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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Brand Name
Metronidazole
Generic Name
Metronidazole
Active Ingredient
MetronidazoleCategory
Nitroimidazole Antimicrobial [EPC]
Variants
152
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Metronidazole, you must consult a qualified healthcare professional.
| 500 mg/1 | TABLET | ORAL | 65862-695 |
| 500 mg/1 | TABLET, FILM COATED | ORAL | 67296-2152 |
| 250 mg/1 | TABLET | ORAL | 70518-0013 |
| 500 mg/1 | TABLET | ORAL | 70518-1241 |
| 500 mg/1 | TABLET | ORAL | 82982-072 |
| 250 mg/1 | TABLET | ORAL | 58657-933 |
| 500 mg/1 | TABLET | ORAL | 60687-550 |
| 250 mg/1 | TABLET | ORAL | 62332-016 |
| 500 mg/1 | TABLET, FILM COATED | ORAL | 63187-827 |
+ 38 more variants
Detailed information about Metronidazole
Metronidazole is a potent nitroimidazole antimicrobial used to treat a wide array of anaerobic bacterial and protozoal infections. It is a critical agent in treating conditions like amebiasis, trichomoniasis, and various surgical infections.
Dosage for metronidazole is highly individualized based on the type of infection and the patient's overall health. According to the FDA-approved labeling, typical adult regimens include:
Metronidazole is used in pediatric populations, though dosing is strictly weight-based.
Healthcare providers must carefully calculate these doses to ensure safety and efficacy in children. Always consult a pediatrician for specific instructions.
In patients with end-stage renal disease (ESRD), metronidazole and its metabolites can accumulate. While standard doses may be used for short courses, clinicians may monitor for toxicity. For patients on hemodialysis, metronidazole is rapidly removed; therefore, a supplemental dose may be administered immediately following the dialysis session.
Because metronidazole is primarily metabolized in the liver, patients with severe hepatic impairment (liver disease) process the drug slowly. This can lead to plasma accumulation and increased risk of adverse effects. In these cases, healthcare providers typically reduce the dose by 50% or increase the interval between doses.
Geriatric patients may have decreased hepatic or renal function. Clinicians often start at the lower end of the dosing range and monitor closely for neurological side effects, such as dizziness or confusion.
To ensure the medication works effectively and to minimize side effects, follow these guidelines:
If you miss a dose, take it as soon as you remember. However, if it is almost time for your next scheduled dose, skip the missed dose and resume your regular schedule. Do not double the dose to catch up, as this increases the risk of toxicity.
Signs of metronidazole overdose may include nausea, vomiting, ataxia (loss of muscle coordination), and slight disorientation. In severe cases, seizures or peripheral neuropathy may occur. If an overdose is suspected, contact a Poison Control Center or seek emergency medical attention immediately. Treatment is primarily supportive, as there is no specific antidote for metronidazole poisoning.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop the medication without medical guidance.
Many patients taking metronidazole experience mild to moderate side effects. The most frequently reported include:
Metronidazole is a powerful antimicrobial that requires careful monitoring. Patients must be aware of the risk of neurological toxicity and the potential for severe reactions when combined with certain substances. It is vital to disclose your full medical history, especially any history of blood disorders, liver disease, or neurological conditions, to your healthcare provider before starting treatment.
Metronidazole is associated with a risk of carcinogenicity. According to the FDA, metronidazole has been shown to be carcinogenic in mice and rats in experimental studies. Because of this, it should only be used for its approved indications. Patients should not use this medication for viral infections (like the common cold) or for any condition not specifically prescribed by a doctor. Healthcare providers aim to use the shortest effective course to minimize potential risks.
There are several scenarios where metronidazole must never be used due to the risk of life-threatening complications:
Metronidazole crosses the placental barrier. According to the FDA, it is classified in a way that suggests caution. While many studies and meta-analyses (including a large review by the CDC) have not shown a consistent link between metronidazole use and birth defects or miscarriage, its use during the first trimester for trichomoniasis is contraindicated. For other serious infections, healthcare providers weigh the risk of the untreated infection against the potential risk to the fetus. It should be used during pregnancy only if clearly needed and under strict medical supervision.
