Melatonin (N-acetyl-5-methoxytryptamine) is a neurohormone secreted by the pineal gland with several important functions, including regulation of the circadian rhythms, antioxidant and anti-inflammatory effects, accumulating evidence revealed that it also plays an important role in pain modulation through multiple mechanisms. The investigators aimed to evaluate the analgesic effect of enteral melatonin given 30 minutes before cannula insertion in preterm neonates by assessing Premature Infant pain Profile score (PIPP) before and 5 minutes after the procedure. Additionally, the study aimed to explore the relationship between procedural pain and oxidative stress, along with the effectiveness of pain management of melatonin by measuring Malondialdehyde (MDA), a well-accepted marker of oxidative stress, 60 minutes after the procedure.