Do NOT use Flagyl ER if:

• you are allergic to any ingredient in Flagyl ER or to another nitroimidazole (eg, tinidazole)
• you are in the first trimestr of pregnancy
• you are taking busulfan, an ergot alkaloid (eg, ergotamine), or you have taken disulfiram within the past 2 weeks
• you are taking an HIV protease inhibitor that contains alcohol (eg, amprenavir solution); check with your pharmacist if you are unsure if the medicine contains alcohol
• you drink alcohol.

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

Some medical conditions may interact with Flagyl ER. 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 nerve, brain, or blood problems; Crohn disease; or a history of liver problems or seizures.

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

• Disulfiram because side effects, such as mental or mood changes, may occur
• Amiodarone because the risk of irregular heartbeat may be increased
• Barbiturates (eg, phenobarbital) or phenytoin because they may decrease Flagyl ER's effectiveness
• Anticoagulants (eg, warfarin), busulfan, cyclosporine, ergot alkaloids (eg, ergotamine), HIV protease inhibitors containing alcohol (eg, amprenavir solution ), lithium, or macrolide immunosuppressants (eg, tacrolimus) because the risk of their side effects may be increased by Flagyl ER.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Flagyl ER 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:

• Flagyl ER may cause dizziness. This effect may be worse if you take it with alcohol or certain medicines. Use Flagyl ER with caution. Do not drive or perform other possibly unsafe tasks until you know how you react to it.
• Do not drink alcohol while you are taking Flagyl ER and for at least 3 days after the last dose.
• 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.
• Flagyl ER only works against bacteria; it does not treat viral infections (eg, the common cold).
• Be sure to use Flagyl ER 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.
• Long-term or repeated use of Flagyl ER 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.
• Flagyl ER may interfere with certain lab tests. Be sure your doctor and lab personnel know you are taking Flagyl ER.
• Lab tests, including liver function and white blood cell counts, may be performed while you use Flagyl ER. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
• Use Flagyl ER with caution in the elderly; they may be more sensitive to its effects.
• Flagyl ER should be used with extreme caution 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 Flagyl ER while you are pregnant. Do not use Flagyl ER in the first 3 months of pregnancy. Flagyl ER is found in breast milk. Do not breastfeed while taking Flagyl ER.

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:

Appetite loss; constipation; diarrhea; dizziness; headache; metallic taste; nausea; stomach upset; 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); bloody stools; decreased coordination; increased or decreased urination; numbness, tingling, or burning of the arms, hands, legs, or feet; red, swollen, blistered, or peeling skin; seizures; severe diarrhea; severe or persistent dizziness or headache; sore throat, chills, or fever; speech problems; stiff neck; stomach pain or cramps; vaginal itching, odor, or discharge; vision loss or other vision changes; white patches in the mouth.

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.