Metronidazole is excreted into human breast milk in concentrations similar to those found in the mother's blood. Because animal studies have shown a potential for carcinogenicity, many experts suggest a 'pump and discard' approach. If a mother must take a single large dose (e.g., 2 grams for trichomoniasis), it is often recommended to interrupt breastfeeding for 12 to 24 hours after the dose to allow the drug to clear from the milk. For longer courses, your doctor may recommend alternative feeding methods or a different antibiotic if possible.
Metronidazole is approved for use in children for specific conditions like amebiasis. However, its safety and effectiveness for other uses in pediatric patients have not been as extensively established. Pediatricians must carefully calculate doses based on weight (mg/kg). Long-term effects on growth and development have not been fully characterized, so use is typically limited to the shortest duration necessary.
Metronidazole is a member of the nitroimidazole class. Its action is dependent on the reduction of its nitro group by anaerobic organisms. In these pathogens, the drug acts as an electron sink, intercepting electrons from ferredoxin-linked metabolic pathways. This reduction creates a highly reactive nitro radical anion. This radical causes extensive damage to the microbial DNA by inducing strand breaks and inhibiting the DNA repair enzyme systems. This 'suicide' mechanism ensures that the drug is only toxic to organisms capable of reducing it, which primarily includes anaerobes and certain protozoa.
Metronidazole exhibits concentration-dependent killing, meaning that higher peak concentrations relative to the Minimum Inhibitory Concentration (MIC) of the pathogen lead to more effective eradication. It also possesses a significant post-antibiotic effect (PAE) against many anaerobes, meaning it continues to suppress bacterial growth even after the drug levels drop below the MIC. Resistance is relatively rare but can occur through the down-regulation of ferredoxin or the expression of 'nim' genes that detoxify the drug.
| Parameter | Value |
Common questions about Metronidazole
Metronidazole is a versatile antimicrobial medication primarily used to treat infections caused by anaerobic bacteria and certain parasites. Healthcare providers commonly prescribe it for conditions such as bacterial vaginosis, trichomoniasis, amebiasis, and giardiasis. It is also highly effective for serious internal infections, including intra-abdominal, pelvic, and bone infections where anaerobic bacteria are present. Additionally, it is used as part of a combination therapy to eradicate Helicobacter pylori, the bacterium responsible for many stomach ulcers. Because it specifically targets organisms that do not require oxygen, it is a critical tool in modern medicine for treating complex infections.
The most frequently reported side effects of metronidazole include a persistent metallic taste in the mouth, nausea, and stomach upset. Many patients also notice that their urine turns a darker, reddish-brown color, which is a harmless result of the drug being processed by the body. Other common issues include headaches, loss of appetite, and occasional dizziness or diarrhea. While these are usually mild and disappear after the treatment ends, they can be bothersome. If these side effects become severe or if you experience persistent vomiting, you should contact your healthcare provider for guidance on managing the symptoms.
No, you must strictly avoid alcohol while taking metronidazole and for at least 72 hours (three days) after your last dose. Combining alcohol with this medication triggers a disulfiram-like reaction, which can be extremely unpleasant and potentially dangerous. Symptoms of this reaction include severe nausea, projectile vomiting, abdominal cramps, rapid heartbeat, and intense flushing of the face and neck. This interaction occurs because metronidazole prevents the body from breaking down acetaldehyde, a toxic byproduct of alcohol. To stay safe, always check the labels of other medicines, such as cough syrups or mouthwashes, to ensure they do not contain alcohol or propylene glycol.
