ERYTHROMYCIN - Mar Vista Animal Medical Center

ERYTHROMYCIN

(for veterinary information only)

BRAND NAME: ERY-TAB, ERY-PED, ERYC, GALLIMYCIN and others

AVAILABLE IN
250 mg, 333 mg, 400 mg & 500 mg
TABLETS and
ORAL SUSPENSION

BACKGROUND

Erythromycin is an antibiotic of the macrolide class (the same class as tylosin and azithromycin). It is made naturally from a bacterium called "Streptomyces fradiae" as a protective substance to kill off other bacteria. It acts by interfering with the way other bacteria produce proteins. Because this protein manufacture interference applies only to bacteria and does not interfere with the way mammals make proteins, erythromycin can be used in the treatment of bacterial infections.

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. Antibiotics of this type are called "bacteriostatic" antibiotics. At higher doses, erythromycin can kill bacteria out right which makes it also a "bacteriocidal" antibiotic.

Many bacteria are sensitive to erythromycin and, in the past, erythromycin was a popular choice. Inconveniently, however, erythromycin requires three times daily dosing; now that we have reasonably priced antibiotics for twice or even once daily dosing, the use of erythromycin has tapered. That said, today erythryomycin 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 but its use as a prokinetic agent has opened up a new niche for its service.

Erythromycin is one of the few drugs that is able to penetrate the prostate gland and treat infection there while most other antibiotics are stopped by the "blood-prostate" barrier. This ability to treat prostatitis also presents an opportunity where erythromycin might be selected, though, again dosing three times daily generally makes inconvenient dosing.

Staphylococcus bacteria

Staphylococcus bacteria:
the main target of erythromycin.
(Photo credit: CDC Public Health Image Library)

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. It works best given on an empty stomach.

If a dose is accidentally skipped, do not double up on the next dose. Simply give the dose when it is remembered and time the next dose accordingly.

SIDE EFFECTS

The most common side effects are nausea, diarrhea, and appetite loss. These are generally mild and mitigated by giving the medication with food.

INTERACTIONS WITH OTHER DRUGS

Erythromycin should not be used with other drugs that interfere with bacterial protein production using the same mechanism (50S ribosome binding) or they will compete with each other and interfere with each other. Such other drugs include: clindamycin, lincomycin, chloramphenicol, azithromycin, 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. Other drugs that can increase blood levels of erythromycin include omeprazole (an antacid) and the azole class of antifungal drugs (ketoconazole, itraconazole, and fluconazole.)

Sucralfate, a medicine used for stomach ulcers, can interfere with the absorption of erythromycin. Administration of these medicines should be separated by 2 hours.

When erythromycin and digoxin, a heart medicine, are used concurrently the digoxin blood level will be higher and potentially could be toxic. Other drugs that may also show unexpectedly high blood levels when combined with erythromycin include: bromocriptine (used for female hormone imbalances), buspirone (an anti-anxiety medicine), cyclosporine (an immunomodulator), alprazolam (an anti-panic drug), theophylline (the airway dilator mentioned above), and sildenafil (used for pulmonary hypertension) .

The pro-kinetic effect of erythromycin may be diminished over time as the patient develops tolerance to the drug. This situation can be mitigated and possibly actually avoided by combining erythromycin with metoclopramide, another pro-kinetic drug.

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.

Bioavailability is poor in cats (meaning cats do not absorb the drug from the GI tract well). Erythromycin can be expected to be effective for intestinal infections (i.e. Campylobacter infection) but for an internal infection another antibiotic may be a better choice.

Short version (to help us comply with "Lizzie's Law")

Page last updated: 10/16/2021