Can Cyanokit (hydroxocobalamin) cause urine to appear red or brown?

Hydroxocobalamin (Cyanokit) Causes Red Discoloration of Urine

Yes, Cyanokit (hydroxocobalamin) definitely causes urine to appear red or brown, which can mimic hematuria but is actually a benign and expected side effect of the medication.

Mechanism and Appearance

Hydroxocobalamin is a precursor of vitamin B12 with a distinctive dark red color. When administered for cyanide poisoning:

• The red color of hydroxocobalamin causes red discoloration of urine (chromaturia) 1, 2
• This discoloration can range from red to dark red to purple 3
• The effect is commonly mistaken for hematuria (blood in urine) 2

Clinical Significance

This side effect has important clinical implications:

• The red discoloration is explicitly mentioned in treatment guidelines as an expected effect 1
• It is a benign finding that requires no treatment 3
• The discoloration is temporary but can persist for several weeks after administration 3
• Understanding this effect prevents unnecessary diagnostic workups for suspected hematuria 2

Documentation in Guidelines

Multiple authoritative guidelines specifically mention this side effect:

• The American Heart Association guidelines (2023) recognize hydroxocobalamin as the primary recommended treatment for cyanide poisoning 4
• Expert consensus guidelines for stocking antidotes explicitly note: "Red color of drug causes laboratory test interference, red discoloration of skin and urine" 4
• Clinical practice guidelines emphasize that chromaturia is among the most common adverse effects 1, 5

Clinical Studies Confirming This Effect

Research studies have documented this phenomenon:

• A prospective study of hydroxocobalamin for cyanide poisoning identified chromaturia as the most frequently reported adverse event 5
• Case reports specifically describe "red-coloured urine without haematuria" following hydroxocobalamin administration 6
• A 2025 case report described "purple chromaturia" that persisted for five weeks after hydroxocobalamin treatment 3

Differential Diagnosis

When red urine is observed after hydroxocobalamin administration:

• True hematuria should be ruled out with appropriate testing
• Other causes of red urine include foods (beets, rhubarb) and medications (rifampin, phenazopyridine) 2
• Laboratory interference from hydroxocobalamin can affect urinary tests and hemodialysis equipment 7

Clinical Pearls

• The red discoloration of urine is expected and should not cause alarm
• Documentation in the medical record that this is an expected effect of hydroxocobalamin can prevent unnecessary consultations
• The effect is self-limiting and will resolve without intervention
• This side effect should not deter the use of hydroxocobalamin when indicated for cyanide poisoning

Understanding this characteristic side effect of hydroxocobalamin is essential for clinicians to provide appropriate reassurance to patients and avoid unnecessary diagnostic testing.