6 Metronidazole Side Effects You Should Know About
Metronidazole is an antibiotic used to treat bacterial and protozoal infections. Side effects of metronidazole can include headaches, taste changes, and nausea.
metronidazole
Used for Amoebiasis, Bacterial Infection, Diarrhea, Gastrointestinal Infection, Lower Respiratory Infection, Meningitis, Parasitic Infection, Skin Infection
Used for Amoebiasis, Bacterial Infection, Diarrhea, Gastrointestinal Infection, Lower Respiratory Infection, Meningitis, Parasitic Infection, Skin Infection
Metronidazole (Flagyl) is an oral antibiotic for adults and children. It's used to treat certain bacterial and parasitic infections, including bacterial vaginosis (a type of vaginal bacteria infection) and trichomoniasis (a sexually transmitted infection, or STI). Metronidazole (Flagyl) is taken by mouth, typically 3 times a day. Some common side effects of this medication include diarrhea, nausea, and vomiting. Avoid drinking alcohol while taking and for 3 days after stopping metronidazole (Flagyl) because this combination can cause a serious reaction. Metronidazole (Flagyl) is available as a lower-cost generic.
What is Metronidazole (Flagyl)?
What is Metronidazole (Flagyl) used for?
Treatment of certain bacterial and parasitic infections, including:
- Trichomoniasis
- Amebiasis (parasitic gut infection)
- Serious bacterial infections, such as:
- Abdominal infection (including peritonitis)
- Skin infections
- Gynecological infections (including endometritis)
- Bloodstream infection (septicemia)
- Bone and joint infections
- Central nervous system infections (meningitis)
- Lung infections (lower respiratory tract infections)
- Heart infection (endocarditis)
How Metronidazole (Flagyl) works
Metronidazole (Flagyl) is a nitroimidazole antibiotic. It kills bacteria and parasites by damaging their genetic material.
When does Metronidazole (Flagyl) start working?Time passed since treatment started:
Drug facts
| Common Brands | Flagyl |
|---|---|
| Drug Class | Nitroimidazole antibiotic |
| Controlled Substance Classification | Not a controlled medication |
| Generic Status | Lower-cost generic available |
| Availability | Prescription only |
More on Metronidazole (Flagyl) essentials
Side effects of Metronidazole (Flagyl)
The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.
Common Side Effects
Please note: These are common side effects reported by people who took extended-release metronidazole (Flagyl)
- Headache (18%)
- Inflammation of the vagina (15%)
- Nausea (10%)
- Metallic taste (9%)
- Flu-like symptoms (6%)
Less Common Side Effects
- Itchy groin
- Belly pain
- Dizziness
- Diarrhea
- Upper respiratory infection
- Sinus infection
- Stuffy nose
- Sore throat
- Dry mouth
- Urinary tract infection
Metronidazole (Flagyl) serious side effects
Contact your healthcare provider immediately if you experience any of the following.
- Brain and nerve problems: seizures, numbness in the feet and hands, pain when moving the eye, headache, dizziness, vertigo, impaired coordination, slurred speech, easily irritable, depression, weakness, trouble sleeping
- Severe allergic or skin reaction: rash, blistering or peeling of skin, hives, painful sores in your mouth or around your eyes, fever, trouble breathing, swollen lymph nodes
- Kidney problems: feeling sick or weak, urinating less than usual, confusion, blood in urine, swelling in the legs, ankles, or feet
- Liver problems: pain in the right side of the stomach, yellowing of the whites of the eyes or skin, dark-colored urine, light-colored stool
When do Metronidazole (Flagyl) possible side effects begin and end?
