Modified radical mastectomy may be associated with severe post-operative pain, leading to chronic pain syndrome which usually requires optimal perioperative pain management.

Patients will be randomly into two equal groups (40 patients each) according to the adjuvant added to the local anesthetic (bupivacaine) in the serratus anterior plane block using a computer-generated random numbers concealed in sealed opaque envelopes. Group B: The patients will receive 20 ml of 0.5% bupivacaine plus 5 ml 0.9% normal saline with total volume 25 ml. Group BM: The patients will receive 20 ml of 0.5% bupivacaine plus 150 mg magnesium sulphate in 0.9% normal saline with a total volume of 25 ml.

Inclusion Criteria:

• adult female patients
• American Society Of Anesthesiologists (ASA) class I or II
• scheduled for elective unilateral modified radical mastectomy

Exclusion Criteria

• patient refusal
• bilateral breast surgery
• coagulation disorders
• body mass index> 35
• allergy to local anaesthetics or magnesium sulphate
• severe respiratory or cardiac disorders
• pre-existing neurological deficits
• liver or renal insufficiency