Fluconazole is a moderate inhibitor of cytochrome P450 (CYP) isoenzyme 2C9 and 3A4. Fluconazole is also a strong inhibitor of the isozyme CYP2C19. In addition to the observed/documented interactions mentioned below, there is a risk of increased plasma concentration of other compounds metabolized by CYP2C9, CYP2C19 and CYP3A4 coadministered with fluconazole. Therefore caution should be exercised when using these combinations and the patients should be carefully monitored.
The vast majority of formal interaction studies and case reports are related to multiple dose fluconazole use, therefore, the magnitude of the effect of this inhibition on an individual patient after a single dose of fluconazole is hard to predict, particularly in light of the individual variability in the activity of the isoenzymes. Nonetheless, single dose pharmacokinetic studies have demonstrated that the inhibitory action of fluconazole is immediate and leads, dose-dependently, to increased plasma concentrations of the interacting agents.
The enzyme inhibiting effect of fluconazole persists 4-5 days after discontinuation of fluconazole treatment due to fluconazole's long plasma elimination half-life of approximately 30 hours and substantially longer tissue bioavailability (see section 5.2 Pharmacokinetic Properties), therefore these interactions may be clinically relevant following coadministration with drugs that have both a narrow therapeutic window and also act on vital organ systems like the heart and brain or are involved with glucose metabolism.
Oral Anticoagulants (Coumarin-type / Warfarin, Indanedione):
Bleeding events (bruising, epistaxis, gastro-intestinal bleeding, haematuria, and melena) have been reported, in association with increases in prothrombin time in patients receiving fluconazole concurrently with warfarin. During concomitant treatment with fluconazole and warfarin the prothrombin time was prolonged up to 2-fold, probably due to an inhibition of the warfarin metabolism through CYP2C9. In patients receiving coumarin-type or indanedione anticoagulants concurrently with fluconazole the prothrombin time should be carefully monitored. Dose adjustment of the anticoagulant may be necessary.
Sulphonylureas (Chlorpropamide, Glibenclamide, Glipizide, Tolbutamide):
Fluconazole has been shown to prolong the serum half-life of concomitantly administered oral sulphonylureas (e.g. chlorpropamide, glibenclamide, glipizide, tolbutamide) in healthy volunteers.
Frequent monitoring of blood glucose and appropriate reduction of sulfonylurea dose is recommended during coadministration.
Diuretics (Hydrochlorothiazide):
Co-administration of fluconazole and multiple dose hydrochlorothiazide to healthy volunteers during a kinetic interaction study, increased plasma concentrations of fluconazole by 40%. However, although the prescriber should bear this in mind, the fluconazole dose in patients receiving concomitant diuretics should not need to be altered.
Pimozide, Quinidine, Erythromycin:
Coadministration of fluconazole and other drugs such as pimozide, quinidine and erythromycin is contraindicated. Fluconazole can cause changes in the metabolism of these drugs, which can lead to increased plasma levels with potential risk of cardiotoxicity (QT prolongation and torsades de pointes).
Antiarrhythmics (Amiodarone):
Concomitant administration of fluconazole with amiodarone may increase QT prolongation. Therefore, caution should be taken when both drugs are combined, notably with high doses fluconazole (800 mg).
Hypnotic (Lemborexant):
Fluconazole increases Lemborexant Cmax and AUC by approximately 1.6 and 4.2-fold respectively which is expected to increase risk of adverse reactions, such as somnolence. Therefore concomitant use of Lemborexant should be avoided.
Hypnotic (Lemborexant):
Fluconazole increases Lemborexant Cmax and AUC by approximately 1.6 and 4.2-fold respectively which is expected to increase risk of adverse reactions, such as somnolence. Therefore concomitant use of Lemborexant should be avoided.
Antimalarials (Halofantrine):
Fluconazole can also lead to increased levels of halofantrine (via inhibitory effect on CYP3A4) with potential risk of cardiotoxicity. This combination should be avoided (see section 4.4).
Antipsychotics (Lurasidone):
Moderate inhibitors of CYP3A4 such as fluconazole may increase lurasidone plasma concentrations and so concomitant use should be avoided. If concomitant use cannot be avoided, a reduced dose of lurasidone as instructed in the lurasidone prescribing information should be used.
Antipsychotics (Lurasidone):
Moderate inhibitors of CYP3A4 such as fluconazole may increase lurasidone plasma concentrations and so concomitant use should be avoided. If concomitant use cannot be avoided, a reduced dose of lurasidone as instructed in the lurasidone prescribing information should be used.
