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

Available in 250 mg, 333 mg, 400 mg & 500 mg tablets and oral suspension (liquid)

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 interference applies only to bacteria and not with the way mammals make proteins, erythromycin can be used to treat bacterial infections.

Furthermore, a new property of erythromycin was revealed that does not relate to bacteria. Erythromycin has what are called prokinetic effects in the stomach, which means it can normalize the rhythmic contractions of a flaccid stomach. This normalization helps relieve nausea and aid digestion. The doses for normalization are too low to achieve antibiotic activity against bacteria, but its use to stimulate movement has opened up a new niche for its service.

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 outright, which also makes it 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 the overuse 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 is also an opportunity where erythromycin might be selected, though, again, dosing three times daily generally makes inconvenient dosing.

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 giving it with food will help get rid of those side effects.

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 and interfere with each other. Such other drugs include clindamycin, lincomycin, chloramphenicol, azithromycin, and tylosin.

Erythromycin 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 omeprazone (an antacid) and the azole class of antifungal drugs (ketoconazole, itraconazole, and fluconazole).

Sucralfate, a medicine used for stomach ulcers, can interfere with absorption of erythromycin. These medicines should be given 2 hours apart.

When erythromycin and the heart medicine digoxin 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 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 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 well from the GI tract). 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.