13.3 : オピオイド鎮痛剤: モルヒネおよびその他天然の同族種

Opioids are a diverse group of pain-relieving drugs categorized as natural, synthetic, or semisynthetic compounds.

Natural opioids, known as opiates, are alkaloids derived from the poppy plant.

Morphine, a benzylisoquinoline, possesses a complex three-dimensional pentacyclic structure with a distinct T-shaped X-ray conformation, enabling interaction with opioid receptors.

It binds strongly to the μ opioid receptor, triggering a cascade of reactions that relieve pain and induce euphoria.

Morphine has a linear pharmacokinetic profile and is rapidly distributed in the body tissues. In the liver, it conjugates with glucuronic acid to undergo renal excretion.

However, morphine can yield adverse effects, including nausea, miosis, drowsiness, constipation, respiratory depression, and cough reflex.

Codeine, a milder μ receptor agonist, is an analgesic and antitussive. However, it can cause respiratory depression and pose a risk of death in children.

Prolonged opiate use fosters tolerance, demanding higher doses for comparable effects, causing addiction, and culminating in withdrawal symptoms upon cessation.