Total body propofol clearance (TBPC) after living-donor liver transplantation (LDLT) surgery is decreased in patients with a long warm ischemic time

Pharmacokinetics of drugs in adult living donor liver transplant patients: regulatory factors and observations based on studies in animals and humans

INTRODUCTION

Limited information is available on the pharmacokinetics of drugs in the donors and recipients following adult living donor liver transplantation (LDLT). Given that both the donors and recipients receive multiple drug therapies, it is important to assess the pharmacokinetics of drugs used in these patients.

AREAS COVERED

Pathophysiological changes that occur post-surgery and regulatory factors that may influence pharmacokinetics of drugs, especially hepatic drug metabolism and transport in both LDLT donors and the recipients are discussed. Pharmacokinetic data in animals with partial hepatectomy are presented. Clinical pharmacokinetic data of certain drugs in LDLT recipients are further reviewed.

EXPERT OPINION

It takes up to six months for the liver volume to return to normal after LDLT surgery. In the LDLT recipients, drug exposure generally is higher with lower clearance during early period post-transplant; lower initial dosages of immunosuppressants are used than deceased donor liver transplant recipients during the first six months post-transplantation. In animals, the activities of hepatic drug metabolizing enzymes and transporters are known to be altered differentially during liver regeneration. Future studies on the actual hepatic function with reference to drug metabolism, drug transport, and biliary secretion in both LDLT donors and recipients are required.

Variability of standard liver volume estimation versus software-assisted total liver volume measurement

The estimation of the standard liver volume (SLV) is an important component of the evaluation of potential living liver donors and the surgical planning for resection for tumors. At least 16 different formulas for estimating SLV have been published in the worldwide literature. More recently, several proprietary software-assisted image postprocessing (SAIP) programs have been developed to provide accurate volume measurements based on the actual anatomy of a specific patient. Using SAIP, we measured SLV in 375 healthy potential liver donors and compared the results to SLV values that were estimated with the previously published formulas and each donor's demographic and anthropomorphic data. The percentage errors of the 16 SLV formulas versus SAIP varied by more than 59% (from -21.6% to +37.7%). One formula was not statistically different from SAIP with respect to the percentage error (-1.2%), and another formula was not statistically different with respect to the absolute liver volume (18 mL). More than 75% of the estimated SLV values produced by these 2 formulas had percentage errors within ±15%, and the formulas provided good predictions within acceptable agreement (±15%) on scatter plots. Because of the wide variability, care must be taken when a formula is being chosen for estimating SLV, but the 2 aforementioned formulas provided the most accurate results with our patient demographics.

The population pharmacokinetics of fentanyl in patients undergoing living-donor liver transplantation

Fentanyl, an opioid analgesic with a high hepatic extraction ratio, is frequently used to supplement general anesthesia during liver transplantation and is also continuously infused to provide postoperative analgesia. However, because fentanyl is metabolized mainly in the liver, the pharmacokinetics of fentanyl may vary widely during the different phases of the surgery, potentially leading to adverse events. Using nonlinear mixed-effects modeling, we characterized the pharmacokinetics of fentanyl in 15 patients (American Society of Anesthesiologists Physical Status Classification 2 or 3) undergoing living-donor liver transplantation (LDLT). Fentanyl was continuously infused at the rate of 200-400 µg/h throughout the operation. The time course of the fentanyl plasma concentration levels was best described in terms of a two-compartment model. Estimates were made of the pharmacokinetic parameters during the preanhepatic, anhepatic, and neohepatic phases: central volume of distribution (V(1)) (l): 59.0 + hourly volume infused by rapid infusion system (RIS) × 42.5, 113.0, and 189.0, respectively, × (body weight/69)(1.3); peripheral volume of distribution (V(2)) (l): 94.3, 412.0, and 427.0, respectively; intercompartmental clearance (Q) (l/h): 96.4 × (cardiac output (CO)/6.7)(2.5), 22.6, and 28.2, respectively; metabolic clearance (Cl) (l/h): 21.7 during the preanhepatic and neohepatic phases, and 0 during the anhepatic phase. The preanhepatic central volume of distribution was found to be markedly influenced by the massive infusion of fluids and blood products. The more hyperdynamic the circulation was during the preanhepatic phase, the higher the distributional clearance.