In addition to the interactions given below, there is a risk of elevated serum concentrations of other drugs metabolised via CYP2C9 and CYP3A4 with concomitant administration of fluconazole. Fluconazole is a potent inhibitor of cytochrome P450 (CYP) isoenzyme 2C9 and a moderate inhibitor of CYP3A4. Fluconazole is also an inhibitor of the isozyme CYP2C19 Therefore caution should always be observed during combination therapy with medications such as these and the patient closely monitored. The effects may persist for 4-5 days due to the long half life of fluconazole.
Concomitant use of the following other medicinal products is contraindicated
Astemizole (CYP3A4-substrate):
Astemizole overdoses have led to prolonged QT interval a severe ventricular arrhythmia, torsade de pointes and cardiac arrest. Concomitant administration of astemizole and fluconazole is contraindicated due to the potential for serious, potentially fatal, cardiac effects.
Cisapride (CYP3A4-substrate):
Cardiovascular effects, including torsade de pointes, have been reported in patients having received concomitant treatment with fluconazole and cisapride. In one controlled study, where 200 mg fluconazole was administered once daily concomitantly with cisapride 20 mg four times daily, a significant increase in plasma levels of cisapride and prolongation of the QTc-interval where achieved. Concurrent treatment with cisapride and fluconazole is contraindicated (see 4.3 Contraindications).
Terfenadine (400 mg fluconazole and higher; CYP3A4-substrate):
Serious cardiac arrhythmias, secondary to prolonged QTc- interval, have occurred in patients treated with anti-fungal medications such as triazolic compounds and terfenadine. Concomitant treatment with 200 mg fluconazole daily showed no prolongation of the QTc-interval. With doses of 400 mg and 800 mg fluconazole daily, the plasma concentration of terfenadine increased significantly. Concomitant treatment with fluconazole 400 mg per day or higher dose is contraindicated. With concomitant treatment with doses below 400 mg per day, the treatment should be closely monitored.
Pimozide and Quinidine:
Although not studied in vitro or in vivo, concomitant administration of fluconazole with pimozide may result in inhibition of pimozide metabolism. Increased pimozide plasma concentrations can lead to QT prolongation and rare occurrences of Torsades de Pointes. Co-administration of fluconazole and pimozide is contraindicated (see section 4.3).
Erythromycin:
Concomitant use of fluconazole and erythromycin has the potential to increase the risk of cardiotoxicity (prolonged QT interval, torsades de pointes) and consequently sudden heart death. Co-administration of fluconazole and erythromycin is contraindicated (see section 4.3).
Halofantrine:
Fluconazole can increase halofantrine plasma concentration due to an inhibitory effect on CYP3A4. Concomitant use of fluconazole and halofantrine has the potential to increase the risk of cardiotoxicity (prolonged QT interval, torsades de pointes) and consequently sudden heart death. This combination should be avoided (see section 4.4).
Concomitant use of the following other medicinal products lead to precautions and dose adjustments
The effects of other medicinal products on fluconazole:
Hydrochlorothiazide:
In a pharmacokinetic interaction study, co-administration of multiple-dose hydrochlorothiazide to healthy volunteers receiving fluconazole increased plasma concentration of fluconazole by 40%. An effect of this magnitude should not necessitate a change in the fluconazole dose regimen in subjects receiving concomitant diuretic.
Rifampicin (CYP450-inducers):
Concomitant treatment with fluconazole (200 mg) and rifampicin (600 mg daily) reduced AUC for fluconazole by 23 % in healthy volunteers.
An increase in the dose of fluconazole should be considered in combination treatment.
Concomitant use of the following other medicinal products cannot be recommended
Amiodarone: concomitant administration of fluconazole with amiodarone may increase QT prolongation. Therefore, caution should be taken when both drugs are combined, notably with high dose fluconazole (800 mg).
The effects of fluconazole on other medicinal products:
Alfentanil (CYP3A4-substrate):
In concomitant treatment with fluconazole (400 mg) and intravenous alfentanil (20 µg/kg) in healthy volunteers, AUC10 – increased twofold and clearance decreased by 55 % for alfentanil, probably through inhibition of CYP3A4. The combination may require dose adjustment.
