indication

For the treatment of the following mild-to-moderate infections caused by susceptible strains of microorganisms: acute bacterial exacerbations of chronic bronchitis, secondary bacterial infection of acute bronchitis, community-acquired pneumonia, pharyngitis/tonsilitis, and uncomplicated skin and skin structure infections.

pharmacology

Dirithromycin is a pro-drug which is converted non-enzymatically during intestinal absorption into the microbiologically active moiety erythromycylamine. Erythromycylamine exerts its activity by binding to the 50S ribosomal subunits of susceptible mircoorganisms resulting in inhibition of protein synthesis. Dirithromycin/erythromycylamine has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections: Staphylococcus aureus (methicillin-susceptible strains only), Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, Legionella pneumophila, Moraxella catarrhalis, and Mycoplasma pneumoniae.

mechanism of action

Dirithromycin prevents bacteria from growing, by interfering with their protein synthesis. Dirithromycin binds to the 50S subunit of the 70S bacterial ribosome, and thus inhibits the translocation of peptides. Dirithromycin has over 10 times higher affinity to the subunit 50S than erythromycin. In addition, dirithromycin binds simultaneously in to two domains of 23S RNA of the ribosomal subunit 50S, where older macrolides bind only in one. Dirithromycin can also inhibit the formation of ribosomal subunits 50S and 30S.

toxicity

The toxic symptoms following an overdose of a macrolide antibiotic may include nausea, vomiting, epigastric distress, and diarrhea.

biotransformation

Dirithromycin is converted by nonenzymatic hydrolysis during absorption to the active compound, erythromycylamine. Sixty to 90% of a dose is hydrolyzed to erythromycylamine within 35 minutes after dosing, and conversion is nearly complete after 1.5 hours. Erythromycylamine undergoes little or no hepatic biotransformation. No other metabolites of dirithromycin have been detected in the serum.

absorption

Oral dirithromycin is rapidly absorbed, with an absolute bioavailability of approximately 10%. Dietary fat has little or no effect on the bioavailability of dirithromycin.

half life

The mean plasma half-life of erythromycylamine was estimated to be about 8 h (2 to 36 h), with a mean urinary terminal elimination half-life of about 44 h (16 to 65 h) in patients with normal renal function.

drug interactions

Ranolazine: Increased levels of ranolazine - risk of toxicity

Vinblastine: Dirithromycin, a CYP3A4 and p-glycoprotein inhibitor, may increase the Vinblastine serum concentration and distribution in certain cells. Consider alternate therapy to avoid Vinblastine toxicity. Monitor for changes in the therapeutic/adverse effects of Vinblastine if Dirithromycin is initiated, discontinued or dose changed.

Vincristine: Dirithromycin, a CYP3A4 and p-glycoprotein inhibitor, may increase the Vincristine serum concentration and distribution in certain cells. Consider alternate therapy to avoid Vincristine toxicity. Monitor for changes in the therapeutic and adverse effects of Vincristine if Dirithromycin is initiated, discontinued or dose changed.

Vinorelbine: Dirithromycin, a CYP3A4 and p-glycoprotein inhibitor, may increase the Vinorelbine serum concentration and distribution in certain cells. Consider alternate therapy to avoid Vinorelbine toxicity. Monitor for changes in the therapeutic and adverse effects of Vinorelbine if Dirithromycin is initiated, discontinued or dose changed.