Benzodiazepines (Midazolam, Triazolam):
Following oral administration of midazolam, fluconazole resulted in substantial increases in midazolam concentrations and psychomotor effects. Concomitant intake of fluconazole 200 mg and midazolam 7.5 mg orally increased the midazolam AUC and half-life 3.7-fold and 2.2-fold, respectively. Fluconazole 200 mg daily given concurrently with triazolam 0.25 mg orally increased the triazolam AUC and half-life 4.4-fold and 2.3-fold, respectively. Potentiated and prolonged effects of triazolam have been observed at concomitant treatment with fluconazole.
If concomitant benzodiazepine therapy is necessary in patients being treated with fluconazole, consideration should be given to decreasing the benzodiazepine dose, and the patients should be appropriately monitored.
Cystic fibrosis transmembrane conductance regulator (CFTR) potentiator (Ivacaftor):
A reduction of the ivacaftor (alone or combined with drugs in the same therapeutic class) dose is necessary as instructed in the ivacaftor prescribing information due to increased exposure when co-administered with fluconazole.
HMG CoA reductase inhibitors (Atorvastatin, Simvastatin, Fluvastatin):
The risk of myopathy and rhabdomyolysis increases (dose-dependent) when fluconazole is coadministered with HMG-CoA reductase inhibitors metabolised through CYP3A4, such as atorvastatin and simvastatin, or through CYP2C9, such as fluvastatin (decreased hepatic metabolism of the statin). If concomitant therapy is necessary, the patient should be observed for symptoms of myopathy and rhabdomyolysis and creatine kinase should be monitored. HMG-CoA reductase inhibitors should be discontinued if a marked increase in creatine kinase is observed or myopathy/rhabdomyolysis is diagnosed or suspected. Lower doses of HMG-CoA reductase inhibitors may be necessary as instructed in the statins prescribing information.
Antiepileptics (Phenytoin, Carbamazepine):
Levels of phenytoin may increase to a clinically significant degree during co-administration with fluconazole. Phenytoin levels should be monitored and the phenytoin dose adjusted to maintain therapeutic levels if co-administration is necessary.
Fluconazole inhibits the metabolism of carbamazepine and an increase in serum carbamazepine of 30% has been observed. There is a risk of developing carbamazepine toxicity, therefore dose adjustment of carbamazepine may be necessary.
Oral Contraceptives (Ethinylestradiol, Levonorgestrel):
Studies on the use of combined oral contraceptives with multiple doses of fluconazole have been performed. No relevant effects on hormone levels occurred during a study with fluconazole 50mg, whilst the AUCs of ethinylestradiol and levonorgestrel were increased by 40% and 24% respectively during a study with fluconazole 200mg. It is therefore considered that multiple dose fluconazole is unlikely to affect the efficacy of the combined oral contraceptive.
Anti-infectives (Rifampicin, Rifabutin):
A 25% decrease in the AUC and 20% shorter half-life of fluconazole occurred when fluconazole and rifampicin were administered concomitantly. An increase in the fluconazole dose should be considered in patients receiving concomitant rifampicin.
Fluconazole increases serum concentrations of rifabutin, leading to increase in the AUC of rifabutin up to 80%. There have been reports of uveitis in patients to whom fluconazole and rifabutin were coadministered. In combination therapy, symptoms of rifabutin toxicity should be taken into consideration.
Angiotensin II Antagonists (Losartan):
CYP2C9 and CYP3A4 are involved in the metabolism of losartan to its active carboxylic acid metabolite E-3174 that is responsible for most of the angiotensin II receptor antagonism that occurs with losartan therapy. Fluconazole was shown to significantly inhibit the conversion of losartan to this metabolite. Monitoring of patients for continued control of their hypertension is recommended.
Antidepressants (Amitriptyline and Nortriptyline):
Fluconazole increases the effect of amitriptyline and nortriptyline. Dose of amitriptyline/ nortriptyline should be adjusted, if necessary.
Analgesics/Anaesthetics (Alfentanil, Fentanyl, Methadone):
Coadministration of fluconazole may cause decreased clearance of alfentanil, fentanyl or methadone and subsequent increased or prolonged opioid effects (CNS depression, respiratory depression). Dose adjustment may be required.
Xanthines (Theophylline):
Use of fluconazole 200mg for 14 days showed an 18% decrease in the mean plasma clearance of theophylline. Patients who require high doses of theophylline or who may be at increased risk of theophylline toxicity should be monitored for signs of theophylline toxicity when fluconazole is co-administered. The therapy should be modified if signs of toxicity occur.
