Editor,

We read the article by Liang et al.1 with great interest. The authors conducted a multicentre, single-blind, randomised, parallel-group trial to investigate the efficacy and safety of ciprofol compared with propofol for the induction and maintenance of general anesthesia.1 Their conclusion stated that ciprofol was well tolerated, with a noninferior efficacy profile similar to propofol. We commend the authors for their valuable study, which contributes to our understanding of ciprofol as a potential alternative to propofol. However, we would like to report on a case of pink urine that we encountered in a patient who received ciprofol during anaesthesia induction. We believe this case warrants further consideration.

A 57-year-old man (W: 62 kg, H: 162 cm) with no previous significant medical history was admitted to the hospital due to sudden onset of abdominal pain. The patient was diagnosed with gastrointestinal perforation and scheduled for enteric perforation repair. Anaesthesia induction was performed using ciprofol at a dose of 0.4 mg kg-1. One hour after the induction, the patient excreted cloudy pink urine (Fig. 1a). Pink sediments precipitated in the urine on standing (Fig. 1b), and a polarising microscope revealed numerous uric acid crystals (Fig. 1c). The pink urine discoloration disappeared at the end of the operation. Several studies have extensively reported the incidence of pink urine syndrome associated with anaesthesia and surgical procedures involving propofol (2,6-diisopropylphenol).2 The mechanisms behind propofol-induced pink urine syndrome remain unclear. Propofol has been found to enhance uric acid excretion directly, resulting in the formation of uric acid crystals in the urine.3 We have presented for the first time the pink urine associated with ciprofol. Ciprofol, a novel 2,6-disubstituted phenol, is a chiral derivative of propofol. It is formed by introducing the ciprofol group as a stereocentre in the chemical structure of propofol, resulting in enantiomeric isomers. Ciprofol and propofol both contain a phenol group, which imparts some shared properties and chemical reactions that may be responsible for the disturbance of uric acid metabolism induced by ciprofol. The pink urine discoloration due to ciprofol is benign and self-limiting. A complete recovery without complications is anticipated. However, it is important to be aware of the risk of uric acid lithiasis.

Fig. 1:

(a) Pink urine in the urine collection bag 1 h after induction with ciprofol. (b) Pink sediments precipitated in the urine on standing. (c) Uric acid crystals under a polarising microscope.

Acknowledgements relating to this article

Assistance with the letter: none.

Financial support and sponsorship: the work was funded by the Qingdao Key Health Discipline Development Fund (QDZDZK2022094) and Qingdao Outstanding Health Professional Development Fund (2022).

Conflicts of interest: none.

Presentation: none.

This manuscript was handled by Dan Longrois.

References 1. Liang P, Dai M, Wang X, et al. Efficacy and safety of ciprofol vs. propofol for the induction and maintenance of general anaesthesia: a multicentre, single-blind, randomised, parallel-group, phase 3 clinical trial. Eur J Anaesthesiol 2023; 40:399–406. 2. Zhang F, Zhu X, Zhang H, et al. Case report: pink urine syndrome following exposure to propofol: a rare, impressive but benign complication. Front Pharmacol 2021; 12:686619. 3. Masuda A, Asahi T, Sakamaki M, et al. Uric acid excretion increases during propofol anesthesia. Anesth Analg 1997; 85:144–148.