Medications That Cause Red Urine
Rifampin is the most clinically important medication that causes red-orange discoloration of urine and other body fluids, and patients must be counseled about this harmless but alarming side effect to prevent unnecessary concern and workup. 1
Primary Medications Causing Red Urine
Rifampin (Most Common)
- Rifampin colors urine, tears, sweat, and other body fluids orange-red 1
- This discoloration can permanently stain soft contact lenses, so patients should be advised accordingly 1
- The effect is harmless and expected, occurring through direct excretion of the drug in body fluids 1
- Patients should be counseled about this side effect before starting therapy to avoid unnecessary alarm 1
Phenazopyridine
- Causes reddish discoloration of urine, which is an expected therapeutic effect when used as a urinary analgesic 2
- This is a benign and anticipated side effect 2
Hydroxocobalamin
- Causes reddish discoloration of urine that mimics hematuria 2
- Clinicians should be aware of this common side effect to prevent unnecessary consultations and diagnostic workup 2
- This is particularly important as it can be mistaken for blood in the urine 2
Metronidazole
- Can cause reddish discoloration of urine, though this is a rare side effect 3
- The discoloration typically reverts to normal within 24 hours of discontinuing the medication 3
- This should be considered when no other obvious cause for urine discoloration is present 3
Mesalamine
- Causes red-brown urine discoloration, particularly after contact with sodium hypochlorite (bleach) in toilet water 4
- This reaction typically occurs after 2-3 days of use 4
- This is a harmless reaction that should be recognized to avoid unnecessary physical examination and patient worry 4
Additional Causes to Consider
Acetaminophen (in Overdose)
- Dark-brown urine can occur at an early stage of acetaminophen overdose 5
- This is caused by p-aminophenol excretion and may precede acute renal failure and hepatic dysfunction 5
- This represents a serious clinical situation requiring immediate intervention 5
Non-Medication Causes
- Foods such as beets and rhubarb can also cause red urine discoloration 2
- These benign dietary causes should be distinguished from medication effects and true hematuria 2
Clinical Pitfalls to Avoid
The key clinical challenge is distinguishing benign drug-induced urine discoloration from true hematuria, which requires different management approaches 2. When evaluating red urine:
- Always obtain a medication history including over-the-counter drugs and recent medication changes 3, 2
- Consider the timing of discoloration relative to medication initiation 3, 4
- Note whether discoloration occurs immediately upon voiding or after contact with toilet water/bleach 4
- Perform urinalysis to definitively rule out hematuria when the diagnosis is uncertain 2
- Be aware that topical medications containing azo dyes can also cause urine discoloration 6