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What is Flagyl (metronidazole), and what is it used for?
- Giardia infections of the small intestine,
- amebic liver abscess,
- amebic dysentery,
- bacterial vaginosis,
- trichomonas vaginal infections,
- carriers of trichomonas (both sexual partners) who do not have symptoms of infection;
- abscesses in the
- abdomen, and
- C. difficile (C. diff) diarrhea;
- Helicobacter pylori (H. pylori) that causes stomach or intestinal ulcers; and
- acne rosacea.
Common side effects of Flagyl and Flagyl ER include
- loss of appetite,
- rash (rare),
- abdominal cramps,
- dry mouth,
- dark-colored urine,
- metallic taste in mouth,
- weight loss,
- furry tongue,
- nasal congestion,
- flushing, and
- vaginal dryness.
Serious side effects of Flagyl and Flagyl ER include brain disease, fevers, mouth sores, painful urination, nerve damage resulting in prickling or tingling sensations that may become permanent, cystitis, pelvic pain or pressure, decreased sex drive, inflammation of the lining of the rectum, inflammation of the mouth and lips, inflammation of the tongue, seizures, numbness and tingling of extremities, encephalopathy, aseptic meningitis, and colon cancer in people with Crohn's disease.
Drug interactions with Flagyl and Flagyl ER include alcohol, warfarin, cimetidine, cholestyramine, amprenavir, propylene glycol, carbamazepine, lithium, and cyclosporine. Flagyl and Flagyl ER should not be used in early pregnancy because of potential adverse effects on the fetus. Flagyl and Flagyl ER are excreted in breast milk. Because of potential adverse effects on the newborn, females who are nursing should not use metronidazole.
What are the important side effects of Flagyl (metronidazole)?
Flagyl is a useful antibiotic and is generally well tolerated with appropriate use.
The most common and minor side effects include:
- Loss of appetite
- A metallic taste
- Rarely a rash
- Abdominal cramps
- Dry mouth
- Dark-colored urine
- Metallic taste in mouth
- Weight loss (anorexia)
- Furry tongue
- Nasal congestion
- Vaginal dryness
Side effects that are uncomfortable, but may become serious include:
- Brain disease
- Mouth sores
- Pain with urination
- Prickling or tingling sensations that may become permanent
- Pelvic pain or pressure
- Decrease of libido
Serious side effects of Flagyl are rare and the drug should be stopped if these symptoms appear:
Flagyl (metronidazole) side effects list for healthcare professionals
The following reactions have 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 headache, syncope, dizziness, vertigo, incoordination, ataxia, confusion, dysarthria, irritability, depression, weakness, and insomnia.
The most common adverse reactions reported have been referable to the gastrointestinal tract, particularly nausea, sometimes accompanied by headache, anorexia, and occasionally vomiting; diarrhea; epigastric distress; and abdominal cramping and constipation.
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 therapy.
Erythematous rash and pruritus.
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.” Rare cases of pancreatitis, which generally abated on withdrawal of the drug, have 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 tablets.
What drugs interact with Flagyl (metronidazole)?
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 two weeks.
Warfarin And other Oral Anticoagulants
Metronidazole has been reported to potentiate the anticoagulant effect of warfarin and other oral coumarin anticoagulants, resulting in a prolongation of prothrombin time. When Flagyl is prescribed for patients on this type of anticoagulant therapy, prothrombin time and INR should be carefully monitored.
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.
Metronidazole has been reported to increase plasma concentrations of busulfan, which can result in an increased risk for serious busulfan toxicity. Metronidazole should not be administered concomitantly with busulfan unless the benefit outweighs the risk. If no therapeutic alternatives to metronidazole are available, and concomitant administration with busulfan is medically needed, frequent monitoring of busulfan plasma concentration should be performed and the busulfan dose should be adjusted accordingly.
Drugs That Inhibit CYP450 Enzymes
Drugs That Induce CYP450 Enzymes
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 also been reported.
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 glucose hexokinase. 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.
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Related Disease Conditions
Bacterial Vaginosis (BV)
Bacterial vaginosis is an abnormal vaginal condition with signs and symptoms of vaginal discharge, vaginal odor, and vaginal pain. Bacterial vaginosis results from an overgrowth of normal bacteria in the vagina. Although it may cause some disturbing symptoms (discharge and odor), it is not dangerous and cannot be passed by sex. Diagnosis becomes important to exclude serious infections like gonorrhea and Chlamydia. Many treatment options are available such as oral antibiotics and vaginal gels.
Giardiasis (Giardia lamblia) is a parasite responsible for a common form of infectious diarrhea. The parasite lives in two stages: trophozoites and cysts. People at risk for giardiasis are those that live in areas where there is inadequate sanitation or treatment of drinking water. Giardiasis also is a common cause of outbreaks of diarrhea in day-care centers. Symptoms and signs of giardiasis include abdominal pain, stomach cramping, bloating, nausea, and fatigue. Treatment for giardiasis is with antibiotic medication.
Trichomoniasis is a sexually transmitted disease (STD) caused by a parasite passed from person to person. Trichomoniasis can be picked up from contact with damp, moist objects like towels, wet clothing, or toilet seat. Symptoms include yellow, green, or gray vaginal discharge with a strong odor, painful intercourse or urination, genital irritation and itching, and lower abdominal pain. Antibiotics are the only treatment to cure trichomoniasis.
Clostridium Difficile Colitis (C. diff, C. difficle Colitis)
Clostridium difficile (C. difficile) is a bacterium, and is one of the most common causes of infection of the colon. C. difficile spores are found frequently in hospitals, nursing homes, extended care facilities, and nurseries for newborn infants.
Treatment & Diagnosis
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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.
Healthcare professional and drug interactions sections courtesy of the U.S. Food and Drug Administration.
