Is it OK to take expired metronidazole?

Quick Answer

It is generally not recommended to take expired metronidazole. Metronidazole is an antibiotic that can be used to treat certain bacterial and parasitic infections. When metronidazole expires, it may become less effective at treating infections. Taking expired metronidazole can also potentially cause side effects or toxicity. If you have expired metronidazole, it is best to properly dispose of it and get a new, non-expired prescription from your doctor. Do not take expired antibiotics unless specifically instructed to do so by a medical professional.

What is metronidazole?

Metronidazole is an antibiotic medication that is used to treat certain bacterial and parasitic infections in humans and animals. Some of the infections that metronidazole may be used to treat include:

  • Bacterial vaginosis
  • Pelvic inflammatory disease
  • Endocarditis
  • Intra-abdominal infections
  • Skin and skin structure infections
  • Bone and joint infections
  • Central nervous system infections
  • Respiratory tract infections
  • Gastrointestinal infections
  • Amebiasis
  • Giardiasis
  • Trichomoniasis
  • Dental infections

Metronidazole belongs to a class of antibiotics called nitroimidazoles. It works by disrupting the DNA of bacterial and parasitic cells, preventing them from multiplying and surviving.

Some common brand names for metronidazole include Flagyl, Metryl, Metrogel, Metrogyl, and Protostat. It comes in oral tablet, intravenous, vaginal gel, and topical formulations.

Does metronidazole expire?

Yes, metronidazole does have an expiration date. The expiration date is printed on the medication packaging or bottle.

Like most medications, metronidazole begins to degrade after its expiration date has passed. The medication may experience some changes, including:

  • Decreased potency – Expired metronidazole may not be as effective at killing bacteria or parasites as when it was not expired.
  • Change in chemical composition – The chemical makeup of the drug may start to change over time after expiration.
  • Discoloration or change in smell/taste – Expired metronidazole pills or liquids may start to look discolored or smell differently.

The expiration date takes into account testing that manufacturers do to determine how long the medication remains stable and effective under proper storage conditions. However, degradation can happen more quickly if metronidazole is not stored properly, such as at excessively high or low temperatures or humidity.

Is it dangerous to take expired metronidazole?

It is generally not recommended to take expired metronidazole. Since expired metronidazole may have reduced potency, it may not treat infections effectively.

Taking expired metronidazole can also potentially lead to negative side effects or toxicity:

  • Ineffective treatment – Expired metronidazole may not fully get rid of the infection it was meant to treat.
  • Antibiotic resistance – Bacteria and parasites could become resistant to metronidazole if exposed to low doses from expired medication.
  • Side effects – Degraded chemical compounds in expired metronidazole could potentially cause side effects like nausea, vomiting, diarrhea, metallic taste, or yeast infections.
  • Toxicity – Although rare, taking degraded expired metronidazole could potentially cause neurotoxic effects like numbness, tingling, seizures, or encephalopathy.

If you have an active bacterial or parasitic infection that requires antibiotic treatment, it is important to take a full course of non-expired metronidazole exactly as prescribed by your physician. Taking expired metronidazole could fail to properly treat the infection and lead to worsening or recurring illness.

Does expired metronidazole become toxic?

Expired metronidazole is not necessarily toxic. When stored properly, metronidazole is generally stable past its expiration date.

However, there have been isolated reports of mutated or degraded chemical compounds in expired metronidazole causing neurotoxic effects in some situations.

Potential neurotoxicity symptoms include:

  • Tingling or numbness in the hands, feet, arms, or legs
  • Difficulty coordinating muscle movements
  • Slurred speech
  • Vision problems
  • Vertigo
  • Vomiting
  • Seizures
  • Encephalopathy (brain disease, swelling, or damage)

These neurotoxicity reactions are very rare in most people taking regular doses of non-expired metronidazole. But there is a small risk that taking degraded, expired metronidazole could potentially increase neurotoxicity in susceptible individuals.

If concerning neurological symptoms appear after taking expired metronidazole, seek prompt medical attention.

