[(Science: drug) An opioid alkaloid, isolated from opium, with a complex ring structure. It is a powerful analgesic with important medical uses, but is highly addictive. functions by occupying the receptor sites for the natural neurotransmitter peptides, endorphins and enkephalins, but is stable to the peptidases that inactivate these compounds. pharmacologic action: narcotic analgesia, increases venous capacitance and reduces systemic vascular resistance. uses: analgesic for ischemic chest pain, hemodynamic changes lead to reduced pulmonary congestion, reduced myocardial oxygen demand. dose: 1-3 mg slow iV increments until desired effect. potential complications: respiratory depression, hypotension, especially in hypovolemic patients.
[1. The major phenanthrene alkaloid of opium; it produces a combination of depression and excitation in the central nervous system and some peripheral tissues; predominance of either central stimulation or depression depends on the species and dose; repeated administration leads to the development of tolerance, physical dependence, and (if abused) psychic dependence. Used as an analgesic, sedative, and anxiolytic.