Roxithromycin Warfarin

Roxithromycin did not alter the pharmacokinetics of carbamazepine (15) or interact with warfarin, ranitidine, or antacids containing hydroxides of aluminium and magnesium (1). 

Clinically important, potentially hazardous interactions with atorvastatin, bexarotene, cyclosporine, dicumarol, ezetimibe, fluvastatin, interferon alfa, lovastatin, nicotinic acid, pioglitazone, pravastatin, repaglinide, rosuvastatin, roxithromycin, simvastatin, statins, warfarin... 

Clinically important, potentially hazardous interactions with amiodarone, atazanavir, azithromycin, bosentan, ciprofibrate, clarithromycin, clopidogrel, cyclosporine, darunavir, delavirdine, diltiazem, erythromycin, fosamprenavir, fusidic acid, gemfibrozil, grapefruit juice, imatinib, itraconazole, lopinavir, rabeprazole, ranolazine, red rice yeast, ritonavir, roxithromycin, selenium, St John s wort, tacrolimus, telithromycin, tipranavir, verapamil, warfarin... 

Roxithromycin did not alter the pharmacokinetics or effect of warfarin in one study. However, there are at least 2 published cases of interactions with coumarins, and one report reviewing 16 cases. These are diseussed below. 

Erythromycin is a known inhibitor of the cytochrome P450 isoenzyme CYP3A4. However, this isoenzyme has only a minor role in the metabolism of warfarin , (p.358), specifically the less active R-isomer of warfarin. Consequently, only minor increases in the levels of warfarin have been seen in pharmacokinetic studies, which would generally not be expected to be clinically relevant. However, it is possible that even these small changes might be important in a very few patients, particularly those with a low prothrombin complex aetivity. Other macrolides (azithromycin, clarithromycin, dirithromycin, roxithromycin) have less effect on CYP3A4 than erythromycin, and consequently would be expected to have even less effect on the pharmacokinetics of warfarin or acenocoumarol, which is borne out in the few studies available. Nevertheless, cases of interactions have been reported for nearly all these macrolides. Moreover, one cohort study found that clarithromycin increased the risk of an interaction and erythromycin did not. It is possible that there is some other, as yet unidentified, mechanism involved. Alternatively, it is equally possible that the relatively few cases just represent idiosyncratic effects attributable to other factors, and not to any interaction (see also Coumarins -i- Antibacterials , p.365). 

Paulsen O, Nilssai L-G, Saint-Salvi B, Manuel C, Lunell E. No effect of roxithromycin on pharmacokinetic or i 4iarmacodynamic properties of warfarin and its enantiomers. Pharmacol Taxicol( 9ZZ) 63,215-20. 

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