Carbamazepine: administration of carbamazepine with clarithromycin has been shown to increase significantly the plasma concentration of carbamazepine; carbamazepine serum levels should be monitored.
Digoxin: concurrent administration of digoxin with clarithromycin has been shown to increase serum digoxin concentrations; monitoring of digoxin serum levels is recommended.
Rifabutin or Rifampin: concurrent use of clarithromycin and rifabutin or rifampin decreases the serum concentration of clarithromycin by >50 %.
Terfenadine: concurrent use of clarithromycin and terfenadine may increase the plasma concentration of terfenadine and its active metabolite by 2 to 3 times; concurrent use should be avoided.
Theophylline: concurrent administration with clarithromycin has been shown to increase the AUC of theophylline by 17%; monitoring of theophylline serum levels is recommended.
Warfarin: concurrent administration with clarithromycin has been shown to potentiate the effects of warfarin; prothrombin time should be closely monitored.
Ergotamine or dihydroergotamine: concurrent use with clarithromycin has been associated in some patients with acute ergot toxicity.
Triazolam: There have been reports of CNS effects with the concomitant use of clarithromycin and triazolam.
Cyclosporine, tacrolimus, hexobarbital, phenytoin, alfentanil, Quinidine/disopyramide, lovastatin, bromocriptine, valproate, astemizole and other drugs metabolised by the cytochrome P450 system: concurrent use with clarithromycin may be associated with elevations in serum levels of these other drugs; serum concentrations should be closely monitored.
Drug metabolised by CYP3A isoenzyme: Clarithromycin has the potential to interact with the large number of drugs through its action on hepatic cytochrome P450 isoenzymes, particularly CYP1A2 and CYP3A4. Macrolides inhibit drug metabolism by microsomal cytochromes by competitive inhibition and by the formation of inactive complexes. Such interactions can result in severe adverse effects, including ventricular arrhythmias with the non-sedative antihistamines astemizole and terfenadine and with the prokinetic drug cisapride. Clarithromycin is less likely to inhibit the hepatic metabolism of other drugs, although those undergoing first-pass metabolism may still be affected.
Zidovudine: Simultaneous oral administration of zidovudine and clarithromycin resulted in a lower peak serum concentration [Cmax], lower AUC, and delayed time to peak concentration [Tmax] of zidovudine should be taken at least hours apart.
Maalox and Ranitidine: lncreased plasma concentrations of clarithromycin may also occur when it is co-administered with Maalox or ranitidine. No adjustment to the dosage is necessary.
Omeprazole: In a study in healthy subjects, increased concentrations of clarithromycin and its active metabolite were observed in gastric tissue and mucus and to lesser external in plasma during concomitant administration of omeprazole. In addition, administration of clarithromycin with omeprazole resulted in higher and more prolonged plasma concentrations of omeprazole.