Along with its needed effects, erythromycin may cause some unwanted or undesirable effects. Generally, erythromycin is well tolerated and many people will not experience unwanted effects. The frequency and severity of these effects is dependant on many factors including dose, duration of therapy and individual susceptibility. Possible unwanted effects include:

• diarrhea
• nausea
• vomiting
• appetite loss
• stomach cramps

Uncommon:

• rash
• itching
• hives
• eczema

Rare:

• difficult breathing
• hearing loss (reversible)
• yellow discoloration of skin or eyes
• irregular or slow heartbeat

Erythromycin is an antibiotic. It inhibits the growth and replication of susceptible bacteria through blocking protein synthesis. This reduces bacterial growth or causes bacterial cell death. Erythromycin does not kill or suppress growth of all types of bacteria, but only those that have a sensitivity to this antibiotic. Infections caused by bacteria that are not sensitive to erythromycin will not show improvement after taking this medication.

Allergic reactions can occur with erythromycin use. People with a history of allergy, asthma, hay fever or hives seem to be more susceptible to these reactions. The reaction can be immediate and severe. Allergic symptoms include wheezing, hives, itching, swelling, joint and muscle pain, difficulty breathing, fever and skin rashes. Nausea and vomiting are not symptoms of an allergic reaction.
Taking the antibiotic repeatedly or for prolonged periods may result in bacterial or fungal overgrowth which can lead to a second infection. When this occurs, the erythromycin may need to be stopped and another antibiotic prescribed to treat the new infection.
Diarrhea often develops while taking erythromycin. This is sometimes caused by an overgrowth of bacteria in the gut that are not killed by the antibiotic. In severe cases, this may be life threatening and would require treatment with other antibiotics. In mild cases, symptoms disappear shortly after the drug is discontinued.
Drug Interactions: It is important to tell your doctor and pharmacist of any prescription or over-the-counter medications you are taking. In some cases the dose of one or both drugs may need to be altered or another drug may be prescribed.
The following drugs or drug classes have been known to interact with erythromycin.

• warfarin (e.g. Coumadin®)
• carbamazepine (e.g. Tegretol®)
• cyclosporine (e.g. Neoral®)
• clozapine (e.g. Clozaril®)
• digoxin (e.g. Lanoxin®)
• ergotamine (e.g. Cafergot®)
• theophylline (e.g. Theo-Dur®)
• triazolam (e.g. Halcion®)
• phenytoin (e.g. Dilantin®)
• cholesterol reducing medications (e.g. Lipitor®)

Use is not recommended in the following situations:

• allergy to erythromycin or any component of the preparation
• people concurrently taking ergot alkaloids and clozapine

Caution is recommended in the following situations:

• liver disease
• cardiac arrhythmias or QT prolongation

Use in pregnancy: Erythromycin crosses the placenta however, most erythromycins can be used in pregnancy.  The exception is erythromycin estolate which should not be used in the 2nd and 3rd trimesters.  Consult your doctor or pharmacist if you suspect you may be pregnant.

Use while breastfeeding: Erythromycin does pass into the breast-milk, but is considered safe to use.  Consult your doctor or pharmacist before you take erythromycin if you are breastfeeding.