Green urine following a single induction dose of propofol

Dear Editor,

Propofol is widely used as an induction agent for general anesthesia and sedation in critical care units. Green urine with a single induction dose of propofol is rare, although it is often recorded after a prolonged infusion.[1,2,3]

A 48-year-old, 70 kg, American Society of Anesthesiologists physical status one male patient underwent bilateral modified mastectomy with axillary lymph node dissection under general anesthesia. The patient received tablet pantoprazole 40 mg as premedication. The intraoperative anesthetic drugs used were fentanyl 140 μg, propofol 140 mg, vecuronium 7 mg, nitrous oxide, isoflurane, neostigmine 2.5 mg, and glycopyrrolate 0.5 mg apart from 1.5 g of cefuroxime as antibiotic prophylaxis. The surgery took about 4 h. Recovery from anesthesia and extubation went uneventful. The patient reported voiding green urine 4 h later [Figure 1a]. Both the patient and treating physicians were quite alarmed by the green color. The patient was otherwise asymptomatic with stable vitals. Urine analysis and renal function tests were normal. There was no history of any previous anesthesia or similar discoloration with any drug in the past.

Figure 1.

(a) The color of urine on voiding eight hours after the administration of a single induction dose of propofol. (b) The fading green tinge 24 h later

Phenol-containing drugs (food coloring, amitriptyline, indomethacin, promethazine, cimetidine, etc.), dyes such as methylene blue and indigo carmine, and pseudomonas infection can cause urine to turn green. Other than propofol, we could not identify any other concomitant reasons for green urine in our patient.

A literature search revealed two previous reports of green urine following a single induction dose and it has never resulted in long-term consequences even in patients receiving a prolonged infusion.[1,2,3] The patient was reassured that it was benign and self-limiting. The greenish tinge decreased after 12 h and normalized in 36 h [Figure 1b]. The time of the appearance of green urine (2 h to 4 days) following initiation of propofol infusion as well as its disappearance after stopping infusion (2–24 h) is highly variable.[3] Except when secondary to infectious pathology, no intervention is needed.

Several causes have been proposed for the green urine following propofol. One reason is the phenol metabolites of propofol (such as 1-glucuronide, 4-glucuronide, and 4-sulfate conjugates of 2,6-diisopropyl-1,4-quinol) in urine.[4] Interindividual variability in hepatic and extrahepatic propofol elimination capacity has been suggested as another cause following prolonged infusion. Fujii-Abe et al.[2] analyzed both the green urine and the normal urine using liquid chromatography–mass spectrometry and observed two unique peaks in the green urine at 490 and 590 nm, the complementary colors being orange and blue. They assumed that the green color was observed because of a mixture of these two colors. While the exact cause has not been identified, the fading of the green color over time as in our patient indicates that the metabolite also decreased over time. Ku et al.[5] also report a dose-dependent alteration in the color of the urine. Green urine following propofol is not harmful. However, it remains to be ascertained if all individuals receiving propofol have a low concentration of the same metabolite.

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Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.