Metronidazole 500mg Tablets
WARNING: Metronidazole has been shown to cause cancer in mice and rats with long-term use. Talk with the doctor.The doctor has given you this drug for a certain health problem. Do not use this drug for other health problems. @ COMMON USES: It is used to treat infections.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Antibiotic, Antiprotozoal
Pharmacologic Class
Nitroimidazole
Pregnancy Category
Category B (older classification, refer to current labeling for risk summary)
FDA Approved
Sep 1963
DEA Schedule
Not Controlled
Overview
What is this medicine?
Metronidazole is an antibiotic that fights certain types of bacteria and parasites. It's used to treat various infections, including those of the reproductive organs, gastrointestinal tract, skin, joints, and respiratory tract.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. If you experience stomach upset, taking it with food may help. Continue taking your medication as prescribed by your doctor or healthcare provider, even if you're feeling well.
Storing and Disposing of Your Medication
Store your medication at room temperature, protected from light, and in a dry place. Avoid storing it in a bathroom. Keep all medications in a safe location, out of the reach of children and pets. Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so. If you're unsure about the best way to dispose of your medication, consult your pharmacist. You may also want to check if there are drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. If you experience stomach upset, taking it with food may help. Continue taking your medication as prescribed by your doctor or healthcare provider, even if you're feeling well.
Storing and Disposing of Your Medication
Store your medication at room temperature, protected from light, and in a dry place. Avoid storing it in a bathroom. Keep all medications in a safe location, out of the reach of children and pets. Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so. If you're unsure about the best way to dispose of your medication, consult your pharmacist. You may also want to check if there are drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
Lifestyle & Tips
- Avoid all alcohol (including alcohol-containing medications, mouthwash, hand sanitizers, and food products) during treatment and for at least 3 days after stopping metronidazole, due to a severe disulfiram-like reaction (nausea, vomiting, flushing, headache, abdominal cramps).
- Take with food or milk if stomach upset occurs.
- Complete the full course of medication, even if symptoms improve, to prevent recurrence and antibiotic resistance.
- May cause a metallic taste in the mouth.
- Urine may turn dark or reddish-brown, which is a harmless side effect.
Available Forms & Alternatives
Available Strengths:
- Metronidazole 0.75% Topical Crm 45g
- Metronidazole 250mg Tablets
- Metronidazole 0.75% Topical Lotion
- Metron/nacl 500mg Pb Inj, 100ml
- Metronidazole 0.75% Vaginal Gel 70g
- Metronidazole 500mg Tablets
- Metronidazole 0.75% Topical Crm 45g
- Metronidazole 0.75% Topical Gel 45g
- Metronidazole 375mg Capsules
- Metronidazole 500mg Tablets
- Metronidazole 250mg Tablets
- Metronidazole 1% Topical Gel Pump
- Metronidazole 1% Topical Gel Tube
- Metronidazole 500mg/100ml Inj,100ml
- Metronidazole 0.75% Vaginal Gel 70g
Dosing & Administration
Adult Dosing
Standard Dose:
Varies by indication. E.g., 500 mg orally every 8 hours for 7-10 days for anaerobic bacterial infections; 500 mg orally twice daily for 7 days for bacterial vaginosis; 2 grams orally as a single dose or 500 mg orally twice daily for 7 days for trichomoniasis.
Dose Range:
250 - 2000 mg
Condition-Specific Dosing:
Anaerobic Infections:
500 mg every 8 hours for 7-10 days
Trichomoniasis:
2 g single dose or 500 mg BID for 7 days
Bacterial Vaginosis:
500 mg BID for 7 days
Clostridioides difficile infection (CDI):
500 mg orally three times daily for 10-14 days (for mild-moderate cases or as adjunct)
Pediatric Dosing
Neonatal:
Not established for routine use; specific dosing for certain infections (e.g., necrotizing enterocolitis) under specialist guidance.
Infant:
Dosing exists for specific infections (e.g., amebiasis, giardiasis, anaerobic infections) based on weight (e.g., 15-30 mg/kg/day divided every 8 hours).
