Fluconazole dosage, forms, and strengths

Fluconazole (Diflucan) is a medication used to treat fungal infections that affect the skin, digestive system, blood, nails, brain, urinary tract, and genitals. It belongs to a drug class called triazole antifungals. It is effective against more types of fungi compared to other triazoles. While it is a very common and useful medication, fluconazole interacts with many medications. This article will review important details about fluconazole dosages, drug interactions, and how to use it safely.

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Fluconazole forms and strengths

Fluconazole is available as a tablet or as a liquid suspension under the brand name Diflucan or in the generic form. It is also available as an intravenous injection.

• Tablets: 50 mg, 100 mg, 150 mg, 200 mg

• Suspension: 10 mg/ mL, 40 mg/ mL

• Injection: 2 mg/mL

Fluconazole dosage for adults

Fluconazole is commonly used to treat candida infections but it’s also effective against other types of molds and fungi, including cryptococcus neoformans, Blastomyces dermatitidis, coccidioides immitis, Histoplasma capsulatum, Malassezia furfur, prototheca species, dematiaceous molds, and dermatophytes. Below are some common infections that fluconazole may be prescribed to treat:

Fluconazole dosage for esophageal and oropharyngeal candidiasis

Fluconazole is commonly used to treat yeast infections of the mouth or throat (thrush). The typical dose is 50 to 200 mg on day one, followed by 50 to 400 mg depending on whether the infection is in the mouth (oral), just behind the mouth (oropharyngeal), or lower in the esophagus (esophageal). Yeast infections of the throat typically resolve within several days, but treatment should be continued for two to three weeks, (at least two weeks following resolution of symptoms).

Fluconazole dosage for candidemia

Candidemia is a type of systemic candida infection, in which candida is present in the blood. It is the most common fungal bloodstream infection in hospitalized patients. It is diagnosed by performing a blood culture, which will also determine how effective fluconazole will be against the infection. Based on the severity of the infection and the results from the blood culture, a different antifungal such as an echinocandin may be needed. An initial loading dose of 800 mg is given orally or by intravenous injection, followed by 400 mg twice daily for two days, then a daily dose of 400 mg thereafter. The duration of fluconazole therapy is at least two weeks after blood cultures show clearance of the bloodstream infection.

Fluconazole dosage for cryptococcal meningitis

Cryptococcal meningitis is diagnosed by obtaining a culture of the cerebral spinal fluid (CSF) via a lumbar puncture. In non-HIV infected patients, fluconazole is not typically used for the beginning phase of therapy (induction therapy). Rather, amphotericin B and flucytosine are the antifungals of choice.  As alternative options, fluconazole 800 mg plus amphotericin B for two weeks may be used for some patients for induction therapy. This may be followed by consolidation therapy with fluconazole 400 to 800 mg daily for eight weeks, followed by maintenance therapy with fluconazole 200 to 400 mg daily for six to 12 months. 

Another alternative option is fluconazole 1200 mg daily by itself for at least 10 weeks for induction therapy, followed by fluconazole 200 to 400 mg daily as maintenance therapy.

Fluconazole dosage for prevention of candidiasis in BMT patients

The recommended fluconazole dosage for preventing candidiasis in patients undergoing bone marrow transplantation is 400 mg daily. In patients who are likely to have severe neutropenia (neutrophils fewer than 500 per cubic millimeter), fluconazole therapy should begin several days before the onset of neutropenia and continued for one week after neutrophil count returns to 1,000 cells per cubic mm or higher.

Fluconazole dosage for urinary tract infections

For symptomatic urinary tract candida infections, fluconazole doses ranging from 50 to 400 mg daily for one to two weeks (depending on the location within the urinary tract, and the presence of complicating factors) have been shown to be effective.

Fluconazole dosage for vaginal candidiasis

Vaginal candidiasis (vaginal yeast infection) is one of the most common uses for fluconazole. In patients with uncomplicated disease (neither pregnant, immunocompromised, nor recurring vaginal candidiasis), a one-day treatment is sufficient. Patients with complicated disease may require longer therapy, typically fluconazole every three days for three doses. Recurrent disease requires weekly fluconazole for six months. Finally, pregnant patients should not use oral fluconazole due to its potential for harm to the fetus. Rather, a seven-day course of intravaginal therapy should be used.

