(for veterinary information only)
200 mg, 250 mg, 333 mg & 500 mg
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 a cellular structure only certain bacteria have/use to make internal proteins. This structure is called the "50S ribosome." This process works well because non-bacterial cells use a different type of ribosome called a "60S ribosome."
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.
One type of bacteria that tend to be sensitive to erythromycin are the Staphylococci. This has made erythromycin popular for skin infections (which almost always involve Staph. bacteria). Numerous other bacteria are also sensitive to erythromycin; however, newer drugs have come along leaving erythomycin with its three times daily dosing schedule to be prescribed less and less in favor of antibiotics given twice or even once a day.
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.
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.
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.
The most common side effects are nausea, diarrhea, and appetite loss.
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, 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.
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.
Page last updated: 10/10/2013