Flagyl Side Effects

Generic Name: metronidazole

Please note - some side effects for Flagyl 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 - for the Consumer

Flagyl

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:

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.

Flagyl Capsules

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 Capsules:

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.

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.

Flagyl Side Effects - for the Professional

Flagyl Injection

Two serious adverse reactions reported in patients treated with intravenous metronidazole have been convulsive seizures and peripheral neuropathy, the latter characterized mainly by numbness or paresthesia of an extremity. Since persistent peripheral neuropathy has been reported in some patients receiving prolonged oral administration of metronidazole, patients should be observed carefully if neurologic symptoms occur and a prompt evaluation made of the benefit/risk ratio of the continuation of therapy.

The following reactions have also been reported during treatment with Metronidazole Injection, USP RTU®.

Gastrointestinal: Nausea, vomiting, abdominal discomfort, diarrhea and an unpleasant metallic taste.

Hematopoietic: Reversible neutropenia (leukopenia).

Dermatologic: Erythematous rash and pruritus.

Central Nervous System: Headache, dizziness, syncope, ataxia and confusion.

Local Reactions: Thrombophlebitis after intravenous infusion. This reaction can be minimized or avoided by avoiding prolonged use of indwelling intravenous catheters.

Other: Fever. Instances of a darkened urine have also been reported, and this manifestation has been the subject of a special investigation. Although the pigment which is probably responsible for this phenomenon has not been positively identified, it is almost certainly a metabolite of metronidazole and seems to have no clinical significance.

The following adverse reactions have been reported during treatment with oral metronidazole:

Gastrointestinal: Nausea, sometimes accompanied by headache, anorexia and occasionally vomiting; diarrhea, epigastric distress, abdominal cramping and constipation.

Mouth: A sharp, unpleasant metallic taste is not unusual. Furry tongue, glossitis and stomatitis have occurred; these may be associated with a sudden overgrowth of Candida which may occur during effective therapy.

Hematopoietic: Reversible neutropenia (leukopenia); rarely, reversible thrombocytopenia.

Cardiovascular: Flattening of the T-wave may be seen in electrocardiographic tracings.

Central Nervous System: Convulsive seizures, peripheral neuropathy, dizziness, vertigo, incoordination, ataxia, confusion, irritability, depression, weakness and insomnia.

Hypersensitivity: Urticaria, erythematous rash, flushing, nasal congestion, dryness of the mouth (or vagina or vulva) and fever.

Renal: Dysuria, cystitis, polyuria, incontinence, a sense of pelvic pressure and darkened urine.

Other: Proliferation of Candida in the vagina, dyspareunia, decrease of libido, proctitis and fleeting joint pains sometimes resembling “serum sickness.” If patients receiving metronidazole drink alcoholic beverages, they may experience abdominal distress, nausea, vomiting, flushing or headache. A modification of the taste of alcoholic beverages has also been reported. Rare cases of pancreatitis, which abated on withdrawal of the drug, have been reported.

Crohn's disease patients are known to have an increased incidence of gastrointestinal and certain extraintestinal cancers. There have been some reports in the medical literature of breast and colon cancer in Crohn's disease patients who have been treated with metronidazole at high doses for extended periods of time. A cause and effect relationship has not been established. Crohn's disease is not an approved indication for Metronidazole Injection, USP RTU®.

Side Effects by Body System

Other

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

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.

Gastrointestinal

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.

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.

Nervous system

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

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

Hypersensitivity

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

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.

Genitourinary

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

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