| Interaction studies have only been performed in adults.• Effect of Ketek on other medicinal productsTelithromycin is an inhibitor of CYP3A4 and a weak inhibitor of CYP2D6. In vivo studies with simvastatin, midazolam and cisapride have demonstrated a potent inhibition of intestinal CYP3A4 and a moderate inhibition of hepatic CYP3A4. The degree of inhibition with different CYP3A4 substrates is difficult to predict. Hence, Ketek should not be used during treatment with medicinal products that are CYP3A4 substrates, unless plasma concentrations of the CYP3A4 substrate, efficacy or adverse reactions can be closely monitored. Alternatively, interruption in the treatment with the CYP3A4 substrate should be made during treatment with Ketek. Cyclosporin, tacrolimus, sirolimus Due to its CYP3A4 inhibitory potential, telithromycin can increase blood concentrations of these CYP34A4 substrates. Thus, when initiating telithromycin in patients already receiving any of theses immunosuppressive agents, cyclosporin, tacrolimus or sirolimus levels must be carefully monitored and their doses decreased as necessary. When telithromycin is discontinued, cyclosporin, tacrolimus or sirolimus levels must be again carefully monitored and their dose increased as necessary.Metoprolol When metoprolol (a CYP2D6 substrate) was coadministered with Ketek, metropolol Cmax and AUC were increased by approximately 38%, however, there was no effect on the elimination half-life of metoprolol. The increase exposure to metoprolol may be of clinical importance in patients with heart failure treated with metoprolol. In these patients, co-administration of Ketek and metoprolol, a CYP2D6 substrate, should be considered with caution.Medicinal products with a potential to prolong QT interval Ketek is expected to increase the plasma levels of cisapride, pimozide, astemizole and terfenadine. This could result in QT interval prolongation and cardiac arrhythmias including ventricular tachycardia, ventricular fibrillation and torsades de pointes. Concomitant administration of Ketek and any of these medicinal products is contraindicated (see section 4.3).Caution is warranted when Ketek is administered to patients taking other medicinal products with the potential to prolong QT interval (see section 4.4).Ergot alkaloid derivatives (such as ergotamine and dihydroergotamine) By extrapolation from erythromycin A and josamycin, concomitant medication of Ketek and alkaloid derivatives could lead to severe vasoconstriction (ergotism) with possibly necrosis of the extremities. The combination is contraindicated (see section 4.3).Statins When simvastatin was coadministered with Ketek, there was a 5.3 fold increase in simvastatin Cmax, an 8.9 fold increase in simvastatin AUC, a 15-fold increase in simvastatin acid Cmax and an 11-fold increase in simvastatin acid AUC. Ketek may produce a similar interaction with lovastatin and atorvastatin which are also mainly metabolised by CYP3A4. Ketek should therefore not be used concomitantly with simvastatin, atorvastatin, or lovastatin (see section 4.3). Treatment with these agents should be interrupted during Ketek treatment. The exposure of pravastatin, rosuvastatin and to a lesser extent fluvastatin, may be increased due to possible involvement of transporters proteins, but this increase is expected to be lesser than interactions involving CYP3A4 inhibition. However, patients should be carefully monitored for signs and symptoms of myopathy and rhabdomyolysis when co-treated with pravastatin, rosuvastatin and fluvastatin.Benzodiazepines When midazolam was coadministered with Ketek, midazolam AUC was increased 2.2-fold after intravenous administration of midazolam and 6.1-fold after oral administration. The midazolam half-life was increased about 2.5-fold. Oral administration of midazolam concomitantly with Ketek should be avoided. Intravenous dosage of midazolam should be adjusted as necessary and monitoring of the patient should be undertaken. The same precautions should also apply to the other benzodiazepines which are metabolised by CYP3A4, (especially triazolam but also to a lesser extent alprazolam). For those benzodiazepines which are not metabolised by CYP3A4 (temazepam, nitrazepam, lorazepam) an interaction with Ketek is unlikely.Digoxin Ketek has been shown to increase the plasma concentrations of digoxin. The plasma trough levels, Cmax, AUC and renal clearance were increased by 20%, 73%, 37% and 27% respectively, in healthy volunteers. There were no significant changes in ECG parameters and no signs of digoxin toxicity were observed. Nevertheless, monitoring of serum digoxin level should be considered during concomitant administration of digoxin and Ketek.Theophylline There is no clinically relevant pharmacokinetic interaction of Ketek and theophylline administered as extended release formulation. However, the co-administration of both medicinal products should be separated by one hour in order to avoid possible digestive side effects such as nausea and vomiting.Oral anticoagulants Increased anticoagulant activity has been reported in patients simultaneously treated with anticoagulants and antibiotics, including telithromycin. The mechanisms are incompletely known. Although Ketek has no clinically relevant pharmacokinetic or pharmacodynamic interaction with warfarin after single dose administration, more frequent monitoring of prothrombin time/INR (International Normalised Ratio) values should be considered during concomitant treatment.Oral contraceptives There is no pharmacodynamic or clinically relevant pharmacokinetic interaction with low-dose triphasic oral contraceptives in healthy subjects.• Effect of other medicinal products on KetekDuring concomitant administration of rifampicin and telithromycin in repeated doses, Cmax and AUC of telithromycin were on average decreased by 79% and 86% respectively. Therefore, concomitant administration of CYP3A4 inducers (such as rifampicin, phenytoin, carbamazepine, phenobarbital, St John's wort) is likely to result in subtherapeutic levels of telithromycin and loss of effect. The induction gradually decreases during 2 weeks after cessation of treatment with CYP3A4 inducers. Ketek should not be used during and 2 weeks after treatment with CYP3A4 inducers.Interaction studies with itraconazole and ketoconazole, two CYP3A4 inhibitors, showed that maximum plasma concentrations of telithromycin were increased respectively by 1.22 and 1.51 fold and AUC by respectively 1.54 fold and 2.0 fold. These changes in the pharmacokinetics of telithromycin do not necessitate dosage adjustment as telithromycin exposure remains within a well tolerated range. The effect of ritonavir on telithromycin has not been studied and could lead to larger increase in telithromycin exposure. The combination should be used with caution.Strong CYP3A4 inhibitors must not be co-administered with Ketek in patients with severe renal/or hepatic dysfunction (see section 4.3).Ranitidine (taken 1 hour before Ketek) and antacid containing aluminium and magnesium hydroxide has no clinically relevant influence on telithromycin pharmacokinetics. | |