Inclusion criteria:  Patients aged from 18 to40 years. ASA I-II. undergoing elective mega -liposuction surgery  BMI from 18 to 50 kg/m2  2. Exclusion criteria:  Patient refusal Contraindication or chronic use (consistent use for longer than 3 months) to any of the study drugs ASA III-IV. Patients aged less than 18 or more than 40. Body mass index >50. Suffered from severe psychiatric disease or drug addiction; Chronic opioid consumption, a history of regular sedatives or anticonvulsants intake, serious organ disease or dysfunction inability to use a PCA device History of parenteral or oral analgesic intake within the last 48hours.