The safety of metronidazole during pregnancy depends on the trimester and the condition being treated. While many large-scale studies have not found a definitive link between metronidazole and birth defects, the FDA contraindicates its use during the first trimester for the treatment of trichomoniasis. For other serious bacterial infections, healthcare providers may decide that the benefits of treating the mother outweigh the potential risks to the fetus. If you are pregnant or planning to become pregnant, it is essential to discuss the necessity of this medication with your doctor. They will evaluate your specific situation and may recommend alternative antibiotics if appropriate for your stage of pregnancy.
Most patients begin to feel an improvement in their symptoms within 24 to 48 hours of starting metronidazole. However, the exact time frame depends on the type and severity of the infection being treated. For example, symptoms of bacterial vaginosis may improve quickly, while a deep-seated liver abscess may take longer to respond. Even if you feel completely better after just a few doses, it is vital to finish the entire course of medication as prescribed. Stopping the antibiotic early can allow the remaining bacteria or parasites to multiply, leading to a relapse of the infection and increasing the risk of antimicrobial resistance.
You should not stop taking metronidazole suddenly unless you are experiencing a severe allergic reaction or serious neurological side effects. While metronidazole does not cause physical withdrawal symptoms like some other medications, stopping an antibiotic early is dangerous for your health. If the full course is not completed, the toughest bacteria may survive and cause the infection to return, often in a more severe form. Furthermore, incomplete treatment contributes to the global problem of antibiotic resistance, making future infections harder to treat. Always consult your healthcare provider before deciding to discontinue your medication prematurely.
If you miss a dose of metronidazole, you should take it as soon as you realize you have forgotten. However, if it is nearly time for your next scheduled dose, you should skip the missed one and continue with your regular dosing schedule. It is important never to take two doses at once to make up for a missed one, as this can increase the concentration of the drug in your system and lead to a higher risk of side effects like nausea or dizziness. To help you remember, try using a pill organizer or setting a daily alarm on your phone to ensure you maintain consistent levels of the medication in your body.
Weight gain is not a recognized or common side effect of metronidazole. In fact, many patients report a temporary loss of appetite or slight weight loss due to side effects like nausea and the unpleasant metallic taste the drug can cause. If you notice significant or rapid weight gain while taking this medication, it is unlikely to be caused directly by the metronidazole and may be related to another underlying condition or a different medication you are taking. You should discuss any unexpected changes in your weight with your healthcare provider to determine the cause and ensure your treatment plan remains appropriate.
Metronidazole can interact with several other medications, so it is crucial to provide your doctor with a complete list of everything you are taking. Significant interactions occur with blood thinners like warfarin, which can increase your risk of bleeding, and lithium, which can lead to toxic levels of lithium in your blood. It also interacts with certain anti-seizure medications like phenytoin and phenobarbital. Because of these potential complications, your doctor may need to adjust your dosages or perform more frequent blood tests. Always consult a pharmacist or physician before starting any new over-the-counter drugs or supplements while on metronidazole.
Yes, metronidazole is widely available as a generic medication and is typically very affordable. The generic version is bioequivalent to the original brand-name drug, Flagyl, meaning it contains the same active ingredient and works in the same way within the body. Generic metronidazole is available in various forms, including oral tablets, capsules, and topical gels. Because it is a well-established medication that has been off-patent for many years, most insurance plans cover it as a 'Tier 1' or low-cost drug. Choosing the generic version is an effective way to receive high-quality treatment for anaerobic infections without the higher cost of a brand-name product.
Other drugs with the same active ingredient (Metronidazole)
> Warning: Stop taking Metronidazole and call your doctor immediately if you experience any of these serious symptoms:
Metronidazole is generally intended for short-term use (usually 7 to 14 days). Prolonged or repeated use can lead to:
Historically, metronidazole carried a black box warning regarding its carcinogenic potential in mice and rats. While the 'Boxed Warning' format has changed in newer labeling, the core warning remains: Metronidazole has been shown to be carcinogenic in mice and rats. Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the indications section. This highlights the importance of using this antibiotic only when a bacterial or parasitic infection is confirmed or strongly suspected.
Report any unusual symptoms to your healthcare provider immediately to ensure your safety throughout the treatment course.
