Metro (Metronidazole) Extended-Release Tablets

Metro is our catalog name for oral metronidazole extended-release tablets, supplied in 200 mg and 400 mg strengths. Metronidazole is a nitroimidazole antimicrobial that has been used for decades against susceptible anaerobic bacteria and certain protozoal organisms. This article explains what the active ingredient does, how extended-release tablets are generally used, what safety information matters most, and how Metro compares with related antibiotics and generic metronidazole so you can understand the medicine before you order.

What Is Metro (Metronidazole)?

Metro's active ingredient, metronidazole, belongs to the nitroimidazole class of antimicrobials (ATC code P01AB01). Unlike penicillins or cephalosporins, which interfere with bacterial cell-wall construction, metronidazole is activated inside susceptible microorganisms. The extended-release tablet is designed to release the medicine gradually after swallowing. The resulting dosing schedule depends on the specific product instructions, diagnosis, and prescribed regimen; extended-release tablets are not automatically interchangeable with immediate-release metronidazole. Metro should be swallowed whole and not chewed or crushed, because damaging an extended-release tablet can alter how the drug is released.

Infections Metronidazole Is Used to Treat

At the active-ingredient level, metronidazole's anaerobic and antiprotozoal activity makes it useful for several distinct conditions. These include certain anaerobic bacterial infections involving the abdomen, pelvis, skin, or bone; bacterial vaginosis, which is associated with an imbalance of vaginal bacteria; and protozoal infections such as trichomoniasis, giardiasis, and amebiasis. Not every dosage form, strength, or regimen is suitable for every metronidazole-responsive infection. Readers researching this medicine for gynecologic reasons may also find it useful to review our Woman's Health section for related treatment options. Metronidazole may also be combined with other medicines, including amoxicillin, in some multidrug regimens used to eradicate Helicobacter pylori; our Polymox listing covers that amoxicillin option separately.

How Metronidazole Works

Metronidazole functions as a prodrug. Once it enters an anaerobic bacterium or susceptible protozoan, low-oxygen conditions within the organism reduce its nitro group and generate reactive intermediates. These intermediates damage microbial DNA and disrupt nucleic acid synthesis, ultimately killing the susceptible organism. Because activation depends on an anaerobic or microaerophilic environment, metronidazole has little useful activity against most aerobic bacteria. It may therefore be paired with another antibiotic when an infection involves both aerobic and anaerobic organisms.

Evidence Behind Metronidazole Therapy

Metronidazole is one of the most extensively studied agents for susceptible anaerobic and protozoal infections, with decades of clinical trials and practical experience supporting its use in conditions such as bacterial vaginosis, trichomoniasis, giardiasis, amebiasis, and mixed anaerobic infections. It remains included in major treatment guidelines for several of these conditions. Evidence for a particular extended-release formulation, however, is indication- and product-specific. Results obtained with an immediate-release tablet, vaginal product, or a different extended-release strength should not be used to assume that products are dose-for-dose interchangeable.

Formulation and What Metro Contains

Each Metro tablet contains metronidazole as its active ingredient, formulated as an oral extended-release tablet rather than an immediate-release tablet, capsule, cream, or gel. The extended-release design controls how quickly the active ingredient becomes available after the tablet is swallowed. We offer Metro in 200 mg and 400 mg strengths. The tablet should be swallowed whole with water, following the product-specific instructions provided by the prescriber and dispensing pharmacy.

Established Uses for This Formulation

Metronidazole's established uses span multiple oral and topical dosage forms, but the appropriate use of an extended-release tablet depends on its specific labeling and the prescribed regimen. Immediate-release metronidazole tablets are commonly used for various anaerobic bacterial infections and selected protozoal infections, while extended-release products may use different dose schedules and administration instructions. A prescriber should select the indication, formulation, strength, dosing frequency, and course length based on the diagnosis. Metro should not be substituted dose for dose for another metronidazole formulation without professional direction.

Strengths, Package Options, and General Dosing Principles

We offer Metro 200 mg tablets in packages of 120, 180, 270, or 360 pills. Metro 400 mg tablets are available in packages of 90, 120, 180, 270, or 360 pills. Customers should choose the strength and quantity that match the prescription or other directions provided by their healthcare professional rather than estimating a course from package size alone.