Time passed since treatment started:
M
H
D
W
M
Nausea or vomiting
Diarrhea
Stomach pain
Low appetite
Metallic taste in the mouth
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The following Metronidazole (Flagyl) side effects have also been reported
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
More common
Agitation
back pain
blindness
blurred vision
burning, numbness, tingling, or painful sensations in the hands or feet
changes in speech patterns
confusion
decreased vision
dizziness
drowsiness
headache
irritability
lack of coordination
seeing or hearing things that are not there
seizures
shakiness and unsteady walk
slurred speech
stiff neck or back
trouble speaking
unsteadiness, trembling, or other problems with muscle control or coordination
unusual tiredness or weakness
vomiting
weakness in the arms, hands, legs, or feet
Less common
Black, tarry stools
blood in the urine
body aches or pain
burning while urinating
chills
clumsiness or unsteadiness
difficulty with breathing
ear congestion
fainting
feeling of pelvic pressure
frequent or painful urination
irregular heartbeat
loss of voice
pinpoint red spots on the skin
skin rash, hives, redness, itching
stomach and back pain (severe)
unusual bleeding or bruising
vaginal irritation, discharge, or dryness not present before taking the medicine
Rare
Bleeding gums
dark urine
fast heartbeat
indigestion
loss of appetite
painful or difficult urination
pains in the stomach, side, or abdomen, possibly radiating to the back
sores, ulcers, or white spots on the lips or in the mouth
swollen glands
yellow eyes or skin
Incidence not known
Blistering, peeling, or loosening of the skin
bloody or cloudy urine
burning while urinating
continuing diarrhea
continuing stomach pain
feeling of warmth
increased volume of pale, dilute urine
joint or muscle pain
loss of bladder control
red skin lesions, often with a purple center
red, irritated eyes
redness of the face, neck, arms, and occasionally, upper chest
redness of the skin
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
More common
Dizziness or lightheadedness
feeling of constant movement of self or surroundings
sensation of spinning
stomach cramps
trouble sleeping
Rare
Change in taste sensation
congestion
pain or tenderness around the eyes and cheekbones
tender, swollen glands in the neck
trouble with swallowing
unpleasant or sharp metallic taste
voice changes
Incidence not known
Decreased interest in sexual intercourse
inability to have or keep an erection
loss in sexual ability, desire, drive, or performance
painful sexual intercourse
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
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Pros and cons of Metronidazole (Flagyl)
Pros
- Taken by mouth
- Available as a lower-cost generic medication
- Can be used to treat different types of bacterial infection
- Immediate-release formulations can be taken with or without food
Cons
- Immediate-release formulations needs to be taken multiple times a day for most infections
- Serious interaction with alcohol
- Can cause metallic taste in mouth
- Not recommended while breastfeeding
Pharmacist tips for Metronidazole (Flagyl)
- Don't drink alcohol or eat large amounts of food containing ethanol or propylene glycol while taking metronidazole (Flagyl) and for at least 3 days after. Doing so might cause belly cramps, nausea, vomiting, headaches, and flushing.
- Metronidazole (Flagyl) might get into breastmilk. If you're nursing, you might want to consider feeding your baby previously stored breast milk or infant formula while taking metronidazole (Flagyl) and for 2 days after treatment ends.
- If you're taking metronidazole (Flagyl) for trich, make sure that your sexual partner(s) also get treated to avoid getting reinfected. Don't have sex until you or your sexual partner(s) have finished treatment and have no more symptoms.
- Your primary care provider might also test you for human immunodeficiency virus (HIV) and other STIs if you tested positive for bacterial vaginosis (BV) or trich. Having BV or trich can raise your risk for other STIs as well.
- Metronidazole (Flagyl) can interact with many medications. Let your care team know what medications you're taking, including over-the-counter products and supplements, before you start metronidazole (Flagyl). Talk with your care team if you have any questions about interactions with this medication.
- Let your primary care provider know if you're taking blood thinners, like warfarin (Coumadin), before starting treatment. Metronidazole (Flagyl) can raise your risk of bleeding when taking these medications together.
More tips for the metronidazole (Flagyl) extended-release (ER) tablets
- Don't chew the metronidazole (Flagyl) extended-release (ER) tablets because doing so can alter how the medication gets absorbed into your body.
- Metronidazole (Flagyl) ER tablets should be taken on an empty stomach, an hour before or 2 hours after your meals.
More on Metronidazole (Flagyl) tips
Risks and warnings for Metronidazole (Flagyl)
Metronidazole (Flagyl) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.
Possible risk of cancer
- Risk factor: Taking metronidazole (Flagyl) for a long time
It’s not clear whether or not taking metronidazole (Flagyl) can put you at risk for cancer. Studies show that rats who took this medication throughout their lifetime were at higher risk for tumors in the liver, lung, and different organs. If you're taking metronidazole (Flagyl), don't take this medication more often than what your primary care provider has directed.
Serious allergic reactions
Metronidazole (Flagyl) can sometimes cause rash and other severe skin reactions, such as Stevens-Johnson syndrome (SJS). If you experience these reactions, your care team will need to stop metronidazole (Flagyl) right away and switch you to a different medication. If you've a rash, blisters on your lips, skin peeling, skin pain, mouth sores, or high fever, get medical help immediately.
Brain and nerve problems
Rarely, people who take metronidazole (Flagyl) can develop serious brain and nerve problems, such as seizures, encephalopathy (a health condition that leads to brain damage) or meningitis (inflammation of the brain lining). Get medical attention right away if you experience convulsions, problems with speech, coordination, clear thinking, headache, nausea, vomiting, stiff neck, and sensitivity to light. These are symptoms of brain damage and your care team might ask you to stop taking metronidazole (Flagyl) to prevent further injury. Symptoms can develop within hours of treatment, but will also go away within days to weeks of stopping this medication.
In addition, people who take metronidazole (Flagyl) might also experience different nerve problems. Let your primary care provider know if you experience numbness in the hands and feet, pain when moving the eye, or changes in vision. Your primary care provider will discuss with you whether metronidazole (Flagyl) is a good option for you.
