Disclaimer: This article is intended solely for informational and educational purposes only. It does not constitute medical advice.
Sevoflurane is one of the most widely used volatile anesthetics in modern practice due to its low blood-gas solubility and rapid onset and offset. Most drugs encountered by patients are processed largely by the kidneys and liver. However, like other inhalational anesthetics, sevoflurane metabolism and elimination profile exhibits a relatively uncommon, in which only a small portion is metabolized, with the majority of the drug eliminated unchanged through breathing.
Sevoflurane metabolism involves oxidative defluorination in the liver, a process mediated predominantly by cytochrome P450 2E1 (CYP2E1). Pretreatment with disulfiram, a CYP2E1 inhibitor, reduced plasma fluoride and hexafluoroisopropanol (HFIP) production by 73–80%, substantially shortened the time to peak fluoride concentration, and diminished cumulative 96-hour urinary fluoride and HFIP excretion compared with controls. These findings established CYP2E1 as the principal, though not exclusive, enzymatic pathway for sevoflurane metabolism in humans (Kharasch et al., 1995).
The primary metabolites generated through this pathway are inorganic fluoride and HFIP, produced in an essentially 1:1 stoichiometric relationship (Kharasch et al., 1995a). Research demonstrated that HFIP was detectable in blood within five minutes of anesthetic initiation. HFIP circulated predominantly as a glucuronide conjugate, with unconjugated HFIP constituting 15% or less of the total.
Peak plasma fluoride concentrations averaged 36.2 μM, occurring roughly two hours after sevoflurane discontinuation, while peak HFIP concentrations occurred somewhat later, with a mean time-to-peak of 5.5 hours. Approximately 4.9–5.6% of the absorbed sevoflurane dose was metabolized overall, an estimate derived independently from both fluoride and HFIP excretion data and broadly consistent with earlier reports of 1–4% hepatic metabolism. The portion of sevoflurane that does not undergo metabolism instead undergoes elimination through the lungs, in which it is exhaled unchanged.
The clinical relevance of fluoride production has historically centered on comparisons with methoxyflurane, whose nephrotoxicity was linked to sustained plasma fluoride concentrations exceeding 50 μM (Kharasch et al., 1995a). While some sevoflurane studies have recorded peak fluoride levels above this threshold, a critical distinction is that methoxyflurane undergoes substantial intrarenal metabolism in addition to hepatic metabolism, a feature not shared by sevoflurane. This mechanistic difference likely explains why elevated fluoride exposure with sevoflurane has not translated into clinically meaningful renal impairment.
A large systematic review, which pooled data from 41 randomized-controlled trials encompassing more than 1,500 patients, reinforced this conclusion (Sondekoppam et al., 2020). Despite consistently higher peak and 24-hour fluoride concentrations with sevoflurane compared with alternative volatile agents, there were no significant differences in serum creatinine, blood urea nitrogen, or creatinine clearance at 24 postoperative hours.
These findings held across subgroups defined by FGF rate, anesthetic duration, absorbent type, and pre-existing renal dysfunction. Compound A, which has been found to be nephrotoxic in animal studies and is generated through the reaction of sevoflurane with alkaline carbon dioxide absorbents, showed an inverse relationship with FGF but no association with tubular or glomerular dysfunction in human studies.
Beyond the kidney, sevoflurane’s metabolic and physiologic profile may also confer organ-protective effects. A study in a rat model of hepatic ischemia-reperfusion injury found that sevoflurane preserved hepatic tissue blood flow, sustained ATP and energy charge, and reduced markers of oxidative and hepatocellular injury compared with isoflurane (Bedirli et al., 2008), suggesting that the metabolic handling of sevoflurane does not preclude, and may even support, favorable outcomes in vulnerable organ states.
Research has found that sevoflurane pharmacokinetics involve metabolism in the liver, but the majority of what is inhaled is exhaled in the same form. Additionally, while sevoflurane metabolism generates measurably higher fluoride and compound A exposure than alternative volatile agents, it has not been shown to translate into clinically significant renal dysfunction.
References
- Kharasch, E. D., Armstrong, A. S., Gunn, K., Artru, A., Cox, K., & Karol, M. D. (1995). Clinical sevoflurane metabolism and disposition. II. The role of cytochrome P450 2E1 in fluoride and hexafluoroisopropanol formation. Anesthesiology, 82(6), 1379–1388. https://pubmed.ncbi.nlm.nih.gov/7793653/
- Kharasch, E. D., Karol, M. D., Lanni, C., & Sawchuk, R. (1995a). Clinical sevoflurane metabolism and disposition. I. Sevoflurane and metabolite pharmacokinetics. Anesthesiology, 82(6), 1369–1378. https://pubmed.ncbi.nlm.nih.gov/7793652/
- Sondekoppam, R. V., Narsingani, K. H., Schimmel, T. A., McConnell, B. M., Buro, K., & Özelsel, T. J.-P. (2020). The impact of sevoflurane anesthesia on postoperative renal function: a systematic review and meta-analysis of randomized-controlled trials. Canadian Journal of Anesthesia, 67(11), 1595–1623. https://doi.org/10.1007/s12630-020-01791-5
- Bedirli, N., Ofluoglu, E., Kerem, M., Utebey, G., Alper, M., Yilmazer, D., Bedirli, A., Ozlu, O., & Pasaoglu, H. (2008). Hepatic energy metabolism and the differential protective effects of sevoflurane and isoflurane anesthesia in a rat hepatic ischemia-reperfusion injury model. Anesthesia & Analgesia, 106(3), 830–837. https://doi.org/10.1213/ane.0b013e3181616fc9
