What Is Metronidazole Used for? A Complete Guide

Written By: Dr. Diana Rangraves, PharmD

Are you someone who’s just been prescribed metronidazole and wants to understand more about it? Or maybe you’re a healthcare professional looking to deepen your knowledge of how and when to prescribe this medication.

Whether you’re managing a new prescription or seeking expert insights, you’re in the right place. We’ll explore everything you need to know about metronidazole — what it is, the conditions it treats, how it works, and when healthcare providers typically recommend it.

Conditions Metronidazole Treats

Metronidazole is a versatile antibiotic and antiprotozoal agent commonly used to treat a range of infections caused by anaerobic bacteria and certain parasites. Below are some of the infections treated by metronidazole.

Bacterial Vaginosis (BV)

Bacterial vaginosis is a common infection in women caused by an imbalance of bacteria in the vagina. Symptoms may include unusual discharge, odor, and discomfort. Metronidazole, typically administered as an oral tablet or a topical gel, is highly effective in treating BV by restoring the balance of bacteria in the vaginal area. It’s often the first-choice treatment due to its targeted action against anaerobic bacteria [1].

Trichomoniasis

Trichomoniasis is a sexually transmitted infection (STI) caused by the parasite Trichomonas vaginalis. Though many people are asymptomatic, this infection can cause symptoms like itching, discomfort, and discharge [2]. Metronidazole is the most commonly prescribed treatment for Trichomoniasis, as it effectively eradicates the parasite. Generally, a single dose or a short course is sufficient for treating this STI [3].

Dental Infections

Metronidazole is widely used to treat infections within the mouth, such as abscesses or periodontal (gum) disease [4]. Dental infections are often caused by anaerobic bacteria, which thrive in low-oxygen environments like deep gum pockets. Metronidazole’s effectiveness against anaerobes makes it particularly useful in dental practice, often prescribed in combination with other antibiotics like amoxicillin.

Skin Infections

Metronidazole also plays a role in treating skin infections, especially those associated with conditions like rosacea, where redness and inflammation can occur. When used as a topical cream or gel, it can reduce inflammation and target bacterial infection on the skin. It’s an option for patients who need local treatment with minimal systemic side effects [5].

Urinary Tract Infections (UTIs)

While not always the first choice for UTIs, metronidazole can be used for specific types of UTIs caused by anaerobic bacteria. In cases where typical UTI antibiotics aren’t effective or where anaerobic infection is suspected, metronidazole might be prescribed. This is more common in recurrent or complicated UTI cases.

Other Conditions

In addition to the primary infections mentioned, here are other metronidazole uses:

• Gastrointestinal infections, such as diverticulitis or certain forms of colitis, often alongside other antibiotics [6]
• Helicobacter pylori infections, where it’s used as part of a combination therapy to target the bacteria responsible for stomach ulcers [7]

How Metronidazole Works

To understand why metronidazole is so effective, it helps to look at its dual role as both an antibacterial and antiprotozoal agent.

Antibacterial Properties

Metronidazole is especially effective against anaerobic bacteria—types of bacteria that thrive in environments with little to no oxygen [8]. This includes many of the harmful bacteria found in the gut, reproductive system, and deep tissues. When metronidazole is administered, it enters bacterial cells and disrupts DNA synthesis, ultimately leading to bacterial cell death. This targeted action makes it highly effective for infections that other antibiotics may not reach or fully eradicate.

Antiprotozoal Properties

Metronidazole is also effective against certain protozoa, specifically Trichomonas vaginalis, Entamoeba histolytica, and Giardia lamblia [9]. Its antiprotozoal action also involves DNA disruption, preventing protozoal parasites from replicating and ultimately killing the pathogen.

Mechanism of Action

Once metronidazole enters the body, it is reduced by the anaerobic cells of bacteria and protozoa. This reduction activates the drug, allowing it to interact with the DNA of the microorganisms, thereby inhibiting nucleic acid synthesis. This process disrupts the genetic material and cellular function of harmful bacteria and protozoa, leading to their eventual death [10].

Why Doctors Might Prescribe Metronidazole Over Other Antibiotics

There are specific cases where healthcare providers will choose metronidazole over other antibiotics, thanks to its unique strengths.

Unique Strengths of Metronidazole

One of the key advantages of metronidazole is its efficacy against anaerobic bacteria and protozoa. Many antibiotics are either not effective or less effective against these pathogens. For infections where anaerobic bacteria are the primary cause — such as dental abscesses or certain intra-abdominal infections — metronidazole is often the preferred choice. Similarly, its dual action against protozoa makes it invaluable in treating trichomoniasis and other protozoal infections.

Factors Influencing Prescription

Several factors influence a doctor’s decision to prescribe metronidazole, including:

• Infection Type: For anaerobic or mixed infections, metronidazole may be prescribed as a stand-alone or adjunct therapy.
• Patient History: Patients with allergies to certain antibiotics, like penicillin, may be prescribed metronidazole as an alternative.
• Drug Resistance: Metronidazole may be prescribed when resistance to other antibiotics is detected, especially in cases of recurrent infections.

Considerations and Limitations

While metronidazole is versatile, it’s not suitable for every infection. For example, it’s not effective against aerobic bacteria (those that require oxygen), so it won’t work for infections caused by these organisms. In such cases, doctors may opt for other antibiotics like amoxicillin or ciprofloxacin.

Dosage and Forms of Metronidazole

Understanding the appropriate dosage and form of metronidazole is essential for effective treatment.

