Morphine is a phenanthrene derivative which acts mainly on the CNS and smooth muscles. It binds to opiate receptors in the CNS altering pain perception and response. Analgesia, euphoria and dependence are thought to be due to its action at the mu-1 receptors while resp depression and inhibition of intestinal movements are due to action at the mu-2 receptors. Spinal analgesia is mediated by morphine agonist action at the K receptor.
Additive depressant effects with other CNS depressants (e.g. sedatives, hypnotics, general anaesth, phenothiazines, other tranquilisers). May enhance the neuromuscular blocking action of skeletal muscle relaxants. Reduced analgesic effect with mixed agonist/antagonist opioid analgesics (e.g. pentazocine, nalbuphine, buprenorphine). Increased plasma concentrations with cimetidine. May reduce the efficacy of diuretics by inducing the release of antidiuretic hormone. May delay the absorption of mexiletine. May antagonise the GI effect of cisapride, domperidone and metoclopramide. May produce hyperpyrexia and CNS toxicity with dopaminergics.
Resp depression, obstructive airway disease, delayed gastric emptying, acute abdomen, heart failure secondary to chronic lung disease, known or suspected paralytic ileus, phaeochromocytoma. Concurrent admin with MAOIs or within 2 wk after treatment.
Nausea, vomiting, constipation, abdominal pain, dry mouth, anorexia, taste disturbance, dyspepsia, resp depression, sedation, dizziness, confusion, insomnia, headache, somnolence, involuntary muscle contractions, hyperhidrosis, rash, pruritus, asthenic conditions, HTN, bronchospasm, seizures, amenorrhoea, rhabdomyolysis, nystagmus.
Parenteral or oral: C, D (if prolonged use/high doses at term)
Patient with impaired resp function, severe bronchial asthma, convulsive disorders, acute alcoholism, delirium tremens, raised intracranial pressure, hypotension with hypovolaemia, cardiac arrhythmias, severe cor pulmonale, history of substance abuse, diseases of the biliary tract, pancreatitis, inflammatory bowel disorders, prostatic hypertrophy, adrenocortical insufficiency, toxic psychoses. Opioid dependent patients. Renal and hepatic impairment. Pregnancy and lactation.