Does Metronidazole Cause Dark Urine?
In our latest question and answer, our pharmacist discusses how metronidazole can cause urine discoloration.
Hi. I was recently prescribed Flagyl 500mg 2x/day for a week. I have had this before and developed a persistent infection in my throat, so my doctor also gave me two doses of Diflucan as a precaution. I started the Flagyl Friday night. I took the first dose of Diflucan yesterday. The second I will take tomorrow. My concern is despite drinking plenty of water, my urine is super dark. Like a shade beyond apple juice. I also had the stomach flu this week (before and during this medication). I’m exhausted and have no energy, but that was true from the start of the flu, before the medicine. Should I stop taking the Flagyl? Do I need to see a doctor?
Sep 25, 2022- Metronidazole is well known to cause darkened urine, which is thought to be due to drug metabolites eliminated through the urine and is not considered clinically significant.
- Other urinary symptoms may also occur with metronidazole including painful urination, increased urinary frequency, and pelvic pressure.
- You should report any unusual or severe symptoms to your doctor, as dark urine can occasionally indicate more serious conditions like kidney or liver damage.
Answer
Flagyl (metronidazole) is well known to cause urine discoloration (darkened urine), so what you are experiencing is a possible side effect of the drug.
Why Does Metronidazole Cause Dark Urine?
It is unknown exactly why discoloration can occur. Elimination of metronidazole and its metabolites occurs mainly via the urine (over 60% of the dose) and it is thought that the occurrence of darkened urine is most likely due to a metabolite of the drug. There does not appear to be any clinical significance to this side effect.
The prescribing information for Flagyl ER (metronidazole extended-release) puts the incidence of urine discoloration at 3%, so it certainly isn't uncommon. If metronidazole is the reason in your case, there is no need to worry.
In addition to urine discoloration, metronidazole may cause other urinary symptoms as well. These could include painful urination, increased urinary frequency, and a sense of pelvic pressure.
Fluconazole isn't typically associated with darkened urine so metronidazole is most likely the culprit.
Other Considerations
Darkened urine is certainly a symptom of being dehydrated, but it doesn't necessarily mean that you are. As mentioned above, metronidazole may be the reason. As you also have the flu, it is important to stay hydrated and report any unusual or severe symptoms to your doctor.
It's also important to point out that dark urine is a fairly non-specific symptom. While the most common causes are dehydration and drugs (such as metronidazole in your case), it could be a symptom of something more serious (such as kidney or liver damage).
It's never a bad idea to talk to your doctor about what you are experiencing as they have your full medical history.
Final Words
Thanks so much for reaching out to us!
Glossary — Terms in This Answer
- Flagyl
- A brand name for the antibiotic medication metronidazole used to treat bacterial and parasitic infections.
- Metronidazole
- An antibiotic drug that kills bacteria and parasites and is commonly used to treat infections.
- Side effect
- An unintended and usually undesirable effect that occurs when taking a medication in addition to the intended therapeutic effect.
- Metabolites
- Chemical substances produced when the body breaks down and processes a drug.
- Elimination
- The process by which the body removes drugs and their breakdown products through urine, feces, or other means.
- Incidence
- The rate or frequency at which something occurs, often expressed as a percentage.
- Dehydrated
- A condition in which the body does not have enough water or fluids to function properly.
- Non-specific symptom
- A sign of illness that could be caused by many different conditions rather than one particular disease.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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