Mastour S Al Ghamdi, Suman Jain.
Clinically reported drug interactions with Erythromycin - An update.
Pak J Med Res Jan ;41(4):162-72.

Background: Erythromycin, the prototypical macrolide, has been widely used since 1950s in the management of infections. It is often combined with other drug therapies, thus creating a potential for pharmacokinetic interactions. It can both inhibit drug metabolism in the liver by complex formation and inactivation of microsomal drug oxidizing enzymes, and also by interfering with microorganisms of the enteric flora through its antibiotic effects. Methodology: Using MEDLINE search (1975-April 2002) all available clinical studies, review articles, and case reports were reviewed to provide an unbiased account of drug interactions with erythromycin. A number of reports and controlled studies have incriminated erythromycin as a potential source of clinically severe drug interactions. For example torsades de pointes associated with QT prolongation occurred with terfenadine, astemizole, and cisapride. Cases of rhabdomyolysis have been reported on concomitant use of statins. Symptomatic hypotension occurred with calcium channel blockers or sildenafil. Excessive sedation occurred from concurrent use of benzodiazepines, buspirone and zopiclone. Ataxia occurred with carbamazepine and valproate, and ergotism with ergotamine. Serotonin syndrome was reported with the use of sertraline and psychosis with bromocriptine. Interactions with cyclosporine, tacrolimus, theophylline, and warfarin are also clinically important. These interactions are due to decreased clearance of these drugs. Increase in digoxin concentration was mainly due to increase in bioavailability. Erythromycin should, therefore, be not administered with some of these drugs or their dosage schedule readjusted. Conclusions: In most cases, the extent of drug interaction varies widely among individuals; this is likely dependent on interindividual differences in CYP3A4 tissue content, preexisting medical conditions and possibly, age. Interactions may occur under single dose conditions or only at steady state. The pharmacodynamic consequences may or may not closely follow pharmacokinetic changes. Drug interactions may be most important when patients are stabilized on the affected drug and erythromycin is then administered.

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