Erythromycins, also called macrolides, are a group of antibiotics , medicines that kill bacteria or prevent their growth.


The antibiotics in this group are:

  • azithromycin (Zithromax)
  • clarithromycin (Biaxin)
  • clindamycin (Cleocin)
  • erythromycin (EES, Pediazole)
  • lincomycin (Lincocin)

These drugs are chemically related and have similar uses, but because they are distributed differently in the body, they may be used for different purposes. There are other, older drugs in this group, but they are no longer in general use.

General use

Erythromycin is similar in use to penicillin and is widely used for patients who are allergic to penicillin. Penicillin has advantages over erythromycin in that it kills bacteria, while erythromycin only stops bacterial growth and relies on the body's immune system to kill bacteria. Also, erythromycin is more likely to cause stomach upset than is penicillin. Sometimes erythromycin may be used to treat a microorganism that is resistant to penicillin.

Azithromycin and clarithromycin both reach the lungs and respiratory tract better than does erythromycin. These two drugs may be preferred for respiratory tract infections.

Clindamycin and lincomycin are similar to each other and are more effective than erythromycin for treatment of infections caused by anaerobic bacteria. Anaerobic bacteria can grow in the absence of oxygen.


Symptoms should begin to improve within a few days of beginning to take this medicine. If they do not, or if they get worse, parents should 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.

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 occurs, 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 which can potentially include shock). If children develop these symptoms after taking azithromycin, they should stop taking the medicine and parents should get them immediate medical help.

Other rare side effects may occur with erythromycins and related drugs.


Erythromycins may interact with many other medicines. When interaction happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Parents of children taking erythromycins should let the physician know all other medicines their children are 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
  • antiseizure medicines such as valproic acid (Depakote, Depakene)
  • caffeine
  • antihistamine such as astemizole (Hismanal)
  • antiviral drugs such as zidovudine (Retrovir)

The list above does not include every drug that may interact with erythromycins. Parents should be sure to check with a physician or pharmacist before combining erythromycins with any other prescription or nonprescription (over-the-counter) medicine.

Some of the stomach upset caused by erythromycin can be minimized by changing the dosage form. Erythromycin is available as enteric-coated tablets, which are released in the intestine rather than the stomach; as a liquid; and as bead-filled capsules. These forms are less likely to cause stomach upset than traditional tablets.

Parental concerns

If a child has had an allergic reaction to erythromycin or any of its related drugs, the prescriber should be notified.

It is very important for patients to take erythromycins for as long as they have been prescribed. Patients must not stop taking the drug just because symptoms begin to improve. This point 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, patients should take the medicine in doses spaced evenly through the day and night. No doses should be missed. 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.

Liquid forms of erythromycin should be administered with a medicinal teaspoon or other measuring device. Household teaspoons vary in size and may give either too much or too little of the medication.

Bead-filled capsules may be opened and sprinkled on pudding or applesauce for ease of administration. Enteric-coated tablets should never be split or crushed, since doing so will destroy the effectiveness of the coating.

Parents should never ask physicians to prescribe antibiotics for children's illnesses. Antibiotics are important for appropriate infections but are seriously overprescribed. Overuse leads to needless expense for the parents, some discomfort and risk for the child, and the development of antibiotic-resistant bacteria, which have become a public health problem.

Children have complained about the bitter taste of clarithromycin oral liquid. This factor should not be considered a problem. Liquid medications that taste good may be mistaken for candy or sweets, and children may overdose themselves. All medications should be kept away from children.


Anaphylaxis —Also called anaphylactic shock; a severe allergic reaction characterized by airway constriction, tissue swelling, and lowered blood pressure.

Enteric coating —A coating or shell placed on a tablet that breaks up and releases the medicine into the intestine rather than the stomach.

Microorganism —An organism that is too small to be seen with the naked eye, such as a bacterium, virus, or fungus.

Respiratory system —The organs that are involved in breathing: the nose, the throat, the larynx, the trachea, the bronchi and the lungs. Also called the respiratory tract.

See also Pneumonia ; Penicillins .



Behrman Richard, Robert M. Kliegman, and Hal B. Jenson. Nelson Textbook of Pediatrics , 17th ed. Philadelphia: Saunders, 2003.

Mcevoy, Gerald K., et al. AHFS Drug Information 2004. Bethesda, MD: American Society of Healthsystems Pharmacists, 2004.

Siberry, George, and Robert Iannone, eds. The Harriet Lane Handbook , 15th ed. Philadelphia: Mosby, 2000.


Cunha, B. A. "Therapeutic implications of antibacterial resistance in community-acquired respiratory tract infections in children." Infection 32, no. 2 (April 2004): 98–108.

Gonzalez, B. E., et al. "Azithromycin compared with betalactam antibiotic treatment failures in pneumococcal infections of children." Pediatric Infectious Diseases Journal 23, no. 5 (May 2004): 399–405.

McIsaac, W. J., and T. To. "Antibiotics for lower respiratory tract infections: Still too frequently prescribed?" Canadian Family Physician 50 (April 2004): 569–575.


American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007–1098. Web site:

Office of Health Communication National Center for Infectious Diseases, Centers for Disease Control and Prevention. Mailstop C-14, 1600 Clifton Road Atlanta, GA 30333. Web site:


"Macrolides." Available online at (accessed September 29, 2004.)

Nancy Ross-Flanigan Samuel Uretsky, PharmD

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