Macrolides

Macrolides

Macrolides are used to treat a number of common infections.

They include erythromycin and its derivatives, such as:

§    erythromycin estolate

§    erythromycin ethylsuccinate

§    erythromycin lactobionate

§    erythromycin stearate.

These aren’t derivatives

Other macrolides include:

·                 azithromycin

·                 clarithromycin.

Pharmacokinetics

Because erythromycin is acid-sensitive, it must be buffered or have an enteric coating to prevent destruction by gastric acid. Ery-thromycin is absorbed in the duodenum. It’s distributed to most tissues and body fluids except, in most cases, for cerebrospinal fluid (CSF). However, as a class, macrolides can enter the CSF when meninges are inflamed.

Metabolism and excretion

Erythromycin is metabolized by the liver and excreted in bile in high concentrations; small amounts are excreted in urine. It also crosses the placental barrier and is secreted in breast milk.

Pharmacodynamics

Macrolides inhibit ribonucleic acid (RNA)–dependent protein syn-thesis by acting on a small portion of the ribosome, much like clin-damycin.

Pharmacotherapeutics

Erythromycin has a range of therapeutic uses.

§    It provides a broad spectrum of antimicrobial activity against gram-positive and gram-negative bacteria, including Mycobacteri-um, Treponema, Mycoplasma, and Chlamydia.

§    It’s also effective against pneumococci and group A streptococ-ci. Staphylococcus aureus is sensitive to erythromycin; however, resistant strains may appear during therapy.

§    Erythromycin is the drug of choice for treating Mycoplasmapneumoniae infections as well as pneumonia caused by Legionel-la pneumophila.

An alternative to penicillin

In the patient who’s allergic to penicillin, erythromycin is effective for infections produced by group A beta-hemolytic streptococci or Streptococcus pneumoniae. It may also be used to treat gonor-rhea and syphilis in the patient who can’t tolerate penicillin G or the tetracyclines. Erythromycin may also be used to treat minor staphylococcal infections of the skin.

Ranging far and wide…

Azithromycin provides a broad spectrum of antimicrobial activity against gram-positive and gram-negative bacteria, including My-cobacterium, S. aureus, Haemophilus influenzae, Moraxella ca-tarrhalis, and Chlamydia. It’s also effective against pneumococciand groups C, F, and G streptococci.

§    Clarithromycin is a broad-spectrum antibacterial that’s active against gram-positive aerobes, such as S. aureus, S. pneumoniae, and Streptococcus pyogenes; gram-negative aerobes, such asH. influenzae and M. catarrhalis; and other aerobes such aspneumoniae.

§    Clarithromycin has also been used in combination withantacids, histamine-2 blockers, and proton pump inhibitors to treat Helicobacter pylori–induced duodenal ulcer disease.

Drug interactions

Macrolides may interact with these drugs.

§    Erythromycin, azithromycin, and clarithromycin can increase theophylline levels in the patient receiving high dosages of theo-phylline, increasing the risk of theophylline toxicity.

§    Clarithromycin may increase the concentration of carba-mazepine when used together. (See Adverse reactions tomacrolides.)