Zenith Suspension Drug Interactions

Theophylline: Pharmacokinetic studies in healthy volunteers revealed no interaction between azithromycin and theophylline with concomitant administration. Since interactions of other macrolides with theophylline were reported, care should be taken of signs of increased theophylline levels.
Coumarin-type oral anticoagulants: An increased tendency of hemorrhage has been reported in connection with the concurrent use of Azithromycin monohydrate (Zenith) and warfarin or coumarin-like oral anticoagulants. Attention should be paid to the frequency of prothrombin time monitoring.
Carbamazepine: In a pharmacokinetic interaction study in healthy volunteers, no significant effect was seen in the pharmacokinetics of carbamazepine or its active metabolite.
Ergotamine derivatives: In patients treated with ergotamine derivatives, ergotism can be induced by the concomitant administration of some macrolide antibiotics. There is no known data about the possibility of an interaction between ergotamine derivatives and Azithromycin monohydrate (Zenith). Because of the theoretical possibility of ergotism, Azithromycin monohydrate (Zenith) and ergotamine derivatives should not be combined.
Cyclosporine: Since pharmacokinetic and clinical studies on the possible combined effects of Azithromycin monohydrate (Zenith) and cyclosporine have not been carried out, the therapeutic situation should be carefully considered before these active substances are administered simultaneously. If combination treatment is considered justifiable, the cyclosporine levels should be carefully monitored and the dosage should be adjusted accordingly.
Digoxin: It is known that some macrolide antibiotics limit the metabolism of digoxin (in the gut). In patients treated concomitantly with Azithromycin monohydrate (Zenith) and digoxin, the possibility of increased digoxin levels should be borne in mind, and digoxin levels monitored.
Antacids: In a pharmacokinetic study on the effect of concomitant administration of antacids and Azithromycin monohydrate (Zenith), no effect on the total bioavailability was seen, although the peak serum levels were reduced by 30%. Azithromycin monohydrate (Zenith) should be taken at least 1 hours before or 2 hours after the antacid.
Trimethoprim/Sulfamethoxazole: Coadministration of trimethoprim/sulfamethoxazole (160 mg/800 mg) for 7 days with Azithromycin monohydrate (Zenith) 1200 mg on day 7 had no significant effect on peak concentrations, total exposure or urinary excretion of either trimethoprim or sulfamethoxazole. Azithromycin monohydrate (Zenith) serum concentrations were similar to those seen in other studies.
Fluconazole: Coadministration of a single dose of 1200 mg Azithromycin monohydrate (Zenith) did not alter the pharmacokinetics of a single dose of 800 mg fluconazole. Total exposure and t_½ of azithromycin monohydrate were unchanged by the co-administration of fluconazole, however, a clinically insignificant decrease in C_max (18%) of azithromycin monohydrate was observed.
Zidovudine: Single administrations of 1000 mg of Azithromycin monohydrate (Zenith) and multiple administrations of 600 or 1200 mg Azithromycin monohydrate (Zenith) had no effect on the plasma pharmacokinetics or the renal excretion of zidovudine or its glucuronide metabolite. However, administration of Azithromycin monohydrate (Zenith) increased the concentrations of phosphorylated zidovudine, the clinically active metabolite, in peripheral blood mononuclear cells. The clinical significance of this finding is unclear, but it may be of benefit to patients.
Terfenadine: Azithromycin monohydrate (Zenith) has no effect on the pharmacokinetics of terfenadine administered every 12 hours in the recommended dosage of 60 mg. Measured in a steady-state dosing of terfenadine, adding Azithromycin monohydrate (Zenith) did not result in a significant change in the cardiac repolarization (QT interval).
Cisapride: Cisapride is metabolized in the liver by the enzyme CYP3A4. Because macrolides inhibit this enzyme, concomitant administration of cisapride may cause the increase of QT interval prolongation, ventricular arrhythmias and Torsades de pointes.
Didanosine: In comparison to placebo, daily doses of 1200 mg azithromycin monohydrate and didanosine did not seem to have an effect on the pharmacokinetics of didanosine in the 6 test subjects.
Rifabutin: Coadministration of Azithromycin monohydrate (Zenith) and rifabutin did not affect the serum concentrations of either active substance. Neutropenia was observed in subjects receiving concomitant treatment of Azithromycin monohydrate (Zenith) and rifabutin.
Although neutropenia has been associated with the use of rifabutin, a causal relationship to combination with Azithromycin monohydrate (Zenith) has not been established.
Astemizole, Triazolam, Midazolam, Alfentanil: There is no known data regarding interaction with astemizole, triazolam, midazolam or alfentanil. Caution is needed in the concomitant use of these medicinal products and Azithromycin monohydrate (Zenith), as an increase of action with the concomitant use of the macrolide antibiotic erythromycin has been described.
Indinavir: Coadministration of a single dose of 1200 mg Azithromycin monohydrate (Zenith) had no statistically significant effect on the pharmacokinetics of indinavir administered as 800 mg 3 times daily for 5 days.
Nelfinavir: Concomitant administration of 1200 mg Azithromycin monohydrate (Zenith) and steady-state nelfinavir (750 mg 3 times daily) resulted in an average 16% decrease of nelfinavir AUC, an increase of Azithromycin monohydrate (Zenith) AUC and C_max with 113% and 136%, respectively. No dose adjustment is necessary but patients should be monitored for known side effects of Azithromycin monohydrate (Zenith).