Child:
Dosing exists for specific infections (e.g., 15-35 mg/kg/day divided every 8 hours, max 4 g/day).
Adolescent:
Typically adult dosing for most indications.
Dose Adjustments
Renal Impairment:
Mild:
No adjustment needed
Moderate:
No adjustment needed
Severe:
No adjustment needed, but caution with accumulation of metabolites in ESRD. Monitor for adverse effects.
Dialysis:
Hemodialysis removes metronidazole and its metabolites. Administer dose after dialysis on dialysis days. Peritoneal dialysis does not significantly remove metronidazole.
Hepatic Impairment:
Mild:
No adjustment
Moderate:
Reduce dose by 50% for patients with severe hepatic impairment (Child-Pugh C).
Severe:
Reduce dose by 50% for patients with severe hepatic impairment (Child-Pugh C). Monitor plasma levels if possible.
Pharmacology
Mechanism of Action
Metronidazole is a nitroimidazole antimicrobial. It enters the cell of anaerobic bacteria and sensitive protozoa, where its nitro group is reduced by electron transport proteins to highly reactive nitro radical anions. These reactive intermediates disrupt DNA synthesis and cause DNA damage, leading to cell death.
Pharmacokinetics
Absorption:
Bioavailability:
Approximately 100%
Tmax:
1-2 hours
FoodEffect:
Food delays Tmax but does not significantly affect the extent of absorption (AUC). Taking with food may reduce GI upset.
Distribution:
Vd:
0.51-1.1 L/kg
ProteinBinding:
<20%
CnssPenetration:
Yes (achieves therapeutic concentrations in CSF, brain abscesses)
Elimination:
HalfLife:
6-11 hours (parent drug), 9.5-18 hours (hydroxymetabolite)
Clearance:
Not readily available as a single value, varies with hepatic function.
ExcretionRoute:
Renal (60-80%), Fecal (6-15%)
Unchanged:
Approximately 20% (renal)
Pharmacodynamics
OnsetOfAction:
Rapid (within hours for susceptible organisms)
PeakEffect:
Within 1-3 hours post-dose
DurationOfAction:
Dependent on half-life and dosing interval (typically maintains therapeutic levels for 8-12 hours)
Confidence:
Medium
Safety & Warnings
BLACK BOX WARNING
Metronidazole has been shown to be carcinogenic in mice and rats. Tumors of the lung and liver have been observed in mice and tumors of the mammary and liver have been observed in rats. These findings have been observed in studies with chronic (lifetime) exposure to metronidazole. Although these studies have been conducted at doses higher than the usual human dose, the clinical significance of these findings is unknown. Therefore, metronidazole should be used only when clearly necessary.
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience any of the following symptoms, contact your doctor immediately or seek emergency medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Redness or white patches in the mouth or throat
Vaginal itching or discharge
Fast or abnormal heartbeat
Pain when passing urine or blood in urine
Passing urine more often
Pelvic pain
Ringing in the ears, hearing loss, or any other changes in hearing
Nervous System Problems
This medication can cause nervous system problems, which can be long-lasting. If you experience any of the following symptoms, contact your doctor right away:
Burning, numbness, or tingling sensations that are not normal
Changes in balance or eyesight
Dizziness or fainting
Headache
Difficulty sleeping
Seizures
Trouble speaking
Confusion
Depression
Irritability
Fatigue
Weakness
Aseptic Meningitis
This medication may increase the risk of a severe brain problem called aseptic meningitis. If you experience any of the following symptoms, contact your doctor right away:
Headache
Fever
Chills
Severe stomach upset or vomiting
Stiff neck
Rash
Sensitivity to light
Feeling sleepy or confused
Low White Blood Cell Count
This medication can cause a low white blood cell count, which can increase the risk of infection. If you experience any of the following symptoms, contact your doctor right away:
Fever
Chills
Sore throat
Severe Skin Reactions
This medication can cause severe skin reactions, including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and other serious reactions. If you experience any of the following symptoms, seek medical help right away:
Red, swollen, blistered, or peeling skin
Red or irritated eyes
Sores in the mouth, throat, nose, eyes, genitals, or any areas of skin
Fever
Chills
Body aches
Shortness of breath
Swollen glands
Other Side Effects
Most people do not experience side effects or only have minor side effects. However, if you experience any of the following side effects, contact your doctor or seek medical help if they bother you or do not go away:
Constipation
Diarrhea
Stomach pain
Upset stomach
Vomiting
Decreased appetite
Stomach cramps
Metallic taste
Headache
Joint pain
Decreased interest in sex
Reporting Side Effects
If you have questions about side effects or want to report a side effect, contact your doctor or call the FDA at 1-800-332-1088. You can also report side effects online at https://www.fda.gov/medwatch.