Amphotericin B:
In-vitro and in-vivo animal studies have found antagonism between amphotericin B and azole derivatives. The mechanism of action of imidazoles is to inhibit ergosterol synthesis in fungal cell membranes. Amphotericin B acts by binding to sterols in the cell membrane and changing membrane permeability. Clinical effects of this antagonism are to date unknown. A similar effect may occur with amphotericin B cholesteryl sulfate complex.
Concurrent administration of fluconazole and amphotericin B in infected normal and immunosuppressed mice showed a small additive antifungal effect in systemic infection with C.albicans, no interaction in intracranial infection with Cryptococcus neoformans.
Amitriptyline (CYP2D6-substrate):
Several case histories have described the development of elevated amitriptyline concentrations and signs of tricyclic toxicity when amitriptyline is used in combination with fluconazole. Concomitant infusion of fluconazole and nortriptyline, the active metabolite of amitriptyline, has been reported to lead to increased nortriptyline levels. Due to the risk of amitriptyline toxicity, monitoring of amitriptyline levels should be considered with dose adjustment where indicated.
Anticoagulants
In post-marketing experience, as with other azole antifungals, bleeding events (bruising, epistaxis, gastrointestinal 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.
Benzodiazepines (CYP3A4-substrate):
Fluconazole may inhibit the metabolism of benzodiazepines metabolised via CYP3A4, e.g. midazolam and triazolam. In concomitant oral single dose treatment with fluconazole (400 mg) and midazolam (7.5 mg) AUC increased 3.7 times and the half life of midazolam 2.2 times. The combination should be avoided. Where concomitant treatment is considered necessary, a reduction in the dose of midazolam should be considered and the patient monitored closely In concomitant treatment with fluconazole (100 mg daily for 4 days) and triazolam (0.25 mg) the AUC and half-life of triazolam increased respectively 2.5 and 1.8 times. Prolonged and enhanced effects from triazolam have been observed. The combination may require reduction in the dose of triazolam.
Calcium channel antagonists (CYP3A4-substrates):
Some dihydropyridine calcium channel antagonists, including nifedipine, isradipine, nicardipine, amlodipine, and felodipine, are metabolised via CYP3A4. Literature reports have documented substantial peripheral oedema and/or elevated calcium antagonist serum concentrations during concurrent use of itraconazole and felodipine, isradipine, or nifedipine. An interaction might occur also with fluconazole. Frequent monitoring for adverse events is recommended.
Carbamazepine (CYP3A4-substrate):
Carbamazepine is metabolized by isozyme CYP3A4. Fluconazole is thus likely to cause carbamazepine toxicity, probably due to inhibition of isozyme CYP3A4. Dose adjustment of carbamazepine may be necessary depending on concentration measurements/effect.
Celecoxib (CYP2C9-substrate):
In concomitant treatment with fluconazole (200 mg daily) and celecoxib (200 mg), Cmax and AUC for celecoxib increased by 68 % and 134 % respectively.
Halving the dose of celecoxib is recommended in combination therapy with fluconazole.
Cyclophospamide:
Combination therapy with cyclophosphamide and fluconazole results in an increase in serum bilirubin and serum creatinine. The combination may be used while taking increased consideration to the risk of increased serum bilirubin and serum creatinine.
Fentanyl:
One fatal case of fentanyl intoxication due to possible fentanyl fluconazole interaction was reported. Furthermore, it was shown in healthy volunteers that fluconazole delayed the elimination of fentanyl significantly. Elevated fentanyl concentration may lead to respiratory depression. Patients should be monitored closely for the potential risk of respiratory depression. Dosage adjustment of fentanyl may be necessary.
Ciclosporin (CYP3A4-substrate):
Clinically significant interactions between ciclosporin and fluconazole have been observed at doses of fluconazole of 200 mg and higher. In concomitant treatment with 200 mg fluconazole daily and ciclosporin (2.7 mg/kg/day), AUC for ciclosporin increased approximately 1.8 times and clearance was reduced by approximately 55 %. The plasma concentration of ciclosporin should be monitored in concomitant treatment with fluconazole.
However, in another multiple dose study with 100mg daily, fluconazole did not affect ciclosporin levels in patients with bone marrow transplants. Ciclosporin plasma concentration monitoring in patients receiving fluconazole is recommended.
Everolimus:
Although not studied in vivo or in vitro, fluconazole may increase serum concentrations of everolimus through inhibition of CYP3A4.
