Impact of Bariatric Surgery on Pharmacokinetic Study of Simvastatin and Carvedilol

Obesity, Bariatric Surgery, Roux-en Y Gastric Bypass

Bariatric surgery, Pharmacokinetics, RYGB, CYP2D6, CYP3A4

Obesity affects more than 1 in 3 adults in the U.S. It is commonly associated with reduced quality of life and complications such as metabolic syndrome, heart disease, high blood pressure and sleep disorders. The gastric bypass, also known as Roux-en-Y gastric bypass (RYGB), is one of the most common weight-loss surgeries due to the reliable and long-lasting weight loss and the effective remission of obesity-associated conditions. Although the impact of obesity on absorption, distribution, metabolism and excretion has been documented for several drugs, label recommendations might not account for specific population subgroups, specially morbidly obese patients and obese patients post-bariatric surgery. This study aims to investigate the impact of obesity and RYGB surgery on the kinetic disposition of simvastatin (Study A) and carvedilol (Study B).

The study is ongoing and eligible subjects are enrolled after signing a written informed consent. Research participants (n=120, in total) include healthy volunteers \[body mass index (BMI) ≤ 25 kg/m2\], obese \[BMI \> 30 kg/m2\] and patients that underwent RYGB surgery 6-60 month prior this research protocol. On day 1, participants receive a single oral dose of 40 mg simvastatin (Study A) or 25 mg racemic carvedilol (Study B). Serial blood samples are collected up to 24 h for the pharmacokinetic analysis. Blood tests (blood count, fasting blood glucose, lipid profile, serum creatinine, urea, gamma-glutamyl transferase, aspartate aminotransferase and alanine amino transferase) are being monitored for all enrolled participants. Blood samples are also collected for genotyping the main genetic polymorphisms associated with carvedilol or simvastatin pharmacokinetics. Metoprolol is being used as a probe drug for CYP2D6 in vivo phenotyping only for research participants enrolled in Study B. After oral administration of metoprolol (on day 2), urine samples are being collected up to 8h after drug administration to determine the urinary metabolic ratio α-hydroxy metoprolol/metoprolol. As part of the pre-surgery evaluation (obese group) or post-surgery follow-up (RYGB group), obese patients and patients post-RYGB are submitted to digestive endoscopies. Healthy participants will not undergo endoscopic examination. The preparation protocol for digestive endoscopy includes: a) 8-hour fasting; b) 10% spray lidocaine (topical); c) oral simethicone (75 mg/ml, 80 drops); d) oxygen therapy depending on the patient (nasal catheter with O2 at 3 L/min); e) 0.02 to 0.03 mg/kg intravenous midazolam; f) 50 mg pethidine. A blood sample is collected 4-h after intravenous midazolam for in vivo CYP3A4 phenotyping. During the endoscopies, duodenum and jejunum biopsies are being collected to investigated interindividual variability related to drug oral bioavailability (only obese and post-RYGB research participants). Samples collected from digestive biopsies will be used to develop individual enteroid microfluidic systems. In vivo phenotyping of drug metabolizing enzymes and transporters will also be assessed by transcriptome using blood samples. The generated in vitro and in vivo data will be combined to build up physiologically based pharmacokinetic models for precision dosing in obese and post-RYGB patients.

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