Liver and kidney problems
- Risk factors: Current or history of liver problems | Current or history of kidney problems
People with liver or kidney problems who take metronidazole (Flagyl) might have a higher amount of the medication in the blood. This can lead to higher risk of side effects, such as nausea, headache, and seizures. Depending on how severe your liver or kidney problems are, your care team will help you determine the lowest possible dose of metronidazole (Flagyl) that is safe for you. If you experience symptoms of liver problems (feeling sleepy, upper right stomach pain, yellowing of the skin or eyes, dark urine) or kidney problems (urinating more or less than usual, feel nauseous or weak, have a fever, rash, joint pain), talk with your care team right away.
Risk of fungal infection
Taking metronidazole (Flagyl) can raise your risk of getting a fungal infection, including a vaginal yeast infection. It's important to let your care team know if your symptoms don't go away or get worse after starting treatment. Your primary care provider might prescribe an antifungal medication for you if symptoms develop. Please talk with your care team if you notice your vagina is red and itchy, you have thick white vaginal fluid, or if you've fever or chills.
Risk of drug resistance
- Risk factors: Taking metronidazole (Flagyl) more often or differently than prescribed
Taking metronidazole (Flagyl) more often or differently than prescribed can put you at risk for infections that are harder to treat in the future. To make sure that this medication will work well to fight future infections, follow your care team's instructions on when and how long to take metronidazole (Flagyl).
Lower white blood cell counts
- Risk factors: Current or history of blood problems | Taking medications that lower white blood cell counts
Though extremely rare, some people developed lower white blood cell count while taking metronidazole (Flagyl). This can put you at higher risk for infections. Your primary care provider will typically require lab work before and while you're taking this medication to make sure it's safe for you. Let your care team know if you've symptoms of low white blood cells, such as fever, chills, weakness, fast heart beat, sores in the mouth and throat.
Interaction with other medications
Metronidazole (Flagyl) can interfere with how your body gets rid of other medications. For example, taking certain medications like disulfiram with metronidazole (Flagyl) can cause delusions and hallucinations. These medications should be avoided together.
When metronidazole (Flagyl) is taken with lithium, it can raise the amount of lithium in your body. This can lead to higher risk of lithium toxicity and side effects, such as confusion, tremors, and uncontrolled eye movements.
Metronidazole (Flagyl) can also raise the risk of bleeding when it's taken with certain blood thinners, such as warfarin (Coumadin). Make sure to get your routine blood tests done on time during treatment.
Let your care team know what other medications you’re taking before and while taking metronidazole (Flagyl).
Metronidazole (Flagyl) dosage
The average cost for 14 tablets of 500mg of Metronidazole (Flagyl) is $10.73 with a free GoodRx coupon. This is 32.00% off the average retail price of $15.78.
Typical dosage for Metronidazole (Flagyl)
The typical dosing for metronidazole (Flagyl) can differ for each person depending on what type of infection you have. Your dose might also differ if you have kidney or liver problems.
Adults
- Trichomoniasis (1-day course): The typical dosing is 2 grams by mouth, taken as a single dose or split into 2 doses and taken in one day.
- Trichomoniasis (7-day course): The typical dosing is 250 mg by mouth 3 times daily for a week.
- Amebiasis: The typical dosing ranges from 500 mg to 750 mg by mouth 3 times daily for 5-10 days.
- Bacterial infections: Dosing for certain bacterial infections will depend on your weight and the severity of the infection. The typical dosing is 7.5 mg/kg of body weight by mouth every 6 hours for 7 to 10 days. The maximum recommended dose is 4 grams daily.
- Trichomoniasis: The typical dosing is 375 mg by mouth 2 times daily for a week.
- Amebiasis: The typical dosing is 750 mg by mouth 3 times daily for 5-10 days.
- Bacterial infections: Dosing for certain bacterial infections will depend on your weight and the severity of the infection. The typical dosing is 7.5 mg/kg of body weight by mouth every 6 hours for 7 to 10 days. The maximum recommended dose is 4 grams daily.
- Bacterial vaginosis: The typical dosing is 750 mg by mouth once a day for a week.
Children
IR tablets and capsules
- Amebiasis: Your child's pediatrician will determine the dose based on your child's body weight. The typical dose is 35 mg/kg to 50 mg/kg of body weight by mouth daily, split into 3 doses and taken throughout the day for 10 days.
More on Metronidazole (Flagyl) dosage
Interactions between Metronidazole (Flagyl) and other drugs
Metronidazole (Flagyl) may interact with certain medications or supplements. Always let your doctor and pharmacist know about any other medications or supplements (including prescribed and over-the-counter medications, vitamins, and dietary or herbal supplements) that you are currently taking. The list below does not include all possible drug interactions with Metronidazole (Flagyl). Please note that only the generic name of each medication is listed below.