How long does metronidazole last past its expiration date?

It is difficult to predict exactly how long metronidazole will remain stable past its printed expiration date. The medication packaging lists an expiration date that the manufacturer can guarantee potency and safety up until.

However, metronidazole is generally thought to retain much of its effectiveness for some time past expiration, especially if stored properly:

  • Oral metronidazole tablets may last around 1-2 years past their printed expiration date if stored in a cool, dry environment.
  • Metronidazole topical creams or gels also typically remain stable for 1-2 years past expiration if unopened and stored properly.
  • Opened oral or topical metronidazole products may lose potency more quickly and should not be used far past expiration.
  • Metronidazole vaginal gel also remains relatively stable for around 1 year past expiration if tubes are unopened and properly stored.

However, it is impossible to guarantee an exact shelf life past the printed expiration date. Over time, metronidazole potency will decline and potential risks increase. It is best practice to discard expired metronidazole and get a fresh prescription rather than take an expired product.

What are the signs that metronidazole has spoiled?

There are a few signs that may indicate your metronidazole medication has spoiled and should no longer be taken:

  • Expired date on packaging has passed
  • Tablets appear cracked, discolored, or crumbling
  • Unpleasant odor from pills, creams, or gels
  • Liquid solutions are cloudy or contain sediment
  • Creams or gels change texture, consistency, or color
  • Medication was not stored properly, such as at high temperature/humidity
  • Packaging has been damaged

If your metronidazole shows any signs of damage, expiration, or improper storage, it is safest to stop using it and get a new prescription from your healthcare provider. Do not take metronidazole that may have spoiled, even if your symptoms persist.

Can expired metronidazole still work?

Expired metronidazole may still have some antimicrobial properties past its expiration date if properly stored. However, it will become less and less effective over time as the active medication decomposes.

Taking expired metronidazole is risky because even if the medication still provides some benefit, it may not fully treat the bacterial or parasitic infection. This could lead to:

  • Bacteria or parasites persisting in your body
  • Recurring symptoms of infection
  • Antibiotic resistance developing
  • Need for a longer, more intensive course of non-expired antibiotics to properly treat the infection

So while expired metronidazole stored under ideal conditions might still inhibit some microbial growth compared to no treatment, it is generally not worth the risks. Get a full prescription of non-expired metronidazole from your doctor to effectively treat active infections.

Is it safe to take metronidazole after its expiration date?

It is generally unsafe to take metronidazole after its printed expiration date. While expired metronidazole is not guaranteed to be toxic, its effectiveness and chemical composition can begin degrading.

Potential risks of taking expired metronidazole include:

  • Not fully treating bacterial or parasitic infections
  • Increased chance of side effects
  • Development of antibiotic resistance
  • Very small chance of neurotoxicity from chemical degradation

For safety, you should not take expired antibiotics like metronidazole unless explicitly told to do so by a doctor. Getting a fresh fill of non-expired metronidazole is recommended if you have an active infection requiring antibiotic treatment. Discard expired metronidazole products by mixing them with an unpalatable substance like dirt, cat litter, or coffee grounds before throwing them in the trash to prevent misuse.

What should you do with expired metronidazole?

If you have metronidazole tablets, creams, or gels that are past their expiration date, the safest thing to do is properly dispose of them so they cannot be misused or accidentally taken.

Follow these steps to safely dispose of expired metronidazole:

  1. Check if your local pharmacy, health department, or community has a drug take-back program where expired meds can be safely discarded.
  2. If no take-back program is available, mix the expired metronidazole with an unappealing substance like used coffee grounds, dirt, or cat litter in a sealed plastic bag.
  3. Throw the sealed bag in your regular household trash. Scratch out any personal information on the medication packaging.
  4. Never flush expired metronidazole down the toilet or drain unless specifically instructed to do so.

Once you have safely discarded your expired metronidazole, obtain a new prescription from your doctor if you still need antibiotic treatment for an active infection. Never take expired metronidazole pills or use creams, even if you still have symptoms.

