Obese patients with a BMI ≥ 35 kg/m2 undergoing endoscopic gastric bypass surgery will receive a 300 mg or 400mg dose of posaconazole. A PK curve will be determined after administration at t=0.45, 0.75, 1, 1.5, 2, 4, 8, 12, 24, and (if feasible) 48 hours post infusion. Blood samples (4 mL) on PK days will be taken to obtain at least 2.0 mL of plasma.