Fluconazole dosage for coccidioidomycosis

Coccidioidomycosis, also known as valley fever, is caused by the coccidioides fungus. Infection usually begins in the lungs by inhaling wind-borne spores. The disease may be mild or severe, even life-threatening if the central nervous system becomes infected. Some infections may be mild are resolve without any therapy. For more complicated infections, fluconazole is generally the treatment of choice. A dosage of 400 mg daily is used initially, and therapy may be escalated to 800 to 1200 mg daily if clinical outcomes do not improve with 400 mg daily. The duration of treatment is based on the resolution of symptoms and the location of the infection.

Fluconazole dosage for nail onychomycosis

Candida infections of the toenail or fingernail involve discoloration, thickening, and separation of the nails from the nail bed, and maybe treated with oral fluconazole (although many antifungal treatment options exist). Oral antifungals are generally more effective than topical therapies such as ciclopirox 8% nail lacquer. The fluconazole dose is 100 to 450 mg taken once weekly. The duration of therapy is three to six months for fingernail infections and six to 12 months for toenail infections.

RELATED: Home remedies for toenail fungus

Fluconazole dosage for children

A general guideline for converting adult dosages into pediatric dosages is listed below:

* 1 kg is equal to 2.2 lbs.

The fluconazole dose for pediatric patients should not exceed 600 mg per day. 

Fluconazole dosage restrictions

You should not take Diflucan (fluconazole) if you have had an allergic reaction (rash, hives, swelling of the face and throat) to its active ingredient or any component of Diflucan tablets or suspension in the past.

Diflucan should be administered with caution to patients with liver dysfunction. There have been rare reports of serious liver toxicity in patients taking Diflucan, primarily in patients with serious underlying medical conditions. In most cases, liver injury from Diflucan is reversed once Diflucan therapy is stopped. Diflucan should be discontinued if clinical signs and symptoms consistent with liver disease develop after beginning treatment.

Exfoliative skin disorders during treatment with Diflucan have been reported. Patients with deep-seated fungal infections who develop rashes during treatment with Diflucan should be monitored closely and the drug discontinued if lesions progress.

Diflucan should not be used in pregnant women during the first trimester. There is potential for fetal harm since no adequate and well-controlled clinical trials of Diflucan in pregnant women exist to date. There have been case reports describing a pattern of distinct congenital anomalies in infants exposed to high dose maternal fluconazole (400 to 800 mg/day) during most or all of the first trimester. Effective contraceptive measures should be used in women of child-bearing age who are being treated with Diflucan 400 to 800 mg/day and should until approximately one week after the final dose.

Patients with a history of heart disease or arrhythmia, including congenital long QT syndrome, QT prolongation, torsades de pointes, ventricular arrhythmias, slow heart rate (bradycardia), recent heart attack (myocardial infarction), congestive heart failure, or other heart diseases should use caution while taking fluconazole. Fluconazole is known to increase the QT interval (a measure of time between stages of heart contraction), which can precipitate arrhythmias or other cardiovascular events.

The use of fluconazole in older patients or patients with kidney dysfunction (low creatinine clearance) requires additional caution as elimination of fluconazole is highly dependent upon renal (kidney) function. Adverse effects of Diflucan may be increased in older adults or patients with kidney impairment.

Fluconazole dosage for pets

Fluconazole is used to treat yeast infections in cats, dogs, and other small mammals. While fluconazole does not have FDA approval for this use, it is effective and commonly prescribed for pets with yeast infections of the skin, nail beds, urinary tract, or other organs. A starting dose of 10 mg/kg twice daily for dogs, or 50-100 mg per day in cats, is recommended to treat fungal infections.

How to take fluconazole

• Read and follow the patient instructions that come with this medicine. Talk to your healthcare provider or pharmacist if you have any questions.

• Fluconazole tablets and oral suspension can be taken with or without food.

• Tablets may be cut or crushed if needed.

• Shake the oral suspension well before using. Store reconstituted suspension between 41 and 86 degrees Fahrenheit and discard unused portions after two weeks.

• Use the dosing syringe provided or use a medicine dose-measuring device (not a kitchen spoon).

• Store fluconazole at room temperature away from moisture and heat. Do not freeze.

• Use fluconazole for the full prescribed length of time, even if your symptoms quickly improve. Skipping doses can increase your risk of infection that is resistant to medication. Fluconazole will not treat a viral infection such as the flu or a common cold.

Fluconazole dosage FAQs

How long does it take fluconazole to work?

Oral fluconazole reaches its peak concentration in the bloodstream about two hours after being taken by mouth. The time it takes fluconazole to alleviate symptoms depends on the dosing regimen and the location of the infection, since fluconazole distributes to some areas faster than others. The time to symptom relief can range from one hour to nine days, with an average time of one to three days.

