All obese patients with a BMI ≥ 40 kg/m2 undergoing endoscopic gastric bypass surgery who receive a prophylactic single dose of 100 mg anidulafungin will be included in the analysis. A PK curve will be determined after administration of anidulafungin at t=0.5, 1, end of infusion, 2, 4, 6, 8, 10, 12, 24, and 48 and (if feasible) 72 hours post infusion (n=12 samples). Blood samples (4 mL) on PK days will be taken to obtain at least 2.0 mL of plasma.