Does Metronidazole (antibiotic) cause dark urine (hematuria)?

From the Guidelines

Metronidazole can cause dark or reddish-brown urine as a common side effect that is harmless and not a cause for concern. This discoloration occurs because the medication and its metabolites can change the color of urine as they are excreted by the kidneys. Patients should be reassured that this is an expected effect while taking metronidazole and will resolve once the medication is completed. However, if dark urine is accompanied by other symptoms like pain, fever, or jaundice, medical attention should be sought as these could indicate a more serious condition.

According to the guidelines for treating Clostridium difficile infection, metronidazole is no longer the first-line treatment due to its inferiority to vancomycin in clinical cure rates and resolution of diarrhea without recurrence 1. The standard treatment duration for metronidazole is 10 days, but extension to 14 days may be considered if symptoms have not fully resolved 1. It is essential to note that metronidazole should be used with caution, particularly for severe cases or when other treatments are available, due to reports of neurotoxicity with prolonged or repeated use 1.

Patients should complete their full course of metronidazole as prescribed, typically 7-14 days depending on the infection being treated, despite this side effect. Staying well-hydrated while taking metronidazole may help dilute the urine and make the discoloration less noticeable. The standard adult dose ranges from 250-500 mg taken 2-3 times daily, and the medication should be taken with food to minimize stomach upset. Key points to consider include:

• Metronidazole can cause dark urine as a harmless side effect
• The medication should be taken as prescribed, typically for 7-14 days
• Staying hydrated can help reduce the visibility of urine discoloration
• Metronidazole is no longer the first-line treatment for Clostridium difficile infection due to its inferiority to vancomycin 1

From the FDA Drug Label

Instances of darkened urine have been reported by approximately one patient in 100,000. Although the pigment which is probably responsible for this phenomenon has not been positively identified, it is almost certainly a metabolite of metronidazole and seems to have no clinical significance Metronidazole may cause dark urine in some patients, with an estimated incidence of approximately 1 in 100,000 patients. The cause of this phenomenon is thought to be a metabolite of metronidazole, and it is considered to have no clinical significance 2.

From the Research

Metronidazole and Dark Urine

• Metronidazole has been associated with urine discoloration, including dark or cola-colored urine, in some patients 3, 4.
• This side effect is considered rare and is not well-reported in the literature, but it can be a cause of concern for patients and clinicians 3, 4.
• Studies have shown that urine discoloration can occur in patients taking metronidazole for various infections, including Clostridium difficile sepsis and Steroid-resistant nephrotic syndrome 3, 4.
• The exact mechanism of metronidazole-induced urine discoloration is not well understood, but it is thought to be related to the drug's metabolism and excretion 3.
• In most cases, urine discoloration associated with metronidazole is reversible and resolves on its own after the drug is discontinued 3, 4.
• Clinicians should be aware of this potential side effect and provide reassurance to patients who develop abnormal urine color, as it is not typically associated with any clinically significant adverse outcomes 3.

Common Side Effects of Metronidazole

• Metronidazole is generally well-tolerated, but it can cause mild to moderate side effects, including nausea, abdominal pain, and diarrhea 5, 6.
• More serious side effects, such as neurotoxicity, optic neuropathy, and peripheral neuropathy, have been reported in rare cases 5.
• The frequency and duration of side effects associated with metronidazole can vary depending on the individual patient and the specific infection being treated 6.

Importance of Awareness and Monitoring

• Clinicians should be aware of the potential for urine discoloration and other side effects associated with metronidazole, and monitor patients closely for any adverse reactions 3, 4, 5, 6.
• Patients who develop abnormal urine color or other side effects should be reassured and closely monitored, as these effects are typically reversible and resolve on their own after the drug is discontinued 3, 4.