Morbid obesity (MO) is associated with several disorders such as hypertension, type 2 diabetes, dyslipemia and degenerative arthropathy that require pharmacological treatment. Drug bioavailability and metabolism in patients with MO is altered compared to population controls. Bariatric surgery is the gold standard treatment for MO when conventional therapy fails.

Bariatric surgery techniques can modify drug absorption in MO patients. These modifications depend on the drug absorption characteristics and on the bariatric surgery technique used. The changes in weight and body composition caused by BS at middle term can alter drug bioavailability and metabolism. The kinetics of the "normalization" process in patients with MO after bariatric surgery is unknown

Objectives. To analyze the changes in drug metabolism and pharmacokinetics. To establish drug dosing criteria in the post-intervention period in patients with MO after bariatric surgery. To determine the relationship between changes in drug bioavailability and metabolism in MO after bariatric surgery (longitudinal gastrectomy and Y-roux gastric by-pass).

Patients and methods. A prospective study of two cohorts of patients in a program of bariatric surgery (gastric by-pass and sleeve gastrectomy). Study "before and after".

Evaluations. Study on drug metabolism and pharmacokinetics using a modified "karolinska cocktail" (dextromethorphan, caffeine, losartan, omeprazole and paracetamol) before bariatric surgery and at 4 weeks and 6 months post-intervention.

Inclusion Criteria:

• Adults (from 18 to 55 years)
• Morbid Obesity BMI > 40 or BMI> 35 plus co-morbidity
• Healthy controls (non-overweight and overweight groups)

Exclusion Criteria:

• Allergy to study drugs
• Liver diseases