Metronidazole (Flagyl): Uses, Dosage, Side Effects, Precautions and Interactions

Uses   |   Mechanism of Action   |   Dosage   |   Side Effects   |   Precautions   |   Interactions   |   Toxicity   |   FAQs | Takeaway

Generic names: Metronidazole

Brand names: Flagyl, Flagystatin, Metrocream, Rosadan, Noritate, Metrogel, Metrolotion, Nidagel, Nuvessa, Vandazole

Drug class: Nitroimidazoles

What is metronidazole?

Metronidazole is a potent antibiotic and antiprotozoal medication used to combat a wide range of bacterial and protozoal infections. It’s available in various forms, including tablets, creams, and intravenous solutions.

What is metronidazole used for?

Metronidazole finds its application in several medical conditions, including:

Bacterial infections: Metronidazole is particularly effective against anaerobic bacteria, which thrive in environments devoid of oxygen. These bacteria are responsible for a range of infections, including but not limited to:

• Bacterial vaginosis: A common vaginal infection characterized by an overgrowth of certain bacteria in the vagina, leading to symptoms such as abnormal vaginal discharge, itching, and odor.
• Intra-abdominal infections: Metronidazole is often used in combination with other antibiotics to treat infections within the abdominal cavity, such as peritonitis and abscesses.

Protozoal infections: Metronidazole is highly effective against various protozoa, which are single-celled microorganisms that can cause serious infections:

• Trichomoniasis: A sexually transmitted infection caused by the parasite Trichomonas vaginalis, leading to symptoms like vaginal discharge and itching in women and urethral discharge in men.
• Giardiasis: An intestinal infection caused by the parasite Giardia lamblia, resulting in diarrhea, abdominal cramps, and other gastrointestinal symptoms.
• Amoebiasis: An infection caused by the amoeba Entamoeba histolytica, which can affect the intestines and liver, leading to symptoms such as dysentery and liver abscesses.

Dental and oral infections: Metronidazole is sometimes prescribed in combination with other antibiotics to treat dental and oral infections, particularly when anaerobic bacteria are involved. This may include conditions like dental abscesses and periodontal disease.

Helicobacter pylori infection: Metronidazole is part of the treatment regimen for Helicobacter pylori infection, a bacterial infection associated with stomach ulcers and gastritis. When used in combination with other antibiotics, it helps eradicate the bacteria, facilitating the healing of gastric ulcers.

Inflammatory bowel disease (IBD): In some cases, metronidazole may be prescribed to manage symptoms of IBD, such as Crohn’s disease and ulcerative colitis. It is believed to help reduce inflammation in the intestines and control certain symptoms during flare-ups.

Other uses: Metronidazole may be employed in the treatment of other conditions, such as rosacea, a chronic skin condition, where it can help reduce the inflammation and redness associated with the disorder.

What is the mechanism of action of metronidazole?

Metronidazole’s mechanism of action is unique and primarily revolves around its ability to disrupt and interfere with the DNA and metabolic processes of certain microorganisms.

• Activation within microorganisms: Metronidazole is administered in an inactive form and does not exhibit its antimicrobial properties until it is taken up by susceptible microorganisms, such as bacteria and protozoa. Once inside the microorganism, metronidazole undergoes a chemical transformation through the action of cellular enzymes.
• Formation of reactive species: The transformed metronidazole generates reactive species, including nitro radicals, within the microbial cells. These reactive species are highly toxic and unstable molecules.
• DNA damage: One of the primary targets of metronidazole’s action is the DNA within the microbial cells. The reactive species produced by metronidazole inflict severe damage on the DNA structure. They cause breaks in the DNA strands and interfere with the replication and repair processes.
• Inhibition of DNA synthesis: Metronidazole disrupts the synthesis of new DNA molecules within the microbial cells. This prevents the microorganisms from replicating their genetic material, which is crucial for their survival and multiplication.
• Disruption of metabolism: Metronidazole also interferes with the metabolic processes of microorganisms. It impairs their ability to generate energy through the tricarboxylic acid (TCA) cycle, a key metabolic pathway. This disruption of energy production further weakens the microorganisms.
• Toxic effects: The accumulation of DNA damage and metabolic disruptions leads to toxic effects within the microbial cells. These effects include the inhibition of cell division, disruption of cell membranes, and overall cellular dysfunction.
• Microbial death: The cumulative impact of metronidazole’s actions on DNA and metabolism ultimately results in the death of the microorganisms. This antimicrobial effect is particularly effective against anaerobic microorganisms, which are susceptible to metronidazole due to their unique metabolic pathways.

What is the dosage for metronidazole?

The dosage can vary depending on the specific medical condition being treated, the patient’s age, weight, and overall health, as well as the form of the medication (oral, topical, intravenous, etc.). It is crucial to follow the prescribed dosage and instructions provided by a healthcare professional to ensure the safe and effective use of metronidazole.

Bacterial vaginosis:

• Oral tablets: The usual adult dose is 500 mg twice daily for 7 days. Alternatively, a single 2-gram dose can be administered as a one-time treatment.
• Vaginal gel: A healthcare provider may prescribe a 0.75% metronidazole vaginal gel, which is inserted into the vagina once daily for 5 days.

Trichomoniasis:

• The typical adult dose is 2 grams (g) as a single oral dose or 250 mg three times daily for 7 days.

Anaerobic infections (Intra-abdominal, Gynecological, Skin and Soft Tissue, etc.):

• The adult dosage is typically 500 mg to 750 mg orally every 6 to 8 hours. In severe infections, the dosage may be increased to 1 gram every 6 hours.

Giardiasis:

• For adults and children over 3 years of age, the usual dose is 250 mg orally three times daily for 5 to 7 days.

