Why is this urine bag purple?

July 18, 2018

Figure 1 Quiz of the Week

An 80-year-old female with a history of diabetes and chronic constipation presents to the emergency department with a purple urine bag. She is currently bedridden and uses an indwelling catheter. On examination, she is hypotensive and confused. Blood cultures are positive for Proteus vulgaris.

Based on this patient’s presentation, which of the following antibiotics should be commenced?

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Image credit: @ctip.


Answer: Ciprofloxacin

This patient is presenting with urosepsis and purple urine bag syndrome—a rare complication of a urinary tract infection caused by the conversion of indoxyl sulphate into indigo, a blue-colored molecule, by certain Gram-negative bacteria. Given the presence of bacteremia, an intravenous antibiotic is appropriate. Since the choice of agent should be based on local resistance patterns, and because Proteus vulgaris is known to have inducible resistance to beta-lactam antibiotics, ciprofloxacin is the most appropriate option.

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