Flagyl ER Side Effects
Generic name: metronidazole
Medically reviewed by Drugs.com. Last updated on Jul 16, 2023.
Note: This document contains side effect information about metronidazole. Some dosage forms listed on this page may not apply to the brand name Flagyl ER.
For Healthcare Professionals
Applies to metronidazole: compounding powder, intravenous powder for injection, intravenous solution, oral capsule, oral suspension, oral tablet, oral tablet extended release.
General
The most serious side effects reported were convulsive seizures, encephalopathy, aseptic meningitis, optic neuropathy, and peripheral neuropathy (characterized by numbness/paresthesia of an extremity).[Ref]
Nervous system
Very common (10% or more): Headache (up to 18%)
Common (1% to 10%): Dysgeusia/taste perversion (e.g., metallic taste, sharp unpleasant metallic taste, taste of alcoholic beverages modified), dizziness
Rare (0.01% to 0.1%): Encephalopathy (e.g., confusion, fever, headache, hallucinations, paralysis, light sensitivity, disturbances in sight and movement, stiff neck), aseptic meningitis, seizure, somnolence, peripheral neuropathy, ataxia
Very rare (less than 0.01%): Subacute cerebellar syndrome (e.g., ataxia, dysarthria, gait impaired, nystagmus, tremor), drowsiness, convulsions, incoordination
Frequency not reported: Dysarthria, hypoesthesia, paresthesia, peripheral sensory neuropathy, transient epileptiform seizures, hearing impaired/hearing loss (including sensorineural), tinnitus, taste disorders/unpleasant taste in mouth, nystagmus, convulsive seizure, numbness, syncope, vertigo, paralysis[Ref]
Gastrointestinal
Very common (10% or more): Nausea (up to 10%)
Common (1% to 10%): Abdominal pain, diarrhea, dry mouth, stomatitis, glossitis
Rare (0.01% to 0.1%): Pancreatitis, upper abdominal pain/epigastralgia, vomiting
Frequency not reported: Constipation, tongue discoloration, oral mucositis, furry/furred tongue, gastrointestinal disturbances (e.g., epigastric pain/distress), proctitis, sudden overgrowth of Candida in mouth, abdominal cramping, dyspepsia, pseudomembranous colitis, mucositis[Ref]
Genitourinary
Very common (10% or more): Vaginitis (up to 15%)
Common (1% to 10%): Genital pruritus, abnormal urine, dysmenorrhea, moniliasis, urinary tract infection
Rare (0.01% to 0.1%): Chromaturia
Very rare (less than 0.01%): Darkened urine
Frequency not reported: Vaginal dryness, vulva dryness, dysuria, vaginal candidiasis, dyspareunia, polyuria, incontinence, cystitis, pyuria, proliferation of Candida in vagina[Ref]
Other
Common (1% to 10%): Bacterial infection, influenza-like symptoms
Uncommon (0.1% to 1%): Asthenia
Rare (0.01% to 0.1%): Mucosal inflammation, pyrexia/fever
Very rare (less than 0.01%): Flushing
Frequency not reported: Malaise, face edema, peripheral edema, chest pain, chills, overgrowth of Candida, disulfiram-like reaction, weakness, sensation of pelvic pressure[Ref]
Respiratory
Common (1% to 10%): Upper respiratory tract infection, rhinitis, sinusitis, pharyngitis
Frequency not reported: Dyspnea, nasal congestion, hiccup[Ref]
Musculoskeletal
Common (1% to 10%): Myalgia
Very rare (less than 0.01%): Arthralgia
Frequency not reported: Muscle spasms, fleeting joint pain, stiff neck[Ref]
Hematologic
Uncommon (0.1% to 1%): Leukopenia
Rare (0.01% to 0.1%): Neutropenia, thrombocytopenia, pancytopenia, agranulocytosis
Frequency not reported: Eosinophilia, bone marrow aplasia, bone marrow depression, blood dyscrasia[Ref]
Dermatologic
Rare (0.01% to 0.1%): Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema, erythema multiforme
Very rare (less than 0.01%): Skin rash, pustular eruptions, acute generalized exanthematous pustulosis, pruritus
Frequency not reported: Fixed drug eruption, swelling face, urticaria, hyperhidrosis, erythema, drug reaction with eosinophilia and systemic symptoms (DRESS), erythematosus rash, mild erythematous eruptions, pustulosis[Ref]
Hepatic
Rare (0.01% to 0.1%): Cholestatic hepatitis
Very rare (less than 0.01%): Increased liver enzymes (AST, ALT, alkaline phosphatase), cholestatic/mixed hepatitis, hepatocellular liver injury, jaundice, liver failure requiring liver transplant, abnormal liver function tests
Frequency not reported: Increased liver enzyme, hepatotoxicity/liver failure in patients with Cockayne syndrome, drug-induced hepatitis[Ref]
Hypersensitivity
Rare (0.01% to 0.1%): Anaphylaxis, anaphylactic shock, Jarisch-Herxheimer reaction
Frequency not reported: Serum sickness-like reaction, immediate/delayed hypersensitivity reactions, anaphylactic reaction, hypersensitivity
Psychiatric
Rare (0.01% to 0.1%): Hallucinations
Very rare (less than 0.01%): Confusion/confusional state, psychotic disorders
Frequency not reported: Depression, insomnia, depressed mood, decreased libido, irritability, psychosis, disorientation, psychotic reaction[Ref]
Ocular
Rare (0.01% to 0.1%): Optic neuropathy, diplopia, myopia
Very rare (less than 0.01%): Vision disorders (e.g., diplopia, myopia)
Frequency not reported: Optic neuropathy/neuritis, saccadic eye movement, blurred vision, decreased visual acuity, changed color vision, light sensitivity[Ref]
Cardiovascular
Frequency not reported: Flattening of T-wave on ECG, tachycardia, palpitations, QT interval prolonged on ECG[Ref]
Metabolic
Frequency not reported: Anorexia, decreased appetite[Ref]
Oncologic
Frequency not reported: Breast cancer, colon cancer, gastrointestinal cancer, certain extraintestinal cancers[Ref]
An increased incidence of gastrointestinal and certain extraintestinal cancers have been reported in patients with Crohn's disease. Breast and colon cancer have been reported in medical literature in Crohn's disease patient treated with high doses of this drug for a prolonged duration; causality was not established.[Ref]
Local
Frequency not reported: Injection site reaction, thrombophlebitis[Ref]
Frequently asked questions
- What happens if you drink alcohol with metronidazole?
- What are the most common skin conditions? (with photos)
- How long does it take for metronidazole to work?
- Can metronidazole cause a yeast infection?
- What can I do about the metallic taste of Flagyl?
- Does metronidazole treat chlamydia?
- Does Flagyl cause diarrhea?
- Can you have sex while taking metronidazole?
- How long does it take metronidazole to leave your system?
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References
1. Product Information. Flagyl (metronidazole). Searle. 2002;PROD.
2. Cerner Multum, Inc. UK Summary of Product Characteristics.
3. Cerner Multum, Inc. Australian Product Information.
Further information
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Some side effects may not be reported. You may report them to the FDA.