For most short-term users, routine lab tests are not required. However, for those on prolonged therapy or with underlying health issues, healthcare providers may order:
Metronidazole may cause dizziness, confusion, hallucinations, or even seizures in some patients. You should not drive, operate heavy machinery, or engage in hazardous activities until you know how this medication affects you. If you feel lightheaded or confused, avoid these tasks and consult your healthcare provider.
Strict Avoidance of Alcohol is Required. Consuming alcohol while taking metronidazole, and for at least three days after the last dose, can cause a 'disulfiram-like reaction.' This is a severe chemical reaction characterized by abdominal cramps, nausea, vomiting, headaches, and flushing (redness of the face). This also applies to products containing propylene glycol (found in some liquid medications).
There is no specific tapering requirement for metronidazole, as it does not cause a physical withdrawal syndrome. However, stopping the medication too early can lead to 'treatment failure' or the development of antibiotic-resistant bacteria. Always finish the full course as prescribed by your doctor.
> Important: Discuss all your medical conditions with your healthcare provider before starting Metronidazole to ensure it is the safest choice for you.
Metronidazole can interfere with certain chemical analyses of serum chemistry, such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), triglycerides, and glucose hexokinase. It may cause these values to appear falsely low (specifically when using methods that involve a decrease in ultraviolet absorbance at 340 nm). Always inform the laboratory staff that you are taking metronidazole if you are undergoing blood tests.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking. A comprehensive review of your current regimen is the best way to prevent dangerous drug interactions.
In these conditions, a healthcare provider will perform a careful risk-benefit analysis:
Patients who have had an adverse reaction to other nitroimidazoles, such as tinidazole or secnidazole, are highly likely to react to metronidazole. Cross-sensitivity is common within this chemical class, and these patients should generally avoid all drugs in the nitroimidazole category.
> Important: Your healthcare provider will evaluate your complete medical history, including any rare genetic conditions or previous drug allergies, before prescribing Metronidazole.
Older adults are more susceptible to the side effects of metronidazole, particularly the neurological effects like confusion or dizziness. Because kidney and liver function naturally decline with age, the drug may stay in the body longer. Clinical studies have shown that the half-life of the drug can be prolonged in the elderly. Healthcare providers often start with lower doses and monitor liver function more frequently in this population.
In patients with a reduced Glomerular Filtration Rate (GFR), the parent drug is still cleared relatively well, but its metabolites can accumulate. For patients with severe renal failure (GFR < 10 mL/min), monitoring for toxicity is essential. For those on hemodialysis, the drug is removed quickly (half-life drops to about 3 hours), so doses are typically timed to be given after the dialysis session.
Patients with significant liver disease (e.g., Child-Pugh Class C) have a significantly reduced clearance of metronidazole. This can lead to toxic plasma levels. In these patients, the total daily dose is often reduced by 50% or more. Frequent monitoring of plasma levels, if available, or close clinical observation for neurological side effects is mandatory.
> Important: Special populations require individualized medical assessment to ensure that the benefits of metronidazole therapy outweigh the potential risks.
|---|---|
| Bioavailability | ~100% (Oral) |
| Protein Binding | <20% |
| Half-life | 8 hours (Adults) |
| Tmax | 1-2 hours |
| Metabolism | Hepatic (Oxidation/Glucuronidation) |
| Excretion | Renal (60-80%), Fecal (6-15%) |
The molecular formula for metronidazole is $C_6H_9N_3O_3$. It has a molecular weight of 171.15 g/mol. Chemically, it is 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol. It appears as a white to pale yellow crystalline powder and is sparingly soluble in water and alcohol. Its structure features a nitro group at the 5-position of the imidazole ring, which is the key to its antimicrobial activity.
Metronidazole is the prototype of the Nitroimidazole Antimicrobial class. Related medications include Tinidazole and Secnidazole. While these drugs share a similar mechanism, they differ in their half-lives and specific FDA-approved indications.