Flagyl ER Side Effects

Generic name: metronidazole

Generic Name: Metronidazole

Please note - some side effects for Flagyl ER may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA at http://www.fda.gov/medwatch/ or 1-800-FDA-1088 (1-800-332-1088).

Side Effects of Flagyl ER - for the consumer

Flagyl ER Extended-Release Tablets

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 when using Flagyl ER Extended-Release Tablets:

Appetite loss; constipation; diarrhea; dizziness; headache; metallic taste; nausea; stomach upset; vomiting.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); bloody stools; increased or decreased urination; numbness, tingling, or burning of your arms, hands, legs, or feet; seizures; severe diarrhea; sore throat, chills, or fever; stomach pain or cramps; vaginal itching, odor, or discharge; white patches in the mouth.

By body system

Other side effects

A disulfiram-like reaction has been reported in some patients drinking ethanol while taking metronidazole. Patients have experienced flushing, nausea, headache, and hypotension. Patients should be advised to refrain from all forms of ethanol while taking metronidazole and for at least 72 hours after the last dose.

Metronidazole may produce a disulfiram-like reaction when taken concurrently with ethanol.

Gastrointestinal side effects

Gastrointestinal side effects of metronidazole have been common and have included nausea (up to 12%), anorexia, dry mouth, a strange metallic taste, diarrhea, vomiting, epigastric distress, abdominal cramping, and coating of the tongue. Rarely, metronidazole has been associated with pseudomembranous colitis and pancreatitis.

Although metronidazole has been used to treat pseudomembranous colitis, it has rarely also been implicated as a causative agent. These rare cases have been successfully treated with vancomycin.

Nervous system side effects

Central nervous system effects of metronidazole have included encephalopathy resulting in dizziness, confusion, disorientation, agitation, and hallucinations. Peripheral neuropathy, seizures, ataxia, reversible abnormalities in the cerebellar dentate nuclei, and aseptic meningitis have also been reported.

A rare but serious adverse effect of metronidazole is peripheral neuropathy which is thought to be related to dose and duration of therapy. Most cases occur after doses of 1000 to 2400 mg per day for at least 30 days, or a total dose of 50 grams. Neuropathy is generally located in the lower extremities and presents with numbness, tingling, and paresthesias. Patients should be advised to discontinue metronidazole if they experience these effects. Neuropathy may be persistent despite discontinuation of metronidazole. Seizures associated with metronidazole are rare, but do occur.

Several cases of MRI abnormalities of the dentate nuclei associated with symptoms of ataxia and dysarthria have been reported. The symptoms and dentate nuclei lesions resolved several weeks after discontinuation of metronidazole. These symptoms and metronidazole-induced lesions in the brain stem and cerebellar nuclei have also been described in rat studies.

Hematologic side effects

Hematologic adverse effects of metronidazole have rarely been reported and include reversible leukopenia and thrombocytopenia.

Hypersensitivity side effects

Hypersensitivity reactions to metronidazole have occurred as urticaria, rash, and pruritus. A serum sickness-like reaction has been reported. Fixed drug eruptions have been reported and cross-sensitivity to other nitroimidazole derivatives has been demonstrated.

Metronidazole has rarely been associated with a serum sickness-like reaction which presents as arthralgias, malaise, fever, chills, pruritus, and rash.

Genitourinary side effects

Genitourinary side effects have included vaginal candidiasis, vaginal itching, and dark urine.

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