Didanosine:
Coadministration of didanosine and fluconazole appears to be safe and has little effect on didanosine pharmacokinetics or efficacy. However, it is important to monitor fluconazole response. It may be advantageous to stagger fluconazole dosing to a time prior to didanosine administration.
HMG-CoA-reductase-inhibitors (CYP2C9- or CYP3A4-substrate):
The risk of myopathy and rhabdomyolysis increases when fluconazole is administered concomitantly with HMG-CoA-reductase inhibitors that are metabolised via CYP3A4, e.g. atorvastatin and simvastatin, or via CYP2C9, such as fluvastatin. For fluvastatin an individual increase of up to 200% in the area under the curve (AUC) can occur as a result of interaction between fluvastatin and fluconazole. An individual patient using fluvastatin 80 mg daily may be exposed to considerable fluvastatin concentrations if treated with high doses of fluconazole. Caution should be observed where concomitant treatment with fluconazole and HMG-CoA-reductase-inhibitors is considered necessary.
The combination may require dose reduction of the HMG-CoA reductase inhibitors. The patient should be observed with regard to signs of myopathy or rhabdomyolysis and creatine kinase concentrations (CK). The HMG-CoA treatment should be stopped if CK concentrations show a marked increase or if myopathy or rhabdomyolysis is diagnosed or suspected.
Losartan (CYP2C9-substrate):
Fluconazole inhibits the conversion of losartan to its active metabolite (E-3174), which is responsible for the most of the angiotensin II receptor antagonism that occurs with losartan therapy. Concomitant treatment with fluconazole might lead to increased concentrations of losartan and decreased concentrations of the active metabolite. It is recommended that patients receiving the combination be monitored for continued control of their hypertension.
Methadone:
There are reports of a reinforced impact of methadone after concomitant administration of fluconazole and methadone. A pharmacokinetics study showed increased AUC of methadone (35% on average). Dose adjustment of methadone may be necessary.
Non-steroidal anti-inflammatory drugs:
The Cmax and AUC of flurbiprofen was increased by 23% and 81%, respectively, when co-administered with fluconazole compared to administration of flurbiprofen alone. Similarly, the Cmax and AUC of the pharmacologically active isomer [S-(+)-ibuprofen] was increased by 15% and 82%, respectively, when fluconazole was co-administered with racemic ibuprofen (400mg) compared to administration of racemic ibuprofen alone.
Although not specifically studied, fluconazole has the potential to increase the systemic exposure of other NSAIDs that are metabolized by CYP2C9 (e.g. naproxen, lornoxicam, meloxicam, diclofenac). Frequent monitoring for adverse events and toxicity related to NSAIDs is recommended. Adjustment of dose of NSAIDs may be needed.
Oral contraceptive agents (CYP3A4-substrate):
In a kinetic study with combined oral contraceptives and 50 mg fluconazole daily, hormonal levels were not affected. With 200 mg fluconazole daily, AUC for ethynylestradiol increased by 40 % and levonorgestrel by 24 %.
In a 300 mg daily fluconazole study, the AUCs of ethinyl estradiol and norethindrone were increased by 24% and 13% respectively.
Thus multiple dose use of fluconazole at these doses is unlikely to have an effect on the efficacy of the combined oral contraceptive.
Phenytoin (CYP2C9-substrate):
Concomitant, repeated treatment with 200 mg fluconazole and 250 mg phenytoin intravenously increased AUC24 for phenytoin by 75 % and Cmin by 128 %. In combination treatment, plasma phenytoin concentrations should be monitored and the dose adjusted.
Prednisone (CYP3A4-substrate):
A liver transplant recipient receiving prednisone experienced an Addisonian crisis when a three-month course of fluconazole was discontinued. The withdrawal of fluconazole likely caused an increase in CYP3A4 activity, leading to an increase in the degradation of prednisone. Patients receiving long-term therapy with fluconazole and prednisone should be closely monitored for signs of adrenal insufficiency when fluconazole is withdrawn.
Rifabutin (CYP3A4-substrate):
In concomitant treatment with fluconazole and rifabutin, the serum concentrations of rifabutin increased. Uveitis has been reported. Patients undergoing concomitant treatment should be monitored closely.
Saquinavir:
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. Interaction with saquinavir/ritonavir has not been studied and might be more marked. Dose adjustment of saquinavir may be necessary.
