"A family of bacteria has become increasingly resistant to last-resort antibiotics during the past decade, and more hospitalized patients are getting lethal infections that, in some cases, are impossible to cure.Â The findings, published today"...
In two multicenter clinical trials, a total of 270 patients received 750 mg Flagyl ER (metronidazole extended release tablets) tablets orally once daily for 7 days, and 287 were treated with a comparator agent administered intravaginally once daily for 7 days. (See Clinical Studies.)4,5
Most adverse events were described as being of mild or moderate severity. Among patients taking Flagyl ER (metronidazole extended release tablets) who reported headaches, 10% considered them severe, and less than 2% of reported episodes of nausea were considered severe. Metallic taste was reported by 9% of patients taking Flagyl ER (metronidazole extended release tablets) .
Adverse events reported at ≥ 2% incidence for either treatment group, irrespective of treatment causality, are summarized in the table below.
Adverse Events ( ≥ 2% Incidence Rate)—Irrespective of Treatment
|Flagyl ER 7 days
|Headache||48 (18%)||44 (15%)|
|Vaginitis||39 (15%)||32 (12%)|
|Nausea||28 (10%)||8 (3%)|
|Taste Perversion (metallic taste)||23 (9%)||1 (0%)|
|Infection Bacterial||19 (7%)||17 (6%)|
|Influenza-like Symptoms||17 (6%)||20 (7%)|
|Pruritus Genital||14 (5%)||25 (9%)|
|Abdominal Pain||10 (4%)||13 (5%)|
|Dizziness||11 (4%)||3 (1%)|
|Diarrhea||11 (4%)||3 (1%)|
|Upper Respiratory Tract Infection||11 (4%)||10 (4%)|
|Rhinitis||12 (4%)||10 (4%)|
|Sinusitis||7 (3%)||6 (2%)|
|Urine Abnormal||7 (3%)||4 (1%)|
|Pharyngitis||8 (3%)||4 (1%)|
|Dysmenorrhea||9 (3%)||7 (2%)|
|Moniliasis||9 (3%)||8 (3%)|
|Mouth Dry||5 (2%)||2 (1%)|
|Urinary Tract Infection||6 (2%)||16 (6%)|
Vulvovaginal candidiasis is a recognized consequence of treatment with many anti-infective agents. In these multicenter clinical trials, there were no statistically significant differences in the incidence rates of yeast vaginitis for groups of patients treated with Flagyl ER (metronidazole extended release tablets) or the vaginal comparator.
The following reactions have also been reported during treatment with metronidazole:
Central Nervous System
The most serious adverse reactions reported in patients treated with metronidazole have been convulsive seizures, encephalopathy, aseptic meningitis, optic 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 administration of metronidazole, patients should be specifically warned about these reactions and should be told to stop the drug and report immediately to their physicians if any neurologic symptoms occur. In addition, patients have reported dizziness, vertigo, incoordination, ataxia, confusion, dysarthria, irritability, depression, weakness, and insomnia. (See WARNINGS.)
The most common adverse reactions reported have been referable to the gastrointestinal tract, particularly nausea reported by about 12% of patients, sometimes accompanied by headache, anorexia, and occasionally vomiting, diarrhea, epigastric distress, and abdominal cramping. Constipation has also been reported.
Furry tongue, glossitis, and stomatitis have occurred; these may be associated with a sudden overgrowth of Candida which may occur during therapy. Rare cases of pancreatitis, which generally abated on withdrawal of the drug, have been reported.
Flattening of the T-wave may be seen in electrocardiographic tracings.
Dysuria, cystitis, polyuria, incontinence, and a sense of pelvic pressure. Instances of darkened urine have been reported by approximately one patient in 100,000. 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.
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.
Patients with Crohn's disease 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 Flagyl ER 750 mg tablets.
Read the Flagyl ER (metronidazole extended release tablets) Side Effects Center for a complete guide to possible side effects »
Metronidazole has been reported to potentiate the anticoagulant effect of warfarin and other oral coumarin anticoagulants, resulting in a prolongation of prothrombin time. This possible drug interaction should be considered when metronidazole is prescribed for patients on this type of anticoagulant therapy.
The simultaneous administration of drugs that induce microsomal liver enzymes, such as phenytoin or phenobarbital, may accelerate the elimination of metronidazole, resulting in reduced plasma levels; impaired clearance of phenytoin has been reported.
The simultaneous administration of drugs that decrease microsomal liver enzyme activity, such as cimetidine, may prolong the half-life and decrease plasma clearance of metronidazole. In patients stabilized on relatively high doses of lithium, short-term metronidazole therapy has been associated with elevation of serum lithium and, in a few cases, signs of lithium toxicity. Serum lithium and serum creatinine levels should be obtained several days after beginning metronidazole to detect any increase that may precede clinical symptoms of lithium intoxication.
Alcoholic beverages should not be consumed during metronidazole therapy and for at least three days afterward because abdominal cramps, nausea, vomiting, headaches, and flushing may occur.
Psychotic reactions have been reported in alcoholic patients who are using metronidazole and disulfiram concurrently. Metronidazole should not be given to patients who have taken disulfiram within the last 2 weeks.
Drug/Laboratory test interactions
Metronidazole may interfere with certain types of determinations of serum chemistry values, such as aspartate aminotransferase (AST, SGOT), alanine aminotransferase (ALT, SGPT), lactate dehydrogenase (LDH), triglycerides, and hexokinase glucose. Values of zero may be observed. All of the assays in which interference has been reported involve enzymatic coupling of the assay to oxidation-reduction of nicotinamide adenine dinucleotide (NAD+⇔NADH). Interference is due to the similarity in absorbance peaks of NADH (340 nm) and metronidazole (322 nm) at pH 7.
4. Integrated clinical and statistical report for the treatment of bacterial vaginosis with metronidazole modified release tablet— a dose duration study. G.D. Searle & Co., Protocol No. N13-95-02-015; Report No. N13-96-06-015, 19 Nov 1996.
5. Integrated clinical and statistical report for the treatment of bacterial vaginosis with metronidazole modified release tablet. G.D. Searle & Co., Protocol No. N13-95-02-017; Report No. N13-96-06-017, 11 Nov 1996.
Last reviewed on RxList: 9/15/2010
This monograph has been modified to include the generic and brand name in many instances.
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