Metronidazole

What is Metronidazole?

Metronidazole is an antibiotic and antiprotozoal medication that belongs to the nitroimidazole class of drugs. It is primarily used to treat infections caused by anaerobic bacteria and certain parasites, including conditions affecting the gastrointestinal tract, reproductive system, and skin. This medication is available in oral, topical, and intravenous formulations.

Uses

Metronidazole is prescribed for several types of infections:

• Bacterial vaginosis: Treats overgrowth of harmful bacteria in the vagina that causes discharge and odor
• Trichomoniasis: Eliminates the parasitic infection that affects the urogenital tract in both men and women
• Clostridioides difficile colitis: Treats severe intestinal infections caused by C. diff bacteria, often occurring after antibiotic use
• Anaerobic bacterial infections: Combats serious infections in the abdomen, pelvis, and other body areas where oxygen levels are low
• Helicobacter pylori eradication: Used in combination therapy to treat stomach ulcers caused by H. pylori bacteria
• Rosacea: Topical formulations help reduce inflammation and pustules associated with this skin condition

How it works

Metronidazole works by entering bacterial and parasitic cells and interfering with their DNA synthesis. Once inside susceptible organisms, the drug is converted into toxic compounds that damage the microorganism’s genetic material, ultimately leading to cell death. This mechanism is particularly effective against anaerobic bacteria and certain parasites that lack the protective enzymes found in human cells.

Side effects

Common side effects include:

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• Nausea and vomiting
• Metallic taste in mouth
• Loss of appetite
• Abdominal cramping
• Diarrhea
• Headache
• Dizziness
• Dark-colored urine

Serious side effects requiring immediate medical attention:

• Severe allergic reactions with rash, swelling, or difficulty breathing
• Numbness or tingling in hands and feet (peripheral neuropathy)
• Seizures or confusion
• Severe diarrhea that may indicate C. diff infection
• Signs of liver problems including yellowing of skin or eyes

Warnings and precautions

• Pregnancy considerations: Generally avoided during the first trimester of pregnancy; use during later pregnancy only when benefits outweigh risks
• Neurological effects: Patients with a history of seizures or neurological disorders should use with caution due to potential nervous system side effects
• Liver disease: Dosage adjustment may be necessary in patients with severe liver impairment as the drug is metabolized by the liver
• Blood disorders: Regular monitoring may be needed during prolonged treatment as the medication can affect blood cell counts
• Alcohol avoidance: Complete abstinence from alcohol is required during treatment and for at least 48 hours after the last dose to prevent severe nausea and vomiting

Interactions

• Warfarin: Metronidazole significantly increases bleeding risk by enhancing warfarin’s anticoagulant effects
• Lithium: Can increase lithium levels in blood, potentially causing lithium toxicity
• Phenytoin: May increase phenytoin levels, requiring dose adjustments to prevent seizure medication toxicity
• Alcohol: Causes severe disulfiram-like reaction with nausea, vomiting, and flushing
• Disulfiram: Combination may cause confusion and psychotic reactions
• Cyclosporine: Can increase cyclosporine levels, potentially causing kidney toxicity
• Fluorouracil: May increase cancer drug toxicity by reducing its breakdown
• Cimetidine: Can increase metronidazole levels by inhibiting its metabolism

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Dosage

Typical adult dosages vary by condition and formulation. For bacterial vaginosis, the usual dose is 500 mg twice daily for 7 days orally, or 750 mg extended-release tablets once daily for 7 days. For trichomoniasis, a single 2-gram dose or 500 mg twice daily for 7 days is commonly prescribed. C. difficile infections typically require 500 mg three times daily for 10-14 days. Topical preparations for rosacea are usually applied twice daily to affected areas. Dosage adjustments may be necessary based on kidney or liver function, age, and severity of infection. Always follow your healthcare provider’s specific dosing instructions, as they will determine the most appropriate regimen based on your individual condition and medical history.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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