How long does fluconazole stay in your system?

Fluconazole follows zero-order kinetics, meaning that the drug is eliminated at a constant rate, regardless of the amount left in your system. This means that higher doses will take longer to eliminate. It is mainly excreted in the urine, so patients with impaired kidney function are at higher risk of overdose compared to those with healthy kidneys. Overall, the time it takes to eliminate fluconazole is patient-dependent but is generally longer than many other drugs. For example, it often takes adults with normal kidney function six to nine days to eliminate fluconazole following a typical dose.

What happens if I miss a dose of fluconazole?

In the event of a missed dose, take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

How long can you take fluconazole?

The duration of fluconazole therapy is dependent upon the type of infection being treated. Some types of infections, such as vaginal candidiasis, may only require a one-time dose. On the other end of the spectrum, coccidioidal meningitis, the most serious complication of coccidioidomycosis (valley fever), may require indefinite treatment. Fluconazole is commonly used to treat urinary tract infections for which the duration of therapy is typically two weeks. A healthcare provider will monitor symptoms and/or lab results to determine when the infection is cured.

What interacts with fluconazole?

Many drugs interact with fluconazole, and many drugs will not their dose adjusted to account for this. It is very important to share a list of current medications with a healthcare provider while taking any antifungal drug. 

Fluconazole decreases the activity of the enzymes CYP2C9, CYP2C19, and CYP3A4, found in the liver. Because these enzymes help metabolize many other drugs, taking fluconazole can cause other drugs to be metabolized more slowly. This increases the levels of those drugs. 

Fluconazole has also been associated with prolongation of the QT interval on the electrocardiogram. Patients may need to avoid taking fluconazole with other drugs that also prolong the QT interval, due to the addictive nature of this side effect. Additionally, some drugs that prolong the QT interval (such as amiodarone) may have their effects amplified by fluconazole due to its effect on liver enzymes that metabolize drugs. In these cases, the risk of QT prolongation is even more severe.

Fluconazole should be avoided in patients who are taking the following:

• Artemether/lumefantrine

• Cidaspride

• Cisapride

• Disopyramide

• Dofetilide

• Dronedarone

• Eliglustat

• Eplerenone

• Erythromycin

• Felodipine

• Flibanserin

• Irinotecan

• Lomitapide

• Lonafarnib

• Lovastatin

• Lurasidone

• Methadone

• Midazolam

• Nisoldipine

• Pimozide

• Quinidine

• Quinine

• Ranolazine

• Ribociclib

• Simvastatin

• Thioridazine

• Tramadol

• Triazolam

• Zidovudine

Certain drugs may need dose adjustments when taken with fluconazole since it is an inhibitor of liver enzymes that metabolize drugs. Examples include amiodarone, carbamazepine, cyclosporine, glipizide, tacrolimus, theophylline, phenytoin, warfarin, and others. This is not an exhaustive list of all drugs that can potentially interact with fluconazole. It is best to consult with a doctor or pharmacist about potential interactions with other medications you are taking.

What happens when you mix fluconazole and alcohol?

It is safe to eat and drink normally while taking fluconazole. There are no known interactions between alcohol and fluconazole. However, since both fluconazole and alcohol can have negative effects on the liver, it is advisable for patients with liver impairment (i.e. jaundice, hepatitis) to avoid alcohol, especially while taking fluconazole. Another important consideration is that excessive alcohol use can weaken the immune system and worsen candida infections, potentially working against the effects of fluconazole.

Is it safe to take fluconazole during pregnancy?

It is not safe to take fluconazole during the first trimester of pregnancy. After the first trimester, some risk of harm to the fetus is possible, and use should be based on a risk vs. benefit assessment by a clinician. 

Fluconazole may be used while breastfeeding, as there is no known risk of infant harm from exposure to fluconazole through breast milk. However, the infant may experience side effects such as GI upset and diarrhea.

Related resources for fluconazole dosages:

• Alcohol and the immune system

• Clinical practice guidelines for the management of cryptococcal disease: 2010 update by the infectious diseases society of America

• Coccidioidal meningitis

• Diflucan prescribing information

• Exploring valley fever

• The fungus among us

• Fluconazole

• Fungemia candidiasis

• IDSA updates guideline on treatment of candidiasis

• Clinical pharmacokinetics and outcomes of oral fluconazole therapy in dogs and cats with naturally occurring fungal disease

• Onychomycosis: Current trends in diagnosis and treatment