Opioids-Clinical Use

Abstract

Morphine is a phenanthrene derivative. The effects are mediated by μ receptors. It is more effective for visceral pain and pain arising from deep structures and is less useful for superficial pain. It suppresses REM sleep and produces dysphoria and euphoria. Bradycardia and hypotension may be seen due to histamine release. It causes contraction of most sphincters except for the lower oesophageal sphincter which it relaxes. It has low lipid solubility and thus takes more time for its peak effect when given by the intramuscular route. It has a first-pass metabolism of 10–30 % via the oral route. Its half-life is 3–4 h. Dosage should be administered cautiously both in neonates (poor liver conjugating mechanisms) and elderly (decreased volume of distribution). It should be given cautiously in patients with liver and renal disease. It is metabolised by the gut wall and liver and morphine-3-glucuronide is the main metabolite. Another metabolite morphine-6-glucuronide is more potent than the drug itself.