General Dosing Patterns Across Indications

Prescribers base the total daily metronidazole dose, dosing frequency, and number of treatment days on the organism, infection site, dosage form, liver function, and other patient-specific factors. Immediate-release regimens for anaerobic bacterial infections may involve divided doses over seven to fourteen days, while regimens for bacterial vaginosis, trichomoniasis, giardiasis, and amebiasis differ in both dose and duration. These examples describe metronidazole therapy generally and are not instructions for dosing Metro extended-release tablets. Follow the exact strength, schedule, and course length specified for the dispensed product, and do not extend, repeat, or shorten a course on your own.

Food and Administration Instructions

Food instructions can differ between immediate-release and extended-release metronidazole products. Although food may reduce stomach upset with some metronidazole regimens, certain extended-release labeling instructs patients to take the tablet on an empty stomach, such as at least one hour before or two hours after a meal. Follow the instructions supplied with Metro and the directions from your prescriber or pharmacist rather than assuming that it can be taken with food. Swallow the tablet whole; do not crush or chew it.

Elimination and Half-Life

Metronidazole is absorbed after oral dosing and is extensively metabolized in the liver, chiefly through oxidation and glucuronide conjugation. One resulting hydroxy metabolite retains some antimicrobial activity. The plasma half-life of metronidazole in adults with normal liver function is approximately eight hours, although individual values vary. Most of a dose and its metabolites are eliminated in urine, with a smaller amount excreted in stool. An extended-release tablet changes the rate at which the medicine enters the body but does not eliminate the need for a product-specific dosing schedule. People with severe liver impairment may clear metronidazole more slowly and may need a modified regimen and closer monitoring.

Important Safety Information

Metronidazole has several safety considerations beyond routine antibiotic precautions. It can cause central nervous system effects, including dizziness, confusion, hallucinations, impaired coordination, peripheral neuropathy with numbness or tingling in the hands or feet, and, rarely, seizures or encephalopathy. Anyone who develops significant neurological symptoms should stop taking the medicine and contact a healthcare professional promptly. People experiencing dizziness, confusion, vision changes, poor coordination, or similar effects should not drive or operate machinery.

Avoid alcohol and products containing propylene glycol during metronidazole treatment and for at least three days after the final dose, unless the prescribing information provides a longer interval. Combining them may cause abdominal cramps, nausea, vomiting, headache, flushing, or a rapid heartbeat. Pregnant patients should discuss the expected benefits and risks with a prescriber because metronidazole crosses the placenta. Metronidazole also enters human milk at concentrations similar to those in plasma, so breastfeeding parents need individualized advice about whether to interrupt nursing or use a different treatment.

Prescription Status and Ordering Through Us

Oral metronidazole extended-release tablets have prescription-only status in the United States. The active ingredient is authorized for human medicinal use, but that ingredient-level status is separate from the prescription classification of this oral dosage form. Our product-specific requirement for accepting an order is not stated here, so customers should confirm the documentation required by our current ordering process during checkout or with our support team. Our pharmacist-supported team is available 24/7 by email, online chat, or phone to answer questions about ordering, prescription directions, or the supplied medicine. Drugs-24h, operated by Ireland RX, has supported customers since 2008.

Who Should Avoid Metronidazole

Metronidazole is contraindicated in anyone with a known hypersensitivity to metronidazole, another nitroimidazole derivative, or a relevant product ingredient. A general or unspecified allergy history is not by itself a contraindication. Metronidazole should not be used by someone who has taken disulfiram within the previous two weeks because the combination has been associated with psychotic reactions. Alcohol and propylene glycol must also be avoided during treatment and for at least three days afterward.

Severe, sometimes fatal, liver toxicity has been reported in people with Cockayne syndrome. Metronidazole should generally be avoided in these patients unless no suitable alternative is available and the expected benefit outweighs the risk; if it is used, close liver-function monitoring is necessary. Because the safety and effectiveness of oral extended-release metronidazole tablets have not been established in pediatric patients, use in children requires specific professional assessment and selection of an appropriate product.