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Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
- Amprenavir
- Bepridil
- Cisapride
- Disulfiram
- Dronabinol
- Dronedarone
- Mesoridazine
- Pimozide
- Saquinavir
- Sparfloxacin
- Terfenadine
- Thioridazine
- Ziprasidone
Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Alfuzosin
- Amiodarone
- Amitriptyline
- Anagrelide
- Apomorphine
- Aripiprazole
- Aripiprazole Lauroxil
- Arsenic Trioxide
- Asenapine
- Astemizole
- Atazanavir
- Azithromycin
- Bedaquiline
- Buprenorphine
- Bupropion
- Buserelin
- Busulfan
- Capecitabine
- Ceritinib
- Chloroquine
- Chlorpromazine
- Cholera Vaccine, Live
- Ciprofloxacin
- Citalopram
- Clarithromycin
- Clofazimine
- Clomipramine
- Clozapine
- Crizotinib
- Cyclobenzaprine
- Dabrafenib
- Dasatinib
- Degarelix
- Delamanid
- Desipramine
- Deslorelin
- Deutetrabenazine
- Disopyramide
- Dofetilide
- Dolasetron
- Domperidone
- Donepezil
- Doxepin
- Doxifluridine
- Droperidol
- Ebastine
- Efavirenz
- Encorafenib
- Entrectinib
- Eribulin
- Erythromycin
- Escitalopram
- Famotidine
- Felbamate
- Fingolimod
- Flecainide
- Fluconazole
- Fluorouracil
- Fluoxetine
- Formoterol
- Foscarnet
- Fosphenytoin
- Galantamine
- Gatifloxacin
- Gemifloxacin
- Glasdegib
- Gonadorelin
- Goserelin
- Granisetron
- Halofantrine
- Haloperidol
- Histrelin
- Hydroquinidine
- Hydroxychloroquine
- Hydroxyzine
- Ibutilide
- Iloperidone
- Imipramine
- Inotuzumab Ozogamicin
- Itraconazole
- Ivabradine
- Ivosidenib
- Ketoconazole
- Lapatinib
- Levofloxacin
- Lofexidine
- Lumefantrine
- Macimorelin
- Mebendazole
- Mefloquine
- Methadone
- Mifepristone
- Mizolastine
- Moxifloxacin
- Mycophenolate Mofetil
- Mycophenolic Acid
- Nafarelin
- Nelfinavir
- Nilotinib
- Norfloxacin
- Octreotide
- Ofloxacin
- Olanzapine
- Ondansetron
- Osimertinib
- Oxaliplatin
- Ozanimod
- Paliperidone
- Panobinostat
- Papaverine Hydrochloride
- Paroxetine
- Pasireotide
- Pazopanib
- Pentamidine
- Perphenazine
- Pimavanserin
- Pipamperone
- Pitolisant
- Ponesimod
- Posaconazole
- Probucol
- Procainamide
- Prochlorperazine
- Promethazine
- Propafenone
- Protriptyline
- Quetiapine
- Quinidine
- Quinine
- Ranolazine
- Ribociclib
- Risperidone
- Ritonavir
- Selpercatinib
- Sertindole
- Sertraline
- Sevoflurane
- Siponimod
- Sodium Phosphate
- Sodium Phosphate, Dibasic
- Sodium Phosphate, Monobasic
- Solifenacin
- Sorafenib
- Sotalol
- Sulpiride
- Sunitinib
- Tacrolimus
- Tamoxifen
- Tegafur
- Telaprevir
- Telavancin
- Telithromycin
- Tetrabenazine
- Tolterodine
- Toremifene
- Trazodone
- Trimipramine
- Triptorelin
- Vandetanib
- Vardenafil
- Vemurafenib
- Venlafaxine
- Vilanterol
- Vinflunine
- Voclosporin
- Voriconazole
- Vorinostat
- Warfarin
- Zuclopenthixol
Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Carbamazepine
- Cholestyramine
- Cyclosporine
- Lithium
- Milk Thistle
How much does Metronidazole (Flagyl) cost?
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Metronidazole (Flagyl) contraindications
Contraindications are specific health conditions or situations in which a person should not take a medication due to safety concerns. If you have any of the following conditions or if any of the following apply to you, let your healthcare provider know because Metronidazole (Flagyl) will not be safe for you to take.
- Trichomoniasis during first trimester of pregnancy
- Taking disulfiram in the last two weeks
- Drinking alcohol
- Cockayne syndrome, which can lead to liver problems
What are alternatives to Metronidazole (Flagyl)?
There are a number of medications that your doctor can prescribe in place of Metronidazole (Flagyl). Compare a few possible alternatives below.
Metronidazole (Flagyl)
Used for:
Treatment of certain bacterial and parasitic infections, including:
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Metronidazole (Flagyl) images