Common Dosages and Treatment Durations

Dosages vary based on the condition being treated:

• Bacterial Vaginosis: A common regimen is 500 mg twice daily for 7 days [11].
• Trichomoniasis: Usually a single 2 g dose or 500 mg twice daily for 7 days [11].

Treatment duration may be adjusted based on the infection’s severity and patient response.

Different Forms of Metronidazole

Metronidazole is available in several forms, including:

• Oral Tablets: The most common form used for internal infections.
• Topical Creams and Gels: Often prescribed for skin conditions like rosacea.
• IV Form: Used in hospitals for severe or systemic infections where oral administration isn’t possible.

Healthcare providers select the form based on the location and type of infection to maximize the drug’s effectiveness.

Potential Side Effects and Precautions

Like all medications, metronidazole has potential side effects. While many are mild, some can be serious and require attention.

Common Side Effects

Common, mild side effects include [12]:

• Nausea and Vomiting: Often minimized by taking metronidazole with food
• Headache: Usually mild and resolves on its own
• Metallic Taste: A temporary side effect that many patients experience

Serious Side Effects

Though rare, serious side effects include [12]:

• Bad stomach pains, which may reach through to your back
• Unexpected infections, mouth ulcers, bruising, bleeding gums, or extreme tiredness
• Blurred vision
• The white of the eyes turns yellow
• The skin turns yellow

Precautions and Drug Interactions

Certain precautions should be taken when using metronidazole:

• Avoid Alcohol: Metronidazole interacts with alcohol, causing nausea, vomiting, and cramps. It’s important to avoid alcohol during and for at least 48 hours after treatment.
• Interactions With Other Medications: Metronidazole may interact with blood thinners, seizure medications, and certain other drugs. Always discuss all medications with your doctor before starting treatment.

How To Take Metronidazole for Best Results

Stick to Your Prescribed Dosage

Metronidazole should always be taken at the exact dosage your healthcare provider prescribes. Depending on the type and severity of the infection, you might take it once, twice, or even three times daily. Sticking to this schedule helps maintain the right medication levels in your body.

Complete the Full Course

Even if your symptoms start improving before the medication is finished, it’s essential to take metronidazole for the full prescribed period. Stopping too soon can allow the infection to return or lead to antibiotic resistance.

Avoid Alcohol During Treatment

Metronidazole has a strong interaction with alcohol, which can cause severe nausea, vomiting, cramps, headaches, and flushing. To avoid these reactions, it’s important to avoid alcohol entirely while taking the medication and for at least 48 hours after finishing it.

Be Consistent With Timing

If you’re taking metronidazole more than once daily, try to space doses evenly. This consistency keeps a steady amount of medication in your system, which is essential for fighting infections effectively.

Everlywell: Take Control of Your Health

Metronidazole is an effective, versatile antibiotic commonly prescribed for various bacterial and protozoal infections. Its ability to target harmful bacteria and parasites plays a key role in treating conditions that other antibiotics may not address. However, as with any medication, it’s essential to understand flagyl uses, potential side effects, and precautions.

If you’re experiencing symptoms like unusual discharge, abdominal pain, or unexplained fatigue, identifying the cause is the first step. Companies like Everlywell offer convenient, at-home testing kits that can help you gain insights into your health and determine whether you might benefit from a consultation with your doctor about infections treatable by antibiotics like metronidazole.

With Everlywell’s easy-to-use test kits, you can check for common infections or imbalances from the comfort of your home, making it simpler to take control of your health.

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References

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2. NHS UK. Trichomoniasis. nhs.uk. Last reviewed November 3, 2021. Accessed November 3, 2024. Medical Citation URL.
3. NHS UK. Trichomoniasis Treatment. nhs.uk. Last reviewed November 3, 2021. Accessed November 3, 2024. Medical Citation URL.
4. Metronidazole (topical route). Mayo Clinic. Last updated January 31, 2024. Accessed November 3, 2024. Medical Citation URL.
5. Metronidazole: MedlinePlus drug information. Last updated December 15, 2023. Accessed November 3, 2024. Medical Citation URL.
6. Ribaldone DG, Astegiano M, Saracco G, Pellicano R. Amoxycillin and metronidazole therapy for helicobacter pylori eradication: a 10-year trend in Turin, Italy. Balkan Med J. 2017;34(3):290-291. doi:10.4274/balkanmedj.2015.1714
7. Löfmark S, Edlund C, Nord CE. Metronidazole is still the drug of choice for treatment of anaerobic infections. Clin Infect Dis. 2010;50 Suppl 1:S16-S23. doi:10.1086/647939.
8. Wiid L, Naidoo V. Veterinary pharmaceuticals and declining Cape Griffon Vulture (Gyps coprotheres) numbers: A potential threat to developing embryos. Environ Toxicol Pharmacol. 2023;102:104244. doi:10.1016/j.etap.2023.104244.
9. Weir CB, Le JK. Metronidazole. In: StatPearls. StatPearls Publishing; June 26, 2023. Medical Citation URL.
10. Centers for Disease Control and Prevention. Bacterial Vaginosis. Last reviewed July 22, 2021. Accessed November 3, 2024. Medical Citation URL.
11. Centers for Disease Control and Prevention. Trichomoniasis. Last reviewed September 21, 2022. Accessed November 3, 2024. Medical Citation URL.
12. NHS UK. Side effects of metronidazole. nhs.uk. Last reviewed November 17, 2021. Accessed November 3, 2024. Medical Citation URL.