Flagyl ER (metronidazole extended-release) is a prescription antibiotic and antiprotozoal medication designed for the systemic treatment of serious anaerobic bacterial infections and certain parasitic conditions. Its advanced extended-release formulation ensures sustained therapeutic plasma levels, enhancing efficacy while potentially improving dosing convenience. This medication is indicated for use in adults and should be administered under strict medical supervision due to its specific activity against susceptible organisms and notable safety considerations.

Features

• Contains metronidazole as the active ingredient in an extended-release formulation
• Available in 750 mg tablets
• Designed for once-daily oral administration
• Exhibits bactericidal activity against a wide range of anaerobic bacteria
• Demonstrates antiprotozoal activity against organisms including Giardia lamblia, Trichomonas vaginalis, and Entamoeba species
• Features pH-dependent delayed release to target optimal absorption in the small intestine

Benefits

• Provides sustained therapeutic drug levels throughout the dosing interval
• Reduces dosing frequency compared to immediate-release formulations
• Effectively treats serious anaerobic infections including intra-abdominal infections, skin and skin structure infections, and bacterial vaginosis
• Demonstrates excellent tissue penetration, reaching therapeutic concentrations at infection sites
• Offers reliable treatment for protozoal infections including amebiasis and trichomoniasis
• May improve adherence through simplified once-daily dosing regimen

Common use

Flagyl ER is primarily prescribed for the treatment of serious infections caused by susceptible anaerobic bacteria. Common indications include complicated intra-abdominal infections (such as those involving Bacteroides species, Clostridium species, and Peptostreptococcus species), skin and skin structure infections, gynecological infections including bacterial vaginosis, and as part of combination therapy for Helicobacter pylori eradication. Additionally, it is used for the treatment of amebiasis (both intestinal and extraintestinal), trichomoniasis, and giardiasis. The extended-release formulation is specifically designed for conditions requiring prolonged metronidazole therapy where once-daily dosing is appropriate.

Dosage and direction

The recommended dosage for Flagyl ER is 750 mg taken orally once daily, typically for 7 to 10 days depending on the infection being treated. For bacterial vaginosis, the treatment course is typically 5 days. Tablets should be swallowed whole with a full glass of water and should not be crushed, chewed, or split. Administration with food may help minimize gastrointestinal upset. The timing of doses should be consistent each day, and treatment should continue for the full prescribed duration even if symptoms improve earlier. Dosage adjustments are necessary in patients with severe hepatic impairment, with recommendations typically involving either extended dosing intervals or reduced doses based on therapeutic drug monitoring.

Precautions

Patients should be advised that Flagyl ER may cause dizziness, drowsiness, or visual disturbances and should exercise caution when operating machinery or driving. Alcohol consumption must be avoided during therapy and for at least 72 hours after completion due to the risk of a disulfiram-like reaction characterized by nausea, vomiting, flushing, and tachycardia. Regular monitoring of blood counts is recommended during prolonged therapy due to potential hematological effects. Patients with history of blood dyscrasias, central or peripheral nervous system disorders, or hepatic impairment require close supervision. The medication may cause urine to darken, which is harmless but should be explained to patients to prevent concern.

Contraindications

Flagyl ER is contraindicated in patients with known hypersensitivity to metronidazole, other nitroimidazole derivatives, or any component of the formulation. It is contraindicated during the first trimester of pregnancy due to potential fetal risk. Use is prohibited in patients with active central nervous system disorders, including epilepsy and other seizure disorders. Concurrent administration with disulfiram is contraindicated due to increased risk of psychotic reactions. The medication should not be administered to patients who have taken alcohol within recent hours or who cannot abstain from alcohol during treatment.

Possible side effect

Common adverse reactions include nausea (approximately 10-12%), headache (8-10%), metallic taste (8-9%), and anorexia (5-7%). Gastrointestinal effects such as vomiting, diarrhea, abdominal discomfort, and constipation may occur. Neurological effects including dizziness, vertigo, incoordination, and peripheral neuropathy (especially with prolonged use) have been reported. Less frequently, patients may experience reversible neutropenia, thrombophlebitis, darkened urine, vaginal dryness or burning, and allergic reactions ranging from mild rash to Stevens-Johnson syndrome. Seizures and encephalopathy have been reported rarely, particularly at high doses or in patients with predisposing factors.

Drug interaction

Metronidazole exhibits significant interactions with warfarin and other coumarin anticoagulants, potentiating their effects and requiring close monitoring of prothrombin time. Concurrent use with alcohol produces disulfiram-like reactions. Medications that induce hepatic enzymes (phenobarbital, phenytoin) may decrease metronidazole concentrations, while those that inhibit these enzymes may increase levels. Cimetidine may prolong metronidazole’s half-life and increase plasma concentrations. Lithium levels may increase during concurrent therapy, necessitating monitoring. Metronidazole may increase serum levels of fluorouracil, phenytoin, and cyclosporine. Concomitant administration with disulfiram should be avoided due to increased risk of psychotic reactions.

Missed dose

If a dose of Flagyl ER is missed, it should be taken as soon as remembered on the same day. However, if it is near the time for the next scheduled dose, the missed dose should be skipped and the regular dosing schedule resumed. Patients should not take a double dose to make up for a missed dose. Maintaining consistent dosing intervals is important for maintaining therapeutic drug levels. If multiple doses are missed or there is uncertainty about how to proceed, patients should consult their healthcare provider for guidance rather than adjusting the regimen independently.

Overdose

Overdose with Flagyl ER may manifest as nausea, vomiting, ataxia, seizures, and peripheral neuropathy. In severe cases, neurotoxicity including encephalopathy and cerebellar symptoms may occur. There is no specific antidote for metronidazole overdose. Management involves supportive care including gastric lavage if presentation is early, activated charcoal to prevent further absorption, and symptomatic treatment. Seizures may require benzodiazepines or other anticonvulsants. Hemodialysis may be considered in severe cases as it can accelerate elimination, though its effectiveness is limited by metronidazole’s large volume of distribution. Patients should receive neurological monitoring and supportive care until symptoms resolve.

Storage

Flagyl ER tablets should be stored at controlled room temperature between 20°C to 25°C (68°F to 77°F), with excursions permitted between 15°C to 30°C (59°F to 86°F). The medication should be kept in its original container with the lid tightly closed to protect from moisture and light. Tablets should not be stored in bathroom cabinets or other areas with high humidity. Keep out of reach of children and pets. Do not use tablets that show signs of damage, discoloration, or that have expired. Proper disposal of unused medication should follow local regulations or medication take-back programs.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Flagyl ER is a prescription medication that should be used only under the supervision of a qualified healthcare professional. The prescribing physician should be consulted for diagnosis, treatment decisions, and complete prescribing information including boxed warnings. Individual patient response and appropriate therapeutic regimens may vary based on specific clinical circumstances. Patients should not initiate, adjust, or discontinue medication without professional medical guidance.

Reviews

Clinical studies demonstrate that Flagyl ER provides equivalent efficacy to immediate-release metronidazole with the advantage of once-daily dosing. In trials involving intra-abdominal infections, clinical cure rates ranged from 85-92% with the extended-release formulation. For bacterial vaginosis, studies show clinical cure rates of 75-85% with the 5-day regimen. Patients generally report satisfaction with the reduced dosing frequency, though gastrointestinal side effects remain comparable to the immediate-release formulation. Healthcare providers note the convenience of once-daily dosing for improving adherence in outpatient settings, particularly for longer treatment courses. The extended-release profile is particularly valued in cases where maintaining consistent drug levels is critical for therapeutic success.