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Metronidazole Side Effects Center
Medical Editor: John P. Cunha, DO, FACOEP
Metronidazole injection is an antibacterial drug used to treat serious infections caused by susceptible anaerobic bacteria. The brand name of this medication is discontinued, but generic versions may be available. Common side effects include dizziness, headache, diarrhea, nausea, vomiting, stomach upset, or a metallic taste in the mouth.
The loading dose of metronidazole injection is 15 mg/kg infused over one hour (approximately 1 g for a 70-kg adult), followed by a maintenance dose of 7.5 mg/kg infused over one hour every six hours (approximately 500 mg for a 70-kg adult). Metronidazole injection may interact with anticoagulants, phenytoin, phenobarbital, cimetidine, alcohol, and disulfiram. Tell your doctor all medications and supplements you use. During pregnancy, metronidazole injection should be used only if prescribed. Tell your doctor if you are pregnant before receiving treatment with metronidazole injection. This drug passes into breast milk. Consult your doctor before breastfeeding.
Our metronidazole injection Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
What is Prescribing information?
The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.
Metronidazole FDA Prescribing Information: Side Effects
The most serious adverse reactions reported in patients treated with metronidazole injection 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 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.
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: Encephalopathy, aseptic meningitis, convulsive seizures, optic neuropathy, peripheral neuropathy, dizziness, vertigo, incoordination, ataxia, confusion, dysarthria, irritability, depression, weakness and insomnia.
Hypersensitivity: Urticaria, erythematous rash, Stevens-Johnson Syndrome, flushing, nasal congestion, dryness of the mouth (or vagina or vulva) and fever.
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.
Read the entire FDA prescribing information for Metronidazole (Metronidazole Injection)
Additional Metronidazole Injection Information
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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