Which molecule is a competitive antagonist of pethidine?

Naloxone is recognized as a competitive antagonist of pethidine, which is an opioid analgesic. As an opioid, pethidine works by binding to opioid receptors in the brain to produce pain relief and other effects such as sedation. Naloxone, on the other hand, is specifically designed to bind to these opioid receptors and block their activation. This competitive antagonism effectively reverses the effects of opioid agonists like pethidine.

In emergency situations, naloxone is often used to counteract the life-threatening effects of opioid overdose, which can include respiratory depression, sedation, and decreased consciousness. By binding to the same receptors without activating them, naloxone can rapidly restore normal respiratory function and consciousness in individuals who have taken too much of an opioid.

The other options do not act as competitive antagonists to pethidine: Adrenaline is primarily involved in the 'fight or flight' response and does not interact with opioid receptors, Metoprolol is a beta-blocker used for cardiovascular issues and also does not involve opioid mechanisms, and Oestrogen is a hormone that has no antagonistic effects on pethidine. Thus, naloxone is the molecule that appropriately fits the definition of a competitive antagonist in this context