Interactions
Erythromycin is metabolized by enzymes of the cytochrome P450 system, in particular, by isozymes of the CYP3A superfamily, CYP3A (Hunt et al., 1992). The activity of the CYP3A enzymes can be induced or inhibited by certain drugs (e.g. dexamethasone) which can cause it to affect the metabolism of many different drugs, e.g. erythromycin. If other CYP3A substrates — drugs that are broken down by CYP3A - such as simvastatin (Zocor), lovastatin (Mevacor), or atorvastatin (Lipitor)—are taken concomitantly with erythromycin, levels of the substrates will increase, often causing adverse effects. A noted drug interaction involves erythromycin and simvastatin, resulting in increased simvastatin levels and the potential for rhabdomyolysis. Another group of CYP3A4 substrates are drugs used for migraine such as ergotamine and dihydroergotamine; their adverse effects may be more pronounced if erythromycin is associated. Earlier case reports on sudden death prompted a study on a large cohort that confirmed a link between erythromycin, ventricular tachycardia, and sudden cardiac death in patients also taking drugs that prolong the metabolism of erythromycin (like verapamil or diltiazem) by interfering with CYP3A4. Hence, erythromycin should not be administered to people using these drugs, or drugs that also prolong the QT interval. Other examples include terfenadine (Seldane, Seldane-D), astemizole (Hismanal), cisapride (Propulsid, withdrawn in many countries for prolonging the QT time) and pimozide (Orap). Theophylline, which is used mostly in asthma, is also contraindicated.
Erythromycin is not recommended when using clindamycin-containing products, even topical products such as Duac or BenzaClin. In general, the simultaneous use of two different erythromycin derivatives (such as clindamycin and Mitemcinal) should be avoided as drugs in this macrolide family possess a common mechanism of action.
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