120 patients scheduled for ambulatory LC with general anesthesia were randomly assigned to three groups : group A received 40 mg parecoxib injection 30-45 min before anesthesia induction and 4 ml saline injection when gallbladder was removed ; group B received 4 ml saline injection 30-45 min before anesthesia induction and 40 mg parecoxib injection when gallbladder was removed ; group C received 4 ml saline injection 30-45 min before anesthesia induction and the time when gallbladder was removed .