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience any of the following symptoms, contact your doctor immediately or seek emergency medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Redness or white patches in the mouth or throat
Vaginal itching or discharge
Fast or abnormal heartbeat
Pain when passing urine or blood in urine
Passing urine more often
Pelvic pain
Ringing in the ears, hearing loss, or any other changes in hearing
Nervous System Problems
This medication can cause nervous system problems, which can be long-lasting. If you experience any of the following symptoms, contact your doctor right away:
Burning, numbness, or tingling sensations that are not normal
Changes in balance or eyesight
Dizziness or fainting
Headache
Difficulty sleeping
Seizures
Trouble speaking
Confusion
Depression
Irritability
Fatigue
Weakness
Aseptic Meningitis
This medication may increase the risk of a severe brain problem called aseptic meningitis. If you experience any of the following symptoms, contact your doctor right away:
Headache
Fever
Chills
Severe stomach upset or vomiting
Stiff neck
Rash
Sensitivity to light
Feeling sleepy or confused
Low White Blood Cell Count
This medication can cause a low white blood cell count, which can increase the risk of infection. If you experience any of the following symptoms, contact your doctor right away:
Fever
Chills
Sore throat
Severe Skin Reactions
This medication can cause severe skin reactions, including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and other serious reactions. If you experience any of the following symptoms, seek medical help right away:
Red, swollen, blistered, or peeling skin
Red or irritated eyes
Sores in the mouth, throat, nose, eyes, genitals, or any areas of skin
Fever
Chills
Body aches
Shortness of breath
Swollen glands
Other Side Effects
Most people do not experience side effects or only have minor side effects. However, if you experience any of the following side effects, contact your doctor or seek medical help if they bother you or do not go away:
Constipation
Diarrhea
Stomach pain
Upset stomach
Vomiting
Decreased appetite
Stomach cramps
Metallic taste
Headache
Joint pain
Decreased interest in sex
Reporting Side Effects
If you have questions about side effects or want to report a side effect, contact your doctor or call the FDA at 1-800-332-1088. You can also report side effects online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe allergic reaction (rash, itching/swelling, severe dizziness, trouble breathing)
- Signs of nerve damage (numbness, tingling, pain, or weakness in hands or feet)
- Seizures
- Severe headache, stiff neck, confusion, fever (signs of aseptic meningitis)
- Vision changes (e.g., double vision, blurred vision)
- Dizziness or lightheadedness
- Severe diarrhea (especially if watery or bloody, may indicate C. difficile infection)
- Unusual bruising or bleeding
- Signs of liver problems (yellowing eyes/skin, dark urine, severe stomach pain, persistent nausea/vomiting)
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you have Cockayne syndrome, as some individuals with this condition have developed liver problems while taking this medication. In some cases, these liver problems have been severe, persistent, or even fatal.
If you have taken disulfiram within the past 14 days.
If you are less than 12 weeks pregnant, as this medication is not intended for use in certain patients during this stage of pregnancy.
This list is not exhaustive, and it is crucial to discuss all your medications (prescription, over-the-counter, natural products, and vitamins) and health issues with your doctor and pharmacist. They will help determine whether it is safe to take this medication in conjunction with your other treatments and health conditions. Never start, stop, or adjust the dosage of any medication without first consulting your doctor.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
If you have Cockayne syndrome, as some individuals with this condition have developed liver problems while taking this medication. In some cases, these liver problems have been severe, persistent, or even fatal.
