Analgesic Efficacy of Duloxetine in Patients Undergoing Lumbar Discectomy

The investigator will give the patients duloxetine capsule 60 mg orally before operation (skin incision) and anesthetize them with general anesthesia, then the investigator will test the postoperative analgesic efficacy in the form of 24 h analgesic consumption

Patients will receive single oral dose of placebo capsule, 2 hours before operation and will be anesthetized with general anesthesia that includes, Induction of anesthesia will be done by intravenous fentanyl, 2 µg / kg and propofol 1 - 2 mg / kg. Endotracheal intubation will be achieved by cis-atracurium, 0.15 mg / kg. Maintenance of anesthesia will be done by isoflurane and cis-atracurium, 0.03 mg / kg on demand. Additional intraoperative analgesia will be consisted of administration of intravenous boluses of fentanyl, 50 µg according to the attending anesthesiologist's decision. At the end of surgery, muscle relaxation was reversed using neostigmine 0.05 mg / kg and atropine 0.01 mg / kg