Amoebiasis:

• The recommended adult dosage is usually 750 mg to 1 gram orally three times daily for 5 to 10 days, followed by a course of luminal (intestinal) amoebiasis treatment if needed.

Helicobacter pylori infection:

• As part of combination therapy for H. pylori eradication, metronidazole is often prescribed at a dose of 500 mg to 750 mg twice daily for 7 days along with other antibiotics and acid-suppressing drugs.

Rosacea:

• For the topical treatment of rosacea, metronidazole is available as a cream, gel, or lotion. Typically, a thin layer is applied to the affected skin area once or twice daily, as directed by a healthcare provider.

What are the side effects of metronidazole?

While metronidazole is highly effective like all medications, it can potentially cause side effects in some individuals. It’s essential to be aware of these side effects and discuss them with your healthcare provider before and during the course of treatment.

Common side effects:

• Nausea and vomiting: Gastrointestinal upset is one of the most common side effects of metronidazole. This may include nausea, vomiting, and a metallic taste in the mouth.
• Diarrhea: Some individuals may experience diarrhea as a side effect of metronidazole.
• Headache: Headaches are another relatively common side effect.
• Loss of appetite: metronidazole can lead to a temporary loss of appetite or a feeling of fullness.
• Metallic taste in the mouth.
• Dry mouth.
• Changes in the sense of taste.

Less common side effects:

• Dizziness: Some people may experience dizziness or a lightheaded feeling.
• Nervous system effects: In rare cases, metronidazole can affect the central nervous system, leading to symptoms such as confusion, irritability, or hallucinations.
• Dark urine: metronidazole can cause the urine to become dark in color.
• Peripheral neuropathy: Prolonged use of metronidazole, especially at high doses, may rarely lead to peripheral neuropathy, which involves tingling or numbness in the extremities.
• Allergic reactions: While allergic reactions to metronidazole are relatively rare, they can be serious. Symptoms may include hives, rash, itching, swelling of the face, lips, or tongue, and difficulty breathing. Seek immediate medical attention if you experience any of these symptoms.

It’s important to note that the majority of people who take metronidazole do not experience severe side effects.

What are the precautions to consider when taking metronidazole?

When using metronidazole, it’s important to take certain precautions to ensure its safe and effective use. The following precautions can help minimize risks and optimize your treatment.

• Prescription only: metronidazole is a prescription medication. Always use it under the guidance and supervision of a qualified healthcare professional. Do not self-medicate or share the medication with others.
• Medical history: Inform your healthcare provider of your complete medical history, including any allergies, liver disease, kidney disease, blood disorders, and a history of nervous system disorders. This information can help determine the appropriate dosage and monitor potential risks.
• Pregnancy and breastfeeding: If you are pregnant or planning to become pregnant, or if you are breastfeeding, discuss the risks and benefits of metronidazole with your healthcare provider. In some cases, alternative medications may be recommended.
• Alcohol avoidance: Metronidazole can cause a disulfiram-like reaction when combined with alcohol, leading to severe nausea, vomiting, and headache. Avoid alcohol consumption during treatment with metronidazole and for at least 48 hours after the last dose.
• Allergies: If you have a known allergy to metronidazole or similar medications (such as tinidazole), let your healthcare provider know immediately. Allergic reactions can be serious and may require alternative treatments.
• Driving and operating machinery: Metronidazole may cause dizziness or drowsiness in some individuals. If you experience these side effects, avoid driving or operating heavy machinery until you are sure you can do so safely.
• Complete the full course: Finish the entire prescribed course of metronidazole, even if your symptoms improve before you have taken all the medication. Stopping the treatment early can allow the infection to persist or develop resistance to the medication.

What drugs interact with metronidazole?

Metronidazole has the potential to interact with other drugs, which could either impact their efficacy or lead to undesirable side effects. Inform your healthcare provider about all the drugs and supplements you are taking to avoid potential interactions.

• Alcohol: Combining metronidazole with alcohol can lead to a disulfiram-like reaction. This reaction includes symptoms such as severe nausea, vomiting, headache, and an overall feeling of discomfort. Even small amounts of alcohol can trigger this reaction.
• Warfarin (Coumadin): Metronidazole can potentiate the effects of the blood-thinning medication warfarin, increasing the risk of bleeding.
• Lithium: Metronidazole may increase the levels of lithium in the blood, potentially leading to lithium toxicity.
• Phenytoin (Dilantin) and other antiseizure medications: Metronidazole can alter the metabolism of antiseizure medications like phenytoin, leading to changes in their blood levels.
• Cimetidine (Tagamet): Cimetidine, an acid-reducing medication, can increase the blood levels of metronidazole.
• Anticoagulants and antiplatelet drugs: Metronidazole can increase the risk of bleeding when taken with anticoagulants (e.g., heparin) and antiplatelet drugs (e.g., aspirin).
• Disulfiram (Antabuse): Disulfiram is a medication used to treat alcohol addiction. When combined with metronidazole, it can increase the risk of a disulfiram-like reaction (similar to the reaction seen with alcohol).

Toxicity

In cases of overdose or prolonged use of high doses, metronidazole can lead to toxicity, causing neurological symptoms like seizures, peripheral neuropathy and liver toxicity. It’s essential to adhere to the prescribed dosage and seek medical help if you suspect an overdose.

Frequently Asked Questions (FAQ)

Takeaway

Metronidazole is an effective antibiotic commonly used to treat a variety of bacterial and protozoal infections. Its versatility and wide-ranging applications make it a valuable tool in modern medicine, but its usage should be guided by a healthcare professional to ensure proper treatment and minimize potential side effects.