If you have taken disulfiram within the past 14 days.
If you are less than 12 weeks pregnant, as this medication is not intended for use in certain patients during this stage of pregnancy.
This list is not exhaustive, and it is crucial to discuss all your medications (prescription, over-the-counter, natural products, and vitamins) and health issues with your doctor and pharmacist. They will help determine whether it is safe to take this medication in conjunction with your other treatments and health conditions. Never start, stop, or adjust the dosage of any medication without first consulting your doctor.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. Regular blood tests will be necessary, as directed by your doctor, and you should discuss the schedule and any concerns with them.
This medication may interfere with certain laboratory tests, so it is crucial to notify all your healthcare providers and laboratory personnel that you are taking this drug. If you are undergoing dialysis, consult with your doctor to discuss any necessary precautions.
To minimize potential interactions, you may need to avoid consuming alcohol and products containing alcohol or propylene glycol during treatment with this medication and for at least 72 hours after your last dose. Examples of products that may contain alcohol or propylene glycol include some cough syrups. Consuming these substances may cause adverse effects such as stomach cramps, nausea, vomiting, headaches, and flushing. Consult with your doctor to determine if you need to avoid these substances.
Do not exceed the recommended duration of treatment, as this may increase the risk of a secondary infection. If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, inform your doctor, as they will need to discuss the potential benefits and risks of this medication to both you and your baby.
This medication may interfere with certain laboratory tests, so it is crucial to notify all your healthcare providers and laboratory personnel that you are taking this drug. If you are undergoing dialysis, consult with your doctor to discuss any necessary precautions.
To minimize potential interactions, you may need to avoid consuming alcohol and products containing alcohol or propylene glycol during treatment with this medication and for at least 72 hours after your last dose. Examples of products that may contain alcohol or propylene glycol include some cough syrups. Consuming these substances may cause adverse effects such as stomach cramps, nausea, vomiting, headaches, and flushing. Consult with your doctor to determine if you need to avoid these substances.
Do not exceed the recommended duration of treatment, as this may increase the risk of a secondary infection. If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, inform your doctor, as they will need to discuss the potential benefits and risks of this medication to both you and your baby.
Overdose Information
Overdose Symptoms:
- Nausea
- Vomiting
- Ataxia (loss of coordination)
- Disorientation
- Seizures
- Peripheral neuropathy
What to Do:
There is no specific antidote for metronidazole overdose. Treatment is symptomatic and supportive. Contact a poison control center immediately (Call 1-800-222-1222 in the US).
Drug Interactions
Contraindicated Interactions
- Alcohol (disulfiram-like reaction)
- Disulfiram (psychotic reactions)
Major Interactions
- Warfarin (increased anticoagulant effect)
- Lithium (increased lithium levels, toxicity)
- Busulfan (increased busulfan levels, toxicity)
- Phenytoin (increased phenytoin levels, decreased metronidazole levels)
- Phenobarbital (decreased metronidazole levels)
Moderate Interactions
- Cimetidine (decreased metronidazole clearance)
- Fluorouracil (increased fluorouracil toxicity)
- Tacrolimus (increased tacrolimus levels)
- Cyclosporine (increased cyclosporine levels)
Minor Interactions
- Oral contraceptives (potential for reduced efficacy, though clinical significance debated)
Monitoring
Baseline Monitoring
Liver Function Tests (LFTs)
Rationale: To assess baseline hepatic function, especially in patients with known or suspected hepatic impairment, as metronidazole is primarily metabolized by the liver.
Timing: Prior to initiation in patients with hepatic impairment.
Complete Blood Count (CBC)
Rationale: To establish baseline hematologic status, particularly if prolonged therapy is anticipated, due to rare reports of neutropenia and leukopenia.
Timing: Prior to initiation for prolonged therapy.
