Green discoloration of urine after propofol infusion
A 32-year-old female patient had an emergency splenectomy after a traffic accident. Because of bilateral multiple rib fractures and accompanying bilateral hemothorax and pneumothorax, we decided to maintain prolonged mechanical ventilation after the surgery. A controlled mechanical ventilation mode was selected because of possible respiratory muscle fatigue and ventilator fighting. Appropriate sedation was achieved via continuous infusion of propofol at a rate of 3 mg/kg/h, with remifentanil at 2 mcg/kg/h. The patient's urine became yellowish green 19 hours after continuous propofol infusion (). Urinalysis revealed the following: pH, 6.0; urine SG, 1.015; bilirubin content, 1+; and urobilinogen level, 8.0 EU/dl. Urine culture was negative. As there were no signs of infection and no other known medication that could have discolored the urine, we suspected propofol as the cause. The urine color returned to normal 6 hours after discontinuation of propofol. The patient fully recovered after 2 weeks and was discharged from the ICU without further complications.\nThe main metabolic pathway of propofol is oxidation, reduction, and hydrolysis by cytochrome P450 and glucuronate conjugation in liver microsomes. Propofol exhibits a rapid distribution from the blood into tissue and a slow return from deep peripheral compartments back into the blood. Propofol is excreted in the urine after glucuroconjugation of the parent drug (to form the propofol-glucuronide) and sulfo- and glucuroconjugation of the hydroxylated metabolite to form 4-(2,6-diisopropyl-1,4-quinol)-sulphate, 1-, or 4-(2,6-diisopropyl-1,4)-glucuronide, respectively [,]. These quinol derivatives may be the cause of discoloration []. These derivatives do not reflect or alter renal function [].\nUrobilinogen, which is known to indicate liver parenchymal damage, was elevated in all 3 cases, as seen in previous reports [,]. This suggests that in a situation of dysfunction or functional decline of the liver, an extrahepatic pathway of propofol metabolism is augmented, resulting in the green coloration of the urine. As seen in case 1, changes in the pharmacokinetics may interfere with hepatic metabolism and may augment extrahepatic metabolism of propofol.\nThe total amount of infused propofol does not seem to be related to the induction of green urine (approximately 23500 mg in case 1, 4720 mg in case 2, and 2720 mg in case 3). Tan et al. [] reported that even injection with 100 mg of propofol, could cause green discoloration of the urine. The length of the administration period does not seem to be related either. While, Blakey and Hixson-Wallace [] reported that discoloration developed after 3 days of infusion, Tan et al. [] reported that the urine showed discoloration in 1 hour of propofol administration. In the present cases, green urine was shown after 6-64 hours of continuous infusion.\nIn conclusion, the green discoloration of urine was related to the circumstances facilitating extrahepatic metabolism, rather than the amount of propofol administered or the duration of administration. Although green urine associated with propofol is benign and rare, prompt recognition of such side effects is important in limiting medical expenditures, inordinate drug exposure, and distress among patients and clinicians [].