uncomplicated vaginal thrush, a single 150 mg oral dose has been shown to be equivalent in efficacy to 7 days of topical clotrimazole, with the convenience of single-dose oral administration often preferred by patients.

For recurrent vulvovaginal candidiasis, the Sobel regimen (150 mg every 72 hours for three doses, followed by 150 mg weekly for 6 months) reduces recurrence rates from approximately 60% to 10% during the maintenance period.

For oropharyngeal candidiasis, fluconazole 50 to 100 mg daily for 7 to 14 days achieves clinical and mycological cure rates exceeding 80%.

For oesophageal candidiasis, fluconazole 200 mg daily is the treatment of choice.

For candidaemia, fluconazole 400 mg daily is an option for haemodynamically stable patients infected with fluconazole-susceptible Candida species, although echinocandins (such as caspofungin, anidulafungin, and micafungin) are now preferred as first-line treatment by many guidelines due to faster fungicidal activity and broader spectrum against Candida glabrata and Candida krusei.

The BNF and NICE Clinical Knowledge Summaries (CKS) on candidiasis provide clear guidance on fluconazole use in UK clinical practice.

For vaginal thrush, CKS recommends oral fluconazole 150 mg as a single dose or topical azole treatment.

For recurrent thrush, referral for vulvovaginal swab culture and sensitivity testing is advised to guide treatment selection.

Fluconazole compared with other antifungal agents

For vaginal thrush, alternatives to oral fluconazole include topical clotrimazole (cream and pessary), econazole, fenticonazole, and miconazole. Topical treatments are preferred in pregnancy and breastfeeding.

Itraconazole 200 mg twice daily for one day is an alternative oral treatment.

For oral thrush, miconazole oral gel is an effective topical option and may be preferred for mild cases.

Nystatin suspension is another topical alternative, though generally less effective than azoles.

For systemic infections, other triazoles (itraconazole, voriconazole, posaconazole, isavuconazole) and echinocandins offer alternative or broader spectrum options. Voriconazole is the first-line treatment for invasive aspergillosis.

Fluconazole has no clinically useful activity against Aspergillus species, and its activity against Candida krusei is intrinsically poor.

Candida glabrata shows increasing rates of fluconazole resistance in some settings. Species identification and antifungal susceptibility testing are important for guiding therapy in invasive infections.

Dosage and administration

Fluconazole capsules should be swallowed whole with water. They may be taken with or without food.

For a single dose (vaginal thrush), take the 150 mg capsule at any convenient time of day.

For multiple-dose regimens, take the dose at approximately the same time each day.

Oral suspension should be shaken well before use and measured with the provided dosing syringe or spoon.

Dose adjustment is required in renal impairment for multiple-dose regimens.

For patients with creatinine clearance of 11 to 50 mL/min, the usual loading dose is given on day 1, followed by half the daily dose on subsequent days.

For patients on haemodialysis, a full dose should be given after each dialysis session. No dose adjustment is needed for a single 150 mg dose.

No hepatic dose adjustment is established, but fluconazole should be used with caution in liver disease, with monitoring of liver function.

Side effects of fluconazole

Common side effects

Headache, nausea, abdominal pain, diarrhoea, and flatulence are the most commonly reported side effects. For a single 150 mg dose, these are usually mild and short-lived.

Rash occurs in up to 1 in 10 patients and is generally mild, but any worsening or blistering of the skin should prompt immediate medical consultation.

Elevated liver enzymes (ALT, AST) may occur, particularly with prolonged therapy, and are usually reversible on discontinuation.

Uncommon and rare side effects

Dizziness, taste disturbance, vomiting, and fatigue are uncommon. Hepatotoxicity, ranging from mild transaminase elevations to fulminant hepatic failure, is rare but has been reported.

The risk is higher in patients with serious underlying conditions and those receiving concomitant hepatotoxic drugs.

Severe cutaneous adverse reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, are very rare but life-threatening.

QT prolongation and associated cardiac arrhythmias (including torsade de pointes) have been reported, particularly at high doses and in patients with other risk factors.

Alopecia (hair thinning or loss) may occur with prolonged high-dose use and is usually reversible. Anaphylaxis and angioedema are extremely rare.