Routine Monitoring
Neurological Assessment (e.g., signs of peripheral neuropathy, seizures, encephalopathy)
Frequency: Periodically, especially with prolonged or high-dose therapy
Target: Absence of new or worsening neurological symptoms
Action Threshold: Discontinue metronidazole immediately if signs of central nervous system toxicity (e.g., seizures, encephalopathy) or peripheral neuropathy (e.g., numbness, tingling) occur.
Liver Function Tests (LFTs)
Frequency: Periodically, especially in patients with hepatic impairment or prolonged therapy
Target: Within normal limits or stable
Action Threshold: Significant elevation may warrant dose adjustment or discontinuation.
Complete Blood Count (CBC)
Frequency: Periodically, especially with prolonged therapy (>10 days)
Target: WBC and neutrophil counts within normal limits
Action Threshold: Significant decrease in WBC or neutrophil count may warrant discontinuation.
Symptom Monitoring
- Nausea
- Vomiting
- Diarrhea
- Metallic taste
- Headache
- Dizziness
- Peripheral neuropathy (numbness, tingling, weakness)
- Seizures
- Encephalopathy
- Rash
- Darkening of urine
Special Patient Groups
Pregnancy
Metronidazole crosses the placenta. While older classifications listed it as Category B, current labeling advises use only if clearly needed, especially during the first trimester. For trichomoniasis, a single 2g dose is generally avoided in the first trimester unless other options are not feasible or the infection is severe. For other indications, the benefits should outweigh the potential risks.
Trimester-Specific Risks:
First Trimester:
Some studies suggest a possible association with congenital anomalies, but data are conflicting and largely reassuring. Generally avoided for trichomoniasis unless severe or no alternatives.
Second Trimester:
Generally considered safer than in the first trimester; often used for trichomoniasis.
Third Trimester:
Generally considered safer than in the first trimester; often used for trichomoniasis.
Lactation
Metronidazole is excreted into breast milk in concentrations similar to maternal plasma levels. The American Academy of Pediatrics (AAP) considers it compatible with breastfeeding, but some sources recommend temporary interruption of breastfeeding (e.g., for 12-24 hours) after a single high dose (e.g., 2g) to minimize infant exposure.
Infant Risk:
Low to moderate risk. Potential for infant GI upset (diarrhea, candidiasis), metallic taste, and theoretical concern for carcinogenicity (though risk is likely very low with short-term use). Monitor infant for adverse effects.
Pediatric Use
Dosing is weight-based and varies by indication. Safety and efficacy are established for various infections. Caution with prolonged use due to potential for neurotoxicity.
Geriatric Use
No specific dose adjustment is typically required based on age alone. However, elderly patients may have reduced hepatic or renal function, which could necessitate dose adjustments or increased monitoring for adverse effects, particularly neurological ones.
Clinical Information
Clinical Pearls
- Always counsel patients to avoid alcohol during and for at least 3 days after metronidazole therapy due to the severe disulfiram-like reaction.
- Metallic taste is a very common and expected side effect; reassure patients it is temporary.
- Darkening of urine is a harmless side effect.
- Monitor for neurological symptoms (e.g., numbness, tingling, seizures, encephalopathy) especially with high doses or prolonged therapy, as these can be serious and require discontinuation.
- Metronidazole is effective against anaerobic bacteria and certain protozoa, but not aerobic bacteria.
- For C. difficile infection, oral vancomycin or fidaxomicin are generally preferred for initial episodes, with metronidazole reserved for mild-moderate cases or as an alternative when first-line agents are not available/tolerated.
Alternative Therapies
- Clindamycin (for anaerobic infections, bacterial vaginosis)
- Tinidazole (another nitroimidazole, similar spectrum, longer half-life)
- Vancomycin (oral, for C. difficile infection)
- Fidaxomicin (for C. difficile infection)
- Secnidazole (single-dose treatment for bacterial vaginosis, trichomoniasis)
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (500mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it's essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so be sure to check with your pharmacist for more information. If you have any questions or concerns about your medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide details about the medication taken, the amount, and the time it happened.