Do NOT use Zithromax if:

• you are allergic to any ingredient in Zithromax, to other macrolide antibiotics (eg, erythromycin), or to ketolide antibiotics (eg, telithromycin)
• you are taking dofetilide, nilotinib, pimozide, propafenone, or tetrabenazine.

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with Zithromax. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

• if you are pregnant, planning to become pregnant, or are breast-feeding
• if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• if you have allergies to medicines, foods, or other substances
• if you have liver or kidney problems, myasthenia gravis, or abnormal heart rhythms.

Some medicines may interact with Zithromax. Tell your health care provider if you are taking any other medicines, especially any of the following:

• Antiarrhythmics (eg, disopyramide, dofetilide ), arsenic, astemizole, cisapride, domperidone, maprotiline, methadone, paliperidone, pimozide, propafenone, quinolone antibiotics (eg, levofloxacin), terfenadine, or tetrabenazine because the risk of heart problems, including irregular heartbeat, may be increased
• Nelfinavir because it may increase the risk of Zithromax's side effects
• Rifampin because it may decrease Zithromax's effectiveness
• Anticoagulants (eg, warfarin), carbamazepine, cyclosporine, digoxin, ergot derivatives (eg, ergotamine), nilotinib, phenytoin, rifampin, theophylline, triazolam, or tyrosine kinase receptor inhibitors (eg, dasatinib) because the risk of their side effects may be increased by Zithromax.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Zithromax may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

Important safety information:

• Zithromax may cause drowsiness, dizziness, blurred vision, or lightheadedness. These effects may be worse if you take it with alcohol or certain medicines. Use Zithromax with caution. Do not drive or perform other possible unsafe tasks until you know how you react to it.
• Zithromax may cause you to become sunburned more easily. Avoid the sun, sunlamps, or tanning booths until you know how you react to Zithromax. Use a sunscreen or wear protective clothing if you must be outside for more than a short time.
• Mild diarrhea is common with antibiotic use. However, a more serious form of diarrhea (pseudomembranous colitis) may rarely occur. This may develop while you use the antibiotic or within several months after you stop using it. Contact your doctor right away if stomach pain or cramps, severe diarrhea, or bloody stools occur. Do not treat diarrhea without first checking with your doctor.
• Tell your doctor or dentist that you take Zithromax before you receive any medical or dental care, emergency care, or surgery.
• Long-term or repeated use of Zithromax may cause a second infection. Tell your doctor if signs of a second infection occur. Your medicine may need to be changed to treat this.
• Be sure to use Zithromax for the full course of treatment. If you do not, the medicine may not clear up your infection completely. The bacteria could also become less sensitive to this or other medicines. This could make the infection harder to treat in the future.
• Zithromax only works against bacteria; it does not treat viral infections (eg, the common cold).
• Zithromax should not be used in children; safety and effectiveness in children have not been confirmed.
• Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Zithromax while you are pregnant. It is not known if Zithromax is found in breast milk. If you are or will be breast-feeding while you use Zithromax, check with your doctor. Discuss any possible risks to your baby.

All medicines may cause side effects, but many people have no, or minor, side effects.

Check with your doctor if any of these most common side effects persist or become bothersome:

Diarrhea; headache; loose stools; nausea; stomach pain; upset stomach; vomiting.

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue; unusual hoarseness); bloody stools; changes in hearing or hearing loss; chest pain; eye or vision problems; irregular heartbeat; muscle weakness; pounding in the chest; red, swollen, blistered, or peeling skin; ringing in the ears; seizure; severe diarrhea; stomach cramps/pain; trouble speaking or swallowing; yellowing of the skin or eyes.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.