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Related to Erythromycins: Erythrocin




Erythromycins are medicines that kill bacteria or prevent their growth.


Erythromycins are antibiotics, medicines used to treat infections caused by microorganisms. Physicians prescribe these drugs for many types of infections caused by bacteria, including strep throat, sinus infections, pneumonia, ear infections, tonsillitis, bronchitis, gonorrhea, pelvic inflammatory disease (PID), and urinary tract infections. Some medicines in this group are also used to treat Legionnaires' disease and ulcers caused by bacteria. These drugs will not work for colds, flu, and other infections caused by viruses.


The drugs described here include erythromycins (Erythrocin, Ery-C, E-Mycin, and other brands) and medicines that are chemically related to erythromycins, such as azithromycin (Zithromax) and clarithromycin (Biaxin). They are available only with a physician's prescription and are sold in capsule, tablet (regular and chewable), liquid, and injectable forms.

Recommended dosage

The recommended dosage depends on the type of erythromycin, the strength of the medicine, and the medical problem for which it is being taken. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage.
Always take erythromycins exactly as directed. Never take larger, smaller, more frequent, or less frequent doses. To make sure the infection clears up completely, it is very important to take the medicine for as long as it has been prescribed. Do not stop taking the drug just because symptoms begin to improve. This is important with all types of infections, but it is especially important in "strep" infections, which can lead to serious heart problems if they are not cleared up completely.
Erythromycins work best when they are at constant levels in the blood. To help keep levels constant, take the medicine in doses spaced evenly through the day and night. Do not miss any doses. Some of these medicines are most effective when taken with a full glass of water on an empty stomach, but they may be taken with food if stomach upset is a problem. Others work equally well when taken with or without food. Check package directions or ask the physician or pharmacist for instructions on how to take the medicine.


Symptoms should begin to improve within a few days of beginning to take this medicine. If they do not, or if they get worse, check with the physician who prescribed the medicine.
Erythromycins may cause mild diarrhea, that usually goes away during treatment. However, severe diarrhea could be a sign of a very serious side effect. Anyone who develops severe diarrhea while taking erythromycin or related drugs should stop taking the medicine and call a physician immediately.

Special conditions

Taking erythromycins may cause problems for people with certain medical conditions or people who are taking certain other medicines. Before taking these drugs, be sure to let the physician know about any of these conditions:
ALLERGIES. Anyone who has had unusual reactions to erythromycins, azithromycin, or clarithromycin in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.
PREGNANCY. Some medicines in this group may cause problems in pregnant women and have the potential to cause birth defects. Women who are pregnant or who may become pregnant should check with their physicians before taking these drugs.
BREASTFEEDING. Erythromycins pass into breast milk. Mothers who are breastfeeding and who need to take this medicine should check with their physicians.
OTHER MEDICAL CONDITIONS. Before using erythromycins, people with any of these medical problems should make sure their physicians are aware of their conditions:
  • heart disease
  • liver disease
  • hearing loss
USE OF CERTAIN MEDICINES. Taking erythromycins with certain other drugs may affect the way the drugs work or may increase the chance of side effects.

Side effects

The most common side effects are mild diarrhea, nausea, vomiting, and stomach or abdominal cramps. These problems usually go away as the body adjusts to the drug and do not require medical treatment. Less common side effects, such as sore mouth or tongue and vaginal itching and discharge also may occur and do not need medical attention unless they persist or are bothersome.
More serious side effects are not common, but may occur. If any of the following side effects occur, check with a physician immediately:
  • severe stomach pain, nausea, vomiting, or diarrhea
  • fever
  • skin rash, redness, or itching
  • unusual tiredness or weakness
Although rare, very serious reactions to azithromycin (Zithromax) are possible, including extreme swelling of the lips, face, and neck, and anaphylaxis (a violent allergic reaction). Anyone who develops these symptoms after taking azithromycin should stop taking the medicine and get immediate medical help.
Other rare side effects may occur with erythromycins and related drugs. Anyone who has unusual symptoms after taking these medicines should get in touch with his or her physician.


Erythromycins may interact with many other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes erythromycins should let the physician know all other medicines he or she is taking. Among the drugs that may interact with erythromycins are:
  • acetaminophen (Tylenol)
  • medicine for overactive thyroid
  • male hormones (androgens)
  • female hormones (estrogens)
  • other antibiotics
  • blood thinners
  • disulfiram (Antabuse), used to treat alcohol abuse
  • antiseizure medicines such as valproic acid (Depakote, Depakene)
  • caffeine
  • the antihistamines astemizole (Hismanal)
  • antiviral drugs such as (zidovudine) Retrovir

Key terms

Bronchitis — Inflammation of the air passages of the lungs.
Gonorrhea — A sexually transmitted disease (STD) that causes infection in the genital organs and may cause disease in other parts of the body.
Inflammation — Pain, redness, swelling, and heat that usually develop in response to injury or illness.
Legionnaire's disease — A lung disease caused by a bacterium.
Microorganism — An organism that is too small to be seen with the naked eye.
Pelvic inflammatory disease (PID) — Inflammation of the female reproductive tract, caused by any of several microorganisms. Symptoms include severe abdominal pain, high fever, and vaginal discharge. Severe cases can result in sterility.
Pneumonia — A disease in which the lungs become inflamed. Pneumonia may be caused by bacteria, viruses, or other organisms, or by physical or chemical irritants.
Sinus — Any of several air-filled cavities in the bones of the skull.
Strep throat — A sore throat caused by infection with Streptococcus bacteria. Symptoms include sore throat, chills, fever, and swollen lymph nodes in the neck.
Tonsillitis — Inflammation of a tonsil, a small mass of tissue in the throat.
Urinary tract — The passage through which urine flows from the kidneys out of the body.
The list above does not include every drug that may interact with erythromycins. Be sure to check with a physician or pharmacist before combining erythromycins with any other prescription or nonprescription (over-the-counter) medicine.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.