When to seek urgent help

Call 999 or go to A&E if you develop signs of a severe allergic reaction (swelling of face, lips, tongue, or throat; difficulty breathing), extensive skin blistering or peeling, or signs of liver failure (jaundice, confusion, severe abdominal pain).

Call NHS 111 if you develop a spreading rash, persistent nausea or vomiting, dark urine, or symptoms that have not improved 7 days after treatment for thrush.

Report suspected adverse reactions via the Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Drug interactions

Fluconazole is a potent inhibitor of CYP2C9 and a moderate inhibitor of CYP3A4 and CYP2C19. This results in numerous clinically significant drug interactions.

Warfarin: fluconazole increases warfarin exposure and INR, significantly raising the risk of bleeding. Close INR monitoring is essential during and for 1 to 2 weeks after fluconazole therapy.

Statins: co-administration with simvastatin or atorvastatin increases the risk of myopathy and rhabdomyolysis; dose reduction or statin substitution may be required.

Sulfonylureas: fluconazole increases levels of glibenclamide and glipizide, raising the risk of hypoglycaemia; monitor blood glucose closely.

Phenytoin: fluconazole increases phenytoin levels; monitor serum levels and adjust the phenytoin dose. Ciclosporin and tacrolimus: levels are increased by fluconazole; therapeutic drug monitoring is required.

Benzodiazepines: midazolam and triazolam exposure is increased, potentially causing prolonged sedation.

Pregnancy and breastfeeding

Standard low-dose fluconazole (single 150 mg for thrush) has not been associated with an increased risk of birth defects in epidemiological studies.

However, case reports and cohort studies have identified a pattern of congenital anomalies (including skeletal, cardiac, and craniofacial defects) in infants exposed to high-dose fluconazole (400 mg or more daily) during the first trimester.

Fluconazole should be avoided in pregnancy unless the infection is severe or life-threatening and no safer alternative exists.

Topical clotrimazole is the recommended first-line treatment for vaginal thrush in pregnancy. Fluconazole is excreted in breast milk at concentrations similar to plasma.

A single 150 mg dose is generally considered compatible with breastfeeding. For prolonged courses, advice should be sought from a healthcare professional.

Liver disease

Fluconazole should be used with caution in patients with pre-existing liver disease or abnormal liver function tests. Liver function should be monitored during prolonged therapy.

If clinical signs of liver damage develop (jaundice, dark urine, pale stools, fatigue, anorexia), fluconazole must be discontinued immediately.

Cardiac risk

At high doses, fluconazole can prolong the QT interval. Avoid concomitant use with other QT-prolonging drugs (erythromycin, clarithromycin, quinidine, amiodarone, sotalol, haloperidol, domperidone) where possible.

Correct electrolyte disturbances (particularly potassium and magnesium) before starting high-dose therapy. ECG monitoring may be appropriate in high-risk patients.

How to get fluconazole in the UK

For vaginal thrush, fluconazole 150 mg capsules are available from pharmacies without a prescription (Pharmacy, P classification) for women aged 16 to 60 with a previous medical diagnosis of thrush.

The pharmacist will ask screening questions to confirm suitability. Women under 16, over 60, pregnant, breastfeeding, or with recurrent or atypical symptoms should consult a GP.

For all other indications, fluconazole requires a prescription from a GP, hospital specialist, or authorised online prescriber registered with the GPhC.

The NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Preventing recurrent thrush

If you experience frequent episodes of vaginal thrush, several measures may help reduce recurrence alongside medical treatment.

Wear loose-fitting cotton underwear and avoid tight jeans or synthetic fabrics that trap moisture and warmth.

Avoid perfumed soaps, shower gels, vaginal deodorants, and douching, which disrupt the vaginal microbiome. Consider using an emollient wash instead of soap for intimate hygiene.

If you are taking antibiotics, discuss thrush prevention with your prescriber. Ensure good glycaemic control if you have diabetes, as high blood sugar levels promote Candida growth.

Probiotics containing Lactobacillus strains have been studied for thrush prevention, but the evidence remains mixed, and current NICE guidance does not recommend them as standard treatment.

Sources

• Fluconazole 150 mg Capsules, Summary of Product Characteristics (EMC)
• Fluconazole, British National Formulary (BNF)
• NICE CKS: Candida, female genital
• Thrush in men and women, NHS
• MHRA Yellow Card Scheme