Antihistamines (Terfenadine, Astemizole):
One study with terfenadine and fluconazole 200mg daily did not show a prolongation in the QTc interval. Use of fluconazole (taken in multiple doses of 400mg and 800mg per day) and terfenadine concomitantly, significantly increased plasma levels of terfenadine. Spontaneous reports of palpitations, tachycardia, dizziness and chest pains have occurred in patients taking fluconazole and terfenadine concomitantly where the relationship of the reported adverse events to drug therapy or underlying medical condition is uncertain. It is recommended that terfenadine and fluconazole should not be administered concomitantly due to the potential seriousness of such an interaction (see section 4.3).
Astemizole taken concomitantly with fluconazole may be associated with elevations in serum levels of this drug in patients, which can lead to QT prolongation and torsades de pointes. Coadministration of fluconazole and astemizole is contraindicated (see section 4.3).
Propulsives (Cisapride):
Cardiac events including torsades de pointes have been reported in patients receiving fluconazole and cisapride concomitantly. A controlled study found that concomitant fluconazole 200 mg once daily and cisapride 20 mg four times a day yielded a significant increase in cisapride plasma levels and prolongation of QTc interval. Co-administration of cisapride is contra-indicated in patients receiving fluconazole (see section 4.3).
Antivirals (Zidovudine, Saquinavir):
Fluconazole increases Cmax and AUC of zidovudine by 84% and 74%, respectively, due to an approx. 45% decrease in oral zidovudine clearance. The half-life of zidovudine was likewise prolonged by approximately 128% following combination therapy with fluconazole. Patients receiving this combination should be monitored for the development of zidovudine-related adverse reactions.
Fluconazole increases the AUC and Cmax of saquinavir with approximately 50% and 55% respectively, due to inhibition of saquinavir's hepatic metabolism by CYP3A4 and inhibition of P-glycoprotein.
Dose adjustment of these drugs may be required.
Non-Steroidal Anti-inflammatory drugs (Celecoxib, Flurbiprofen, Ibuprofen, Naproxen, Lornoxicam, Meloxicam, Diclofenac):
Fluconazole may increase the systemic exposure of non-steroidal anti-inflammatory drugs. Adjustment of dose during concomitant treatment may be required.
Immuno-suppressants (Ciclosporin, Tacrolimus, Sirolimus, Tofacitinib):
Fluconazole significantly increases the concentration and AUC of ciclosporin. During concomitant treatment with fluconazole 200 mg daily and ciclosporin (2.7 mg/kg/day) there was a 1.8 fold increase in ciclosporin AUC. This combination may be used by reducing the dose of ciclosporin depending on ciclosporin concentration.
Increased serum levels of tacrolimus (when orally administered) and sirolimus have been reported in patients receiving fluconazole and these drugs concomitantly, potentially due to inhibition of their metabolism. Increased levels of tacrolimus have been associated with nephrotoxicity. Dose of tacrolimus or sirolimus should be adjusted.
Exposure of tofacitinib is increased when tofacitinib is co-administered with fluconazole therefore, it is recommended to reduce tofacitinib dose to 5 mg once daily.
Kinase Inhibitors (Ibrutinib, Abrocitinib)
Moderate inhibitors of CYP3A4 such as fluconazole increase plasma ibrutinib concentrations and may increase risk of toxicity. If the combination cannot be avoided, reduce the dose of ibrutinib to 280 mg once daily (two capsules) for the duration of the inhibitor use and provide close clinical monitoring.
Fluconazole (inhibitor of CYP2C19, 2C9, 3A4) increased exposure of abrocitinib active moiety by 155%. If co-administered with fluconazole, adjust the dose of abrocitinib as instructed in the abrocitinib prescribing information.
Poly(ADP-ribose) polymerase (PARP) Inhibitor (Olaparib)
Fluconazole increases olaparib plasma concentrations therefore, concomitant use is not recommended. If the combination cannot be avoided limit the dose of olaparib to 200 mg twice daily.
Studies show that when fluconazole is taken orally with food, cimetidine, antacids or following total body irradiation for bone marrow transplantation, the absorption of fluconazole is not significantly impaired.
Selective Vasopressin V2-Receptor Antagonist (Tolvaptan)
Exposure to tolvaptan is significantly increased (200% in AUC; 80% in Cmax) when tolvaptan, a CYP3A4 substrate, is co-administered with fluconazole, a moderate CYP3A4 inhibitor, with risk of significant increase in adverse reactions particularly significant diuresis, dehydration and acute renal failure. In case of concomitant use, the tolvaptan dose should be reduced as instructed in the tolvaptan prescribing information and the patient should be frequently monitored for any adverse reactions associated with tolvaptan.