TELITHROMYCIN IS A STRONG INHIBITOR OF THE CYTOCHROME P450 3A4 SYSTEM. CO-ADMINISTRATION OF A DRUG PRIMARILY METABOLIZED BY THE CYTOCHROME P450 3A4 ENZYME SYSTEM LIKE CARBAMAZEPINE, TERFENADINE, CYCLOSPORINE, HEXOBARBITAL, PHENYTOIN MAY RESULT IN INCREASED PLASMA CONCENTRATION & POSSIBLE SIDE EFFECTS. CONTRAINDICATED WITH CISAPRIDE, PIMOZIDE. CONCOMITANT USE OF SIMVASTATIN, LOVASTATIN, OR ATORVASTATIN SHOULD BE AVOIDED SINCE IT INCREASES THEIR PLASMA LEVEL DUE TO INHIBITION OF THEIR METABOLISM & HIGH LEVELS OF HMG-COA REDUCTASE INHIBITORS INCREASE THE RISK OF MYOPATHY.
CONCOMITANT USE OF TELITHROMYCIN WITH A CYP 3A4 INDUCER SUCH AS RIFAMPICIN, PHENYTOIN, CARBAMAZEPINE, OR PHENOBARBITAL IS LIKELY TO RESULT IN SUBTHERAPEUTIC LEVELS OF TELITHROMYCIN AND LOSS OF EFFECT.
PLASMA LEVELS OF DIGOXIN, MIDAZOLAM & OTHER BENZODIAZEPINES SHOULD BE MONITORED DURING CO-ADMINISTRATION. TELITHROMYCIN MAY POTENTIATE THE EFFECTS OF THE ORAL ANTICOAGULANTS. METOPROLOL, A CYP 2D6 SUBSTRATE, MAY HAVE INCREASED PLASMA LEVELS ON CO-SDMINISTRATION. DRUGS METABOLIZED BY THE CYTOCHROME P450 SYSTEM SUCH AS CARBAMAZEPINE, CYCLOSPORINE, TACROLIMUS, SIROLIMUS, HEXOBARBITAL, AND PHENYTOIN MAY HAVE ELEVATED SERUM LEVELS ON CO-ADMINISTERED WITH TELITHROMYCIN. ERGOT ALKALOID DERIVATIVES SUCH AS ERGOTAMINE OR DIHYDROERGOTAMINE MAY CAUSE ACUTE ERGOT TOXICITY CHARACTERIZED BY SEVERE PERIPHERAL VASOSPASM AND DYSESTHESIA WHEN CO-ADMINISTERED. IT SHOULD BE AVOIDED IN COMBINATION WITH ANTIARRHYTHMIC DRUGS LIKE QUINIDINE, PROCAINAMIDE, DOFETILIDE ETC.