Along with its needed effects, clarithromycin may cause some unwanted or undesirable effects. Generally, clarithromycin 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
• abnormal taste
• stomach discomfort
• indigestion

Uncommon:

• allergy (e.g. hives, itching, rash, difficulty breathing)
• headache
• dizziness
• constipation
• diaper rash
• oral candidiasis (thrush)
• vomiting

Rare:

• jaundice (yellowing of skin or eyes)
• difficulty breathing
• confusion
• hallucinations
• nightmares

Clarithromycin is an antibiotic. It works by suppressing formation of vital proteins in bacteria, slowing bacterial growth. Clarithromycin does not 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 clarithromycin will not show improvement after taking this medication.

Allergic reactions can occur with clarithromycin use. The reaction can be immediate and severe. Allergic symptoms include wheezing, hives, itching, swelling, spasms in the throat and breathing tubes, 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 clarithromycin may need to be stopped and another antibiotic prescribed to treat the new infection.
Diarrhea often develops while taking clarithromycin. 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. Interactions have been known to occur with the following drugs and drug classes.

• anticoagulants (e.g. Coumadin®)
• carbamazepine (e.g. Tegretol®)
• cyclosporine (e.g. Neoral®)
• digoxin (e.g. Lanoxin®)
• disopyramide (e.g. Norpace®)
• ergot-containing drugs (e.g. Ergomar®)
• fluconazole (e.g. Diflucan®)
• pimozide (e.g. Orap®)
• zidovudine (e.g. Retrovir®)
• theophylline (e.g. Theo-Dur®)
• triazolam (e.g. Halcion®)
• phenytoin (e.g. Dilantin®)
• cholesterol reducing medications such as atorvastatin (e.g. Lipitor®), lovastatin (e.g. Mevacor®)

Use is not recommended in the following situations:

• allergy to clarithromycin, erythromycin or any of the macrolide antibiotics

Caution is recommended in the following situations:

• kidney disease, severe
• liver disease or dysfunction
• myasthenia gravis

Use in pregnancy: Clarithromycin should not be used during pregnancy, especially during the first trimester unless there are no safer alternatives.  Consult your doctor or pharmacist if you suspect that you may be pregnant.

Use while breastfeeding: Clarithromycin passes into the breast-milk, but is considered safe for use if breastfeeding. Consult your doctor or pharmacist before use.