THE PET PHARMACY By Wendy C. Brooks, DVM, DipABVP Educational Director, VeterinaryPartner.com

(for veterinary information only)

Brand Name: Ery-tab, Ery-Ped, Eryc, and others

Available in 200 mg, 250 mg, 333 mg & 500 mg tablets and oral suspension

Background

Erythromycin began its story as an antibiotic of the macrolide class (the same class as tylosin and azithromycin). It is made naturally by the bacterium “Streptomyces fradiae” and acts to inhibit bacterial protein synthesis by inhibiting the 50S ribosome, a cellular structure only certain bacteria have and use to make internal protein. Lower doses of erythromycin stop bacteria from reproducing but technically do not kill them. The patient's immune system must be able to finish the job. This type of antibiotic is called a bacteriostatic antibiotic. At higher doses, erythromycin can kill bacteria out right which makes it also a bacteriocidal antibiotic.

One type of bacteria that tend to be sensitive to erythromycin are the Staphylococci, which made erythromycin popular for skin infections (which almost always involve Staph. bacteria). Numerous other bacteria are also sensitive to erythromycin. Sadly, newer drugs came along and erythromycin with its three times daily dosing schedule became prescribed less and less in favor of antibiotics given twice or even once a day.

Today erythromycin has seen some resurgence in popularity. This is partly because of over use of drugs that had previously eclipsed erythromycin. Staphylococci developed resistance to the new drugs leading to a return to older drugs.

Further, a new property of erythromycin was elucidated, one not relating to its antibiotic properties. Erythromycin has what are called "pro-kinetic effects" in the stomach, which means it is able to normalize the rhythmic contractions of a flaccid stomach. This helps relieve nausea and facilitate digestion. Doses used for this purpose are too low to achieve antibiotic activity against bacteria.

Erythromycin is one of the few drugs that is able to penetrate the prostate gland and treat infection there. Most antibiotic are stopped by the "blood-prostate" barrier.

How This Medication Is Used

Erythromycin is used as a stomach pro-kinetic agent as described. It is also used as an antibiotic against infections as described above.  It is also the treatment of choice for intestinal infections caused by Campylobacter bacteria.

Side Effects

The most common side effects are nausea, diarrhea, and appetite loss.

Interactions with other Drugs

Erythromycin should not be used with other drugs that bind the bacterial 50S ribosome or they will compete with each other and interfere with each other. Such other drugs include: clindamycin, lincomycin, chloramphenicol, azithromycin, and tylosin.

Erythromycin is synergized (i.e., works even better) when combined with rifampin or sulfa class antibiotics.

Theophylline, an airway dilator, can reduce clearance of erythromycin from the body thus making toxicity more likely.

When erythromycin and digoxin, a heart medicine, are used concurrently the digoxin blood level will be higher and potentially could be toxic.

Concerns and Cautions

The oral suspension of erythromycin should be stored in the refrigerator; however, after it is dispensed it can be stored at room temperature for up to 14 days.

THIS DRUG IS TOXIC TO GUINEA PIGS, HAMSTERS, RABBITS AND GERBILS!

THIS DRUG IS NOT SAFE FOR USE IN CATTLE OR ADULT HORSES.

This drug is considered able to cause birth defects and should not be used during pregnancy.

The use of erythromycin will falsely elevate the liver enzymes ALT and AST on a blood test. This is not harmful but the veterinarian should be aware of this reaction.

Date Published: 7/9/2006 8:35:00 PM
Date Reviewed/Revised: 06/19/2009