90 female patients scheduled for cancer breast surgeries will be assigned to 2 groups, each of 45. Group (K) will receive a bolus of 0.5 mg/kg ketamine with induction of anaesthesia, followed by ketamine infusion 0.12 mg/kg/hour continued till 24 hours after surgery. Group (KM) will receive a bolus of 0.5 mg/kg ketamine added to 50mg/kg magnesium sulfate over 30 minutes after induction of anaesthesia, followed by ketamine infusion 0.12 mg/kg/hour added to 8mg/kg/hour of magnesium sulfate continued till 24 hours after surgery. The same anaesthetic regimen will be applied to all patients. Total intraoperative fentanyl required to maintain mean blood pressure within 20% of its baseline will be recorded. After surgery, all patients will be connected to PCA device containing morphine solution, the amount of morphine consumed during the first 24 hours will be recorded. In the follow-up visits after 3 months, all patients will be assessed for neuropathic pain by DN4 questionnaire.

90 female patients aged between 18 and 65 years, scheduled for cancer breast surgeries will be assigned to 2 groups, each of 45. Group (K) will receive a bolus of 0.5 mg/kg ketamine with induction of anaesthesia, followed by ketamine infusion 0.12 mg/kg/hour continued till 24 hours after surgery. Group (KM) will receive a bolus of 0.5 mg/kg ketamine added to 50mg/kg magnesium sulfate over 30 minutes after induction of anaesthesia, followed by ketamine infusion 0.12 mg/kg/hour added to 8mg/kg/hour of magnesium sulfate continued till 24 hours after surgery. The same anaesthetic regimen will be applied to all patients. Total intraoperative fentanyl required to maintain mean blood pressure within 20% of its baseline will be recorded. After surgery, all patients will be connected to PCA device containing morphine solution, the amount of morphine consumed during the first 24 hours will be recorded. In the follow-up visits after 3 months, all patients will be assessed for neuropathic pain by DN4 questionnaire.

Inclusion Criteria:

• Patients with class II physical status (American Society of Anaesthesiologists) ,
• Age between 18-65 years,
• Scheduled for breast cancer surgery (e.g. modified radical mastectomy and conservative mastectomy)

Exclusion Criteria:

• Patient refusal,
• Cardiac dysfunction (ejection fraction <45%),
• Diabetic patients
• Patients with uncontrolled hypertension
• Patients have any degree of heart block
• Patients have renal impairment (creatinine > 2 mg/dl),
• Patients have hepatic dysfunction (transaminases > 2 times normal),
• Patients with preexisting neurological or psychiatric disease,
• Patients who are allergic to one of the study drugs,
• Patients with communication difficulties,
• Inability to use the patient controlled analgesia (PCA) device,
• Female patients who are pregnant
• Patients who use preoperative calcium channel blockers or narcotic drugs.

The study medications were prepared by a pharmacist who was not involved in the patient management or the data collection. Both the patients and the stuff involved in their management were unaware of the group assignment. Equal rates of the drug infusion and equal volumes of the administered drugs were applied to all patients to ensure double blinding of the study.