Can you get a new prescription for expired metronidazole?

If you have an expired prescription for metronidazole that you were previously taking to treat an infection, you will need to consult your doctor again to get a new, non-expired prescription.

Your doctor may have you come in for an appointment to re-evaluate your condition. They will want to confirm you still have an active bacterial or parasitic infection that requires antibiotic treatment.

Be sure to inform your doctor:
– You have expired metronidazole that you need replaced
– What condition you originally took the metronidazole for
– When your symptoms started and if they have improved or worsened
– If you have taken any of the expired metronidazole medication

Your doctor will examine you and determine if a new prescription for non-expired metronidazole is appropriate. If your infection has resolved, they may not prescribe more metronidazole. But if you still need antimicrobial treatment, your physician can provide a fresh metronidazole prescription.

Always properly dispose of expired metronidazole instead of trying to use it or save it. Follow your doctor’s instructions if you need more prescribed after yours expires.

Is it bad to take expired metronidazole while pregnant?

Yes, it is particularly important for pregnant women to avoid taking expired metronidazole.

When used as prescribed by a doctor, metronidazole is generally considered safe during pregnancy. But taking expired metronidazole while pregnant could pose risks including:

  • Not fully treating bacterial vaginosis, increasing risk of preterm birth
  • Pregnancy complications if parasitic infections are not properly treated
  • Potential developmental issues in the fetus if degraded metronidazole crosses the placenta
  • Higher chance of side effects from chemical instability

Active infections during pregnancy need effective treatment, and expired medications may not provide proper microbial coverage.

Always talk to your obstetrician before taking any medications while pregnant, including metronidazole. Do not take expired metronidazole during pregnancy even if you still have symptoms of infection. Get a new prescription from your doctor for non-expired metronidazole if antimicrobial treatment is still needed.

Can expired metronidazole cause cancer?

There is no evidence that taking expired metronidazole causes cancer or increases cancer risk. When used as prescribed, metronidazole is typically safe in non-pregnant adults.

However, very high lifetime doses of metronidazole have been associated with some cancers in rodent studies. Chemical changes in expired metronidazole could hypothetically increase cancer risk at very high exposures.

Overall, the cancer risk from short-term use of expired metronidazole is extremely low. But it is still smart to avoid taking expired metronidazole if possible due to lack of effectiveness and other potential adverse effects.

Talk to your doctor if you have concerns about medications during cancer treatment. Do not take expired metronidazole without medical guidance. Seek professional advice if you develop unusual symptoms after taking expired metronidazole.

Can I take expired metronidazole for my dog or cat?

You should not give expired metronidazole meant for human use to your pets without veterinary approval.

Metronidazole is sometimes prescribed by vets for dogs, cats, and other animals to treat certain conditions like diarrhea, inflammatory bowel disease, or parasitic infections. But pet medication doses differ from human doses.

Giving your pet expired metronidazole meant for humans can be unsafe. Potential risks include:

  • Incorrect dosing leading to toxicity or lack of efficacy in pets
  • Greater risk of neurotoxicity in some animals
  • Lack of proper veterinary monitoring for side effects
  • Treatment failure if degraded medication does not properly treat the pet’s infection

Do not give your pets expired metronidazole or any other human medications without first consulting your veterinarian. Only give pets drugs prescribed specifically for them at the proper veterinary dose.


In most cases, it is not recommended to take expired metronidazole. Metronidazole is an antibiotic that can start to degrade after its printed expiration date. Taking expired metronidazole may fail to properly treat bacterial or parasitic infections. It can also potentially cause side effects or toxicity if degraded chemical compounds form.

Always discard expired metronidazole products so they cannot be taken accidentally. If you need more metronidazole to treat an active infection, consult your physician for a new prescription for non-expired medication. Never take expired antibiotics like metronidazole unless specifically instructed to do so by a medical professional. Appropriate storage and use of non-expired medications can help avoid risks and ensure you receive effective treatment.

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