Erythromycin is a macrolide antibiotic which has an antimicrobial spectrum similar or slightly wider to that of penicillin, and is often used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including mycoplasma. It is also used to treat outbreaks of chlamydia, syphilis, and gonorrhea.

Erythromycin is produced from a strain of the actinomyces Saccaropolyspora erythraea , formerly known as Streptomyces erythraeus.

Erythromycin A
(3R*, 4S*, 5S*, 6R*, 7R*, 9R*, 11R*, 12R*, 13S*, 14R*)-4-((2,6-Dideoxy-3-C-methyl-3-O-methyl-a-L- ribo- hexopyranosyl) -oxy) -14- ethyl-7,12,13- trihydroxy - 3,5,7,9,11,13-hexa methyl-6- ((3,4,6-trideoxy-3-(dimethylamino)-b-D-xylo- hexopyranosyl)oxy)oxacyclotetradecane-2,10-dione
Molecular Weight	733.93
Empiric Formula	C37H67NO13
ATC code	J01FA01
Metabolism	Liver
Pregnancy category	B (USA) A (Aus)

History

Abelardo Aguilar , a Filipino scientist, sent some soil samples to his employer Eli Lilly in 1949. Eli Lilly’s research team, led by J. M. McGuire, managed to isolate erythromycinin from the metabolic products of a strain of Streptocyces erythreus found in the samples. The product was subsequently launched in 1952 under the brand name Ilosone (after the Philippine region of Iloilo where it was originally collected from). Erythromycin was formerly also called ilotycin.

Available forms

Erythromycin is available in enteric-coated tablets, oral suspensions, ointments, gels and injections.

Mechanism of action

Erythromycin prevents bacteria from growing, by interfering with their protein synthesis. Erythromycin binds to the subunit 50S of the bacterial ribosome, and thus inhibits the translocation of peptides.

Pharmacokinetics

Erythromycin is easily inactivated by gastric acids, therefore all orally administered formulations are given as either enteric coated or as more stable salts or esters. Erythromycin is very rapidly absorbed, and diffused into most tissues and phagocytes. Due to the high concentration in phagocytes, erythromycin is actively transported to the site of infection, where during active phagocytosis, large concentrations of erythromycin are released.

Metabolism

Most of erythromycin is metabolised by demethylation in the liver. Its main route elimination route is in the bile, and a small portion in the urine. Erythromycin's half-life is 1.5 hours.

Side-effects

Gastrointestinal intestinal disturbances such as diarrhoea, nausea, abdominal pain and vomiting are fairly common so it tends not to be prescribed as a first-line drug. More serious side-effects, such as reversible deafness are rare. Cholestatic jaundice, Stevens-Johnson syndrome and toxic epidermal necrosis are some other rare side effects that may occur.

Contraindications

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 (Ray et al 2004). Hence, erythromycin should not be administered in patients using these drugs, or drugs that also prolong the QT time. Other examples include terfenadine (Seldane, Seldane-D), astemizole (Hismanal), cisapride (Propulsid, withdrawn in many countries for prolonging the QT time) and pimozide (Orap).

References

• Ray WA, Murray KT, Meredith S, Narasimhulu SS, Hall K, Stein CM. Oral Erythromycin and the Risk of Sudden Death from Cardiac Causes. N Engl J Med 2004;351:1089-96.
• British National Formulary "BNF 49" March 2005.