Sirolimus and tacrolimus (3A4-substrate):
In concomitant oral treatment with fluconazole and tacrolimus (0.15 mg/kg twice daily) the plasma concentration trough level of tacrolimus increased 1.4 and 3.1 times with a daily fluconazole dose of 100 mg and 200 mg respectively. Nephrotoxicity has been reported. Even though no interaction studies have been performed with fluconazole and sirolimus, a similar interaction can be anticipated. In concomitant treatment with fluconazole and tacrolimus or sirolimus, patients should be closely monitored and an adjustment in dose considered.
Sulphonylureas (CYP2C9-substrate):
Fluconazole has displayed prolonged half-life in serum for concomitantly administered sulphonylureas (glibencamide, glipizide, chlorpropamide and tolbutamide) in healthy volunteers. Fluconazole may be administered to diabetics together with sulphonylureas, but the risk of hypoglycemia should be considered. Blood glucose levels should be closely monitored.
Theophylline:
In a placebo-controlled interaction study, the administration of fluconazole 200mg for 14 days resulted in an 18% decrease in the mean plasma clearance of theophylline. Patients who are receiving high doses of theophylline or who are otherwise at increased risk for theophylline toxicity should be observed for signs of theophylline toxicity while receiving fluconazole, and the therapy modified appropriately if signs of toxicity develop.
Vinca alkaloids:
Although not studied, fluconazole may increase the plasma levels of the vinca alkaloids (e.g. vincristine and vinblastine) and lead to neurotoxicity, which is possibly due to an inhibitory effect on CYP3A4.
Vitamin A:
Based on a case-report in one patient receiving combination therapy with all-trans-retinoid acid (an acid form of vitamin A) and fluconazole, CNS related undesirable effects have developed in the form of psuedotumour cerebri, which disappeared after discontinuation of fluconazole treatment. This combination may be used by the incidence of CNS related undesirable effects should be borne in mind.
Voriconazole (CYP2C9 and CYP3A4 inhibitor):
Co administration of oral voriconazole (400mg Q12h for 1 day, then 200mg Q12h for 2.5 days) and oral fluconazole (400mg on day 1, then 200mg Q24 for 4 days) to 8 healthy male subjects resulted in an increase in Cmax and AUC of voriconazole by an average of 57% (90% CI: 20%, 107%) and 79% (90% CI: 40%, 128%), respectively. The reduced dose and/or frequency of voriconazole and fluconazole that would eliminate this effect have not been established. Monitoring for voriconazole associated adverse events is recommended if voriconazole is used sequentially after fluconazole.
Trimetrexate:
Fluconazole may inhibit the metabolism of trimetrexate, leading to increased trimetrexate plasma concentrations. If the combination cannot be avoided, trimetrexate serum levels and toxicity (bone marrow suppression, renal and hepatic dysfunction, and gastro-intestinal ulceration) must be closely monitored.
Xanthine bases, other antiepileptic drugs and isoniazid:
Follow-up tests must be carried out when fluconazole is administered concomitantly with xanthine bases, other antiepileptic drugs and isoniazide.
Zidovudine:
Two kinetic studies resulted in increased levels of zidovudine most likely caused by the decreased conversion of zidovudine to its major metabolite. One study determined zidovudine levels in AIDS or ARC patients before and following fluconazole 200mg daily for 15 days. There was a significant increase in zidovudine AUC (20%).
A second randomised, two-period, two-treatment crossover study examined zidovudine levels in HIV infected patients.
On two occasions, 21 days apart, patients received zidovudine 200mg every eight hours either with or without fluconazole 400mg daily for seven days. The AUC of zidovudine significantly increased (74%) during coadministration with fluconazole. Patients receiving this combination should be monitored for the development of zidovudine-related adverse reactions.
Azithromycin:
An open-label, randomized, three-way crossover study in 18 healthy subjects assessed the effect of a single 1200 mg oral dose of azithromycin on the pharmacokinetics of a single 800 mg oral dose of fluconazole as well as the effects of fluconazole on the pharmacokinetics of azithromycin. There was no significant pharmacokinetic interaction between fluconazole and azithromycin.
Interaction studies show that concomitant administration of Fluconazole with food intake, cimetidine, antacid, or following total body irradiation in bone marrow transplantation, does not significantly affect Fluconazole absorption.
Physicians should be aware that drug-drug interaction studies with other medications have not been conducted, but that such interactions may occur.