Melatonin is a hormone that the pineal gland in the brain produces. Melatonin fulfills many functions in the body but it is mostly known for maintaining a circadian rhythm that is governed by the central circadian pacemaker (biological clock) in the suprachiasmatic nuclei in the hypothalamus. Melatonin works by attaching to receptors or nerve endings in the suprachiasmatic nucleus (SCN) in the hypothalamus. It binds to melatonin receptor 1 and melatonin receptor 2, commonly referred to as MT1 and MT2. People can take it as a natural or synthetic supplement to promote restful sleep. Melatonin showed promise for preventing shifts in sleep and wake times in people with jetlag and improving sleep in people with insomnia. It can also be used for headaches, cancer, and Alzheimer's disease.

Melatonin can be used as an analgesic, sedative, and hypnotic drug that can distinguish it as an attractive alternative premedicant

A study that was done before in J Anaesth by Borazan H et al revealed that postoperative pain score in patients undergoing radical prostatectomy who received melatonin one hour before surgery as a premedication was significantly lower than the control group with a significant P-value( less than 0.05).

The entropy is indicated for adult and pediatric patients older than 2 years intraoperatively for monitoring the electric state of the brain. In adult patients, state entropy and response entropy can be used as an aid in monitoring the effects of certain anaesthetic agents which will help the user to titrate the anaesthetic agent according to the individual needs of each patient.

Furthermore, the use of entropy parameters may be associated with a reduction of anaesthetic use and faster emergence of anaesthesia. The entropy measurement is to be used as an adjunct to other physiological parameters.

To the best of investigators knowledge, there is no study that examined the effect of melatonin on inhaled isoflurane requirements intraoperatively. So, in this study, the effect of melatonin will be assessed on intraoperative inhaled isoflurane requirements in patients undergoing open nephrectomy under general anaesthesia by using entropy

Inclusion Criteria:

• Patients undergoing nephrectomy under general anesthesia aged from 20 to 60 years.
• ASA 1 or 2.
• BMI 25 to 30

Exclusion Criteria:

• Patients with uncontrolled hypertension.
• Patients presenting with (IHD, significant arrhythmias, heart failure).
• Allergy to melatonin.
• History of epileptic seizures, psychoactive medications, neurological disorders or trauma.

Patients will be allocated to the study groups using a computer-generated random list, and the group assignments will be sealed in sequentially numbered opaque envelopes that will be opened before induction of anesthesia. The data collector will be blinded to the group assignment and to the monitoring anesthetist, and the person who will give the drug will not bethe data collector.