Top Flagyl metronidazole Side Effects Related Articles
Bacterial VaginosisBacterial vaginosis is an abnormal vaginal condition with signs and symptoms of vaginal discharge, vaginal odor, and vaginal pain. Bacterial vaginosis results from an overgrowth of normal bacteria in the vagina. Although it may cause some disturbing symptoms (discharge and odor), it is not dangerous and cannot be passed by sex. Diagnosis becomes important to exclude serious infections like gonorrhea and Chlamydia. Many treatment options are available such as oral antibiotics and vaginal gels.
Children's Abdominal PainAbdominal pain in children can be more than just a tummy ache. What are the common causes of abdominal pain in children? Learn about pediatric abdominal pain symptoms like rash, vomiting, diarrhea, and fever. What is the best treatment for stomach pain in children?
Cipro vs. FlagylCipro, generic name ciprofloxacin, is an antibiotic that belongs to a class of antibiotics called fluoroquinolones, prescribed for the treatment a variety of bacterial infections. Flagyl, generic name metronidazole, is an antibiotic prescribed for the treatment of parasites and anaerobic bacteria. Review side effects, dosage, drug interactions, and pregnancy and breastfeeding safety information prior to using these antibiotics.
Clostridium Difficile Colitis (Antibiotic-Associated Colitis, C. difficile colitis)
Clostridium difficile (C. difficile) is a bacterium, and is one of the most common causes of infection of the colon. C. difficile spores are found frequently in hospitals, nursing homes, extended care facilities, and nurseries for newborn infants. They can be found:
- on bedpans,
- toilet seats,
- rooms, and
- diaper pails.
They even can be carried by pets. Antibiotic-associated (C. difficile) colitis is an infection of the colon caused by C. difficile that occurs primarily among individuals who have been using antibiotics. Treatment for C. difficile colitis includes:
- replenishment of electrolyte deficiencies,
- discontinuing the antibiotic that caused the colitis, and
- using antibiotics to eradicate the C. difficile bacterium.
Giardia LambliaGiardiasis (Giardia lamblia) is a parasite responsible for a common form of infectious diarrhea. The parasite lives in two stages: trophozoites and cysts. People at risk for giardiasis are those that live in areas where there is inadequate sanitation or treatment of drinking water. Giardiasis also is a common cause of outbreaks of diarrhea in day-care centers. Symptoms of giardiasis include
- abdominal pain,
- stomach cramping,
- nausea, and
Metrogel (metronidazole) Side EffectsMetrogel, Metrocream, and Metrogel Vaginal (metronidazole topical) is an antibiotic effective against anaerobic bacteria and certain parasites. Metrogel and Metrocream topical gel, cream, and lotion are used for treating rosacea. Metrogel Vaginal is used to treat bacterial vaginosis.
metronidazole (Flagyl, Flagyl ER) AntibioticMetronidazole (Flagyl, Flagyl ER) is a prescription antibiotic medication prescribed for the treatment of a variety of parasitic and bacterial infections of the vagina, gynecological area, skin, intra-abdominal cavity, blood, bone, joint, nervous system, and heart. For example, giardia, bacterial vaginosis, pelvic inflammatory disease (PID), C. difficile, H. pylori, STDs (trichomonas), acne rosacea, peritonitis, endometriosis, endomyometritis, tubo-ovarian abscess, bacterial septicemia, meningitis, brain abscess, pneumonia, lung abscess, and endocarditis.
Metronidazole (Flagyl) vs. azelaic acid (Finacea)
Metronidazole and azelaic acid are antibiotics used to treat acne. Brand names for metronidazole include Flagyl and Flagyl ER and brand names for azelaic acid include Finacea and Azelex. A difference is metronidazole is taken orally and azelaic acid is used topically (on the skin).
Metronidazole (Flagyl) vs. Clindamycin (Cleocin)
Metronidazole (Flagyl) and clindamycin (Cleocin) phosphate vaginal cream are antibiotics used to treat vaginal infections. A difference is metronidazole is taken orally and clindamycin phosphate vaginal cream is used topically (on the skin).
Metronidazole (Flagyl) vs. Fluconazole (Diflucan)
Metronidazole and fluconazole are used to treat different types of vaginal infections. Metronidazole is an antibiotic used to treat bacterial vaginosis and trichomonas vaginal infections, and fluconazole is an antifungal used to treat vaginal fungal infections caused by Candida.
Metronidazole vs. KetoconazoleMetronidazole and ketoconazole are used to treat different kinds of infections. Metronidazole is used to treat parasitic infections including Giardia infections of the small intestine, amebic liver abscess, amebic dysentery, bacterial vaginosis, trichomonas vaginal infections, and carriers of trichomonas who do not have symptoms of infection; to treat abscesses in the liver, pelvis, abdomen, and brain; among others. Metronidazole topical gel is used for treating acne rosacea and metronidazole vaginal gel is used for treating bacterial vaginosis.
Stomach Flu: What You Need to KnowIt can take you by surprise and leave you drained and exhausted. The “stomach flu” usually goes away on its own, but it can cause dehydration and other health problems.
Trichomoniasis is a sexually transmitted disease (STD) caused by a parasite passed from person to person. Trichomoniasis can be picked up from contact with damp, moist objects like towels, wet clothing, or toilet seat. Symptoms include
- yellow, green, or gray vaginal discharge with a strong odor,
- painful intercourse or urination,
- genital irritation and itching, and
- lower abdominal pain.
Antibiotics are the only treatment to cure trichomoniasis.
Tummy Trouble QuizTummy Troubles? Get a better idea of what's causing the nausea, vomiting, bloating, gas, constipation, diarrhea, pain, and other gastrointestinal discomforts and problems. Take the Tummy Troubles Quiz!