EXAMINATION OF THE EFFECTS OF OBESITY ON THE PHARMACOKINETICS OF LONG-ACTING LOCAL ANESTHETICS IN THE RAT
Creators: Parvin, Shamima
Publisher: name: University of Alberta Library
Year: 2024

<p>Obesity has been a serious public health concern worldwide. Numerous significant drug-metabolizing enzymes have been shown to be altered (mostly down-regulated) in obesity. Surgery patients, including obese patients, are given long-acting local anesthetics such as ropivacaine and bupivacaine. A decrease in clearance can increase plasma concentrations of drugs, which can lead to an increased risk of adverse events. There is little available data on how obesity affects ropivacaine and bupivacaine pharmacokinetics. In our research project, our goal was to investigate the impact of obesity on pharmacokinetics of ropivacaine HCl and (±)-bupivacaine HCL. Bayesian forecasting can be used to estimate pharmacokinetic parameters (PKP) using sparse blood sampling. It is used clinically to find PKP in patients given drugs requiring concentration monitoring. We also examined the usefulness of Bayesian forecasting of sparse sampling to obtain pharmacokinetic parameters of those drugs. A new, sensitive reverse phase HPLC-UV assays were developed for ropivacaine HCl and its major metabolite N-despropyl ropivacaine (PPX). One-step liquid-liquid extraction was performed on 100 μL of rat plasma, and the residues were separated after the plasma was injected onto C18 analytical columns. The HPLC method was then used to characterize the in vivo microsomal study. For the microsomal study, male rats were given either a standard or high-fat diet (HFD) for fourteen weeks (n=4/group). Liver tissue was collected after a 14-week period. To obtain more sensitive assays, LC-MS was used to develop methods for ropivacaine and for enantiospecific bupivacaine measurement in rat plasma. A one-step liquid-liquid extraction was conducted on 100 μL of rat plasma, and the residues were separated after the plasma was injected onto C18 analytical columns and a chiral column for ropivacaine and bupivacaine, respectively. Those assays were used for pharmacokinetic studies after subcutaneous (SC) ropivacaine or (±)-bupivacaine administration in rats. For the rich sampling protocol jugular vein cannulated (JVC) rats (n=5) were injected 15 mg/kg ropivacaine HCl and on a separate group of JVC rats were administered 7.5 mg/ kg of (±)-bupivacaine HCl followed by removal of 9 and 10 blood samples respectively for ropivacaine and bupivacaine for a 12-hour period. Compartmental analysis was used to characterize the model and PKP. In the same group of rats, the same dose of ropivacaine HCl and a 5mg/kg dose of (±)-bupivacaine was given as a SC injection on each of two days, 7 days apart, and1-3 samples per rat taken on a randomly applied preset schedule up to 10 hours post-dose. To determine the effect of obesity, male and female rats (n=5 per group) were fed a high-fat diet (HF) and regular chow for 14 weeks. One or two blood samples were collected from each rat after 10 mg/kg and 5 mg/kg dose of ropivacaine and (±)-bupivacaine respectively. All plasma samples were assayed for ropivacaine using an achiral method and racemic bupivacaine enantiomers using stereospecific LC-MS. The PKP were estimated using a Bayesian forecasting program.The peak area ratios and plasma concentrations in both techniques showed linear correlations. Based on 100 μL of rat plasma, the lower limit of quantification for HPLC-UV were 35 ng/mL for ropivacaine and PPX. The lower limits of quantification using LC-MS were 5 ng/mL and 2.5 ng/mL for ropivacaine and each bupivacaine enantiomer, respectively. Ropivacaine, d-bupivacaine and l-bupivacaine follow a one compartmental model. From the rich sampling the CL/F and MRT was found 4.34±0.38 L/kg and 2.47±0.34 h for ropivacaine, respectively. The corresponding data for d-and l-bupivacaine after racemate were 3.92±0.82 L/kg and 3.22±0.85 h; and 3.78±0.79 L/Kg and 3.29±0.87 h, no significant difference was found when a Bayesian dataset was validated with the rich dataset. The effect of HFD was clear in with ropivacaine, with decreased CL in male rats. Changes in CL in the HFD rats matched the in vitro metabolism or ropivacaine to PPX. No apparent effects of age or sex were found with bupivacaine. Bupivacaine displayed modest stereoselectivity in its PKP. Bupivacaine PK appear to differ between older and younger adult rats. There was no significant impact of diet or sex on the PK of bupivacaine enantiomers. Since sparse sampling and Bayesian forecasting was shown to provide pharmacokinetic data, the same rats could be used for more than one experimental dosing of drugs. </p>