Dark Yellow Urine During Metronidazole and Cefuroxime Treatment
Dark yellow to cola-colored urine while taking metronidazole is a benign, well-documented side effect caused by drug metabolites and requires no intervention—this is not a sign of infection, liver damage, or other pathology.
Understanding the Mechanism
Metronidazole causes urine discoloration in approximately 1 in 100,000 patients through excretion of a pigmented metabolite that has no clinical significance. 1
The color change typically ranges from dark yellow to brown or cola-colored and resolves completely when the medication is stopped, then recurs upon rechallenge. 2
This discoloration occurs without any adverse clinical effects—it does not indicate kidney damage, hemolysis, rhabdomyolysis, or drug toxicity. 2
Distinguishing Benign Discoloration from Pathology
The key differentiating feature is that metronidazole-induced discoloration occurs in isolation, without dysuria, fever, flank pain, or systemic symptoms. 3, 4
If you have no urinary symptoms (dysuria, frequency, urgency, fever >38.3°C, or gross hematuria) and no pyuria on urinalysis, this is simply drug-related pigment excretion. 5
Urinalysis will show normal findings except for color—no white blood cells, no bacteria, no protein, and no red blood cells beyond what might be seen from the pigment itself. 3, 4
When to Investigate Further
You should pursue additional workup only if:
New urinary symptoms develop (burning, frequency, urgency, suprapubic pain). 5
Fever >37.8°C, rigors, or systemic signs of infection appear. 6
The urine color persists beyond 48 hours after completing metronidazole. 2
You develop flank pain, nausea/vomiting, or signs suggesting pyelonephritis or obstruction. 6
Reassurance and Management
No treatment modification is needed—continue both metronidazole and cefuroxime as prescribed for the full course. 1, 2
The discoloration will resolve spontaneously within 24–48 hours after completing the metronidazole course. 2
Cefuroxime does not cause urine discoloration; the color change is attributable solely to metronidazole. 7, 8
Maintain adequate hydration, but understand that increased fluid intake will not prevent or reverse the discoloration—it is a metabolic byproduct, not a concentration effect. 3
Common Pitfalls to Avoid
Do not discontinue metronidazole based solely on urine color—this is a harmless side effect, not a reason to stop therapy. 2
Do not order unnecessary imaging (ultrasound, CT) or laboratory tests (liver enzymes, creatine kinase) for isolated urine discoloration without other symptoms. 2
Do not assume the discoloration indicates a urinary tract infection—UTI requires both urinary symptoms and pyuria (≥10 WBC/HPF or positive leukocyte esterase), not just abnormal urine color. 5
Do not confuse this benign finding with hematuria or myoglobinuria, which would be accompanied by positive dipstick results for blood and clinical context (trauma, muscle injury, hemolysis). 3, 4