Drug and Substance Interactions

Metronidazole interacts with a defined set of medicines and substances, summarized below.

This list is not exhaustive. A pharmacist or prescriber should review all prescription medicines, over-the-counter products, and supplements before metronidazole is started. Laboratory tests may also be affected, and blood-count or liver-function monitoring may be appropriate during prolonged therapy or in higher-risk patients.

Side Effects and When to Take Action

Many people tolerate metronidazole with only mild, self-limited effects. Commonly reported problems include nausea, a metallic or bitter taste, mild stomach upset, headache, or dark reddish-brown urine. The urine discoloration is usually caused by a metabolite and is not harmful by itself. Serious reactions are much less common but require prompt medical attention. Warning signs include seizures, marked confusion, hallucinations, impaired coordination, numbness or tingling suggesting peripheral neuropathy, facial swelling or difficulty breathing, and severe skin reactions involving blistering or peeling. The comparison image below separates common effects from serious warning signs and outlines an appropriate response.

If a serious neurological, allergic, or skin reaction develops, stop taking the medicine and obtain urgent medical advice. Call emergency services for difficulty breathing, collapse, a seizure, or another immediately life-threatening symptom rather than waiting to see whether it resolves.

Overdose and Toxicity

Taking substantially more metronidazole than directed can intensify gastrointestinal and neurological effects, causing pronounced nausea, vomiting, dizziness, and an unsteady gait known as ataxia. Large overdoses have also been associated with seizures and peripheral nerve effects. There is no specific antidote, so treatment is supportive and focuses on symptoms and neurological monitoring. In the United States, anyone who has taken more than the prescribed amount or suspects that a child or another person swallowed Metro tablets should promptly contact Poison Control or seek emergency help. Do not wait for symptoms to appear.

Storage Instructions

Store Metro tablets at 68°F to 77°F in a tightly closed, light-resistant container. Protect them from direct light, excess heat, and moisture, and avoid storing them in a humid bathroom cabinet. Keep the tablets out of the reach of children and pets. Proper storage helps preserve the medicine's quality and extended-release characteristics through its labeled shelf life.

Metro vs Immediate-Release Metronidazole, Tinidazole, and Clindamycin

An extended-release tablet may offer a more convenient schedule when its product-specific regimen permits less frequent dosing. Its main trade-off is formulation rigidity: the tablet generally cannot be crushed or chewed, and it should not be substituted dose for dose for an immediate-release product. Immediate-release metronidazole is available in regimens tailored to a wider range of established infections, but some regimens require multiple doses per day.

Tinidazole is a related nitroimidazole with a longer half-life. Depending on the infection, it may be prescribed as a single dose or a shorter course, but it is not appropriate for every condition treated with metronidazole. Clindamycin is another option with activity against certain anaerobic bacteria and is sometimes used for bacterial vaginosis. It does not share metronidazole's alcohol warning, but systemic clindamycin has a particularly important association with Clostridioides difficile-associated diarrhea and colitis. For infections outside metronidazole's spectrum, our Antibiotics section provides navigation to other options that a prescriber may consider.

Generic Metronidazole and Other Alternatives

Metro contains metronidazole, which is also available in immediate-release oral products; you can review that active ingredient on our metronidazole page. Immediate-release and extended-release tablets can differ in strength, release pattern, dosing frequency, food instructions, and established uses, so they should not be exchanged without professional direction.

Vaginal metronidazole gels, including products marketed under names such as Vandazole and Nuvessa, treat bacterial vaginosis locally and generally produce lower systemic exposure than oral treatment. They are not suitable for infections outside the vagina, and clinically relevant precautions can still apply. Tinidazole and secnidazole are related nitroimidazoles used for some overlapping protozoal and vaginal indications, often with shorter regimens. For Clostridioides difficile infection, current practice generally favors oral vancomycin or fidaxomicin over metronidazole when those preferred treatments are suitable and available. Understanding these distinctions helps explain why a prescriber selects a particular nitroimidazole, dosage form, or alternative antibiotic for a specific diagnosis.