The investigators designed a randomized double-blind placebo-controlled trial to evaluate the effect of preoperative single dose of oral melatonin and vitamin C administration on postoperative analgesia in patients undergoing elective major abdominal surgery.

The investigators designed a randomized double-blind placebo-controlled trial to evaluate the effect of preoperative single dose of oral melatonin and vitamin C administration on postoperative analgesia in patients undergoing elective major abdominal surgery. One hundred-sixty five ASA I-II adult patients between 18-65 years of age, undergoing elective major abdominal surgery with general anesthesia will be included in this double blinded, randomised, controlled study. Patients will randomly divided into equal (n=55) three groups. Preoperatively, one hour before surgery, patients will receive melatonin (6 mg) in group M, vitamin C (2 gr) in group C or placebo tablet in group P orally. A standard anesthetic protocol will be administered to all patients. At the end of surgery, postoperative pain control will be provided via a patient controlled analgesia (PCA) device including morphine in all groups. Hemodynamic parameters, pain, sedation, patient satisfaction, total morphine consumption, supplement analgesic requirement, incidence of nausea and vomiting and other side effects will be recorded at 5, 10, 30 min and 1, 2, 4, 6, 8, 12, 24 hr after surgery.

Inclusion Criteria:

Patients undergoing elective major abdominal surgery with general anesthesia

Exclusion Criteria:

A history of psychiatric disorders, chronic pain syndromes, obstructive sleep apnea, severe asthma, chronic obstructive pulmonary disease, congestive heart failure, hepatic or renal failure, patients with pregnancy or in lactation period or a history of allergic reaction to any drugs