This medication is used to help relieve moderate to severe pain. Morphine belongs to a class of drugs known as opioid (narcotic) analgesics. It works in the brain to change how your body feels and responds to pain.

Opioid analgesics

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.

Oral- Moderate to severe pain: 5-20 mg 4 hrly. Extended-release: 5-20 mg 12 hrly. Dosage is dependent on the severity of pain.

Intraspinal- Moderate to severe pain: Initially, 5 mg epidural inj; after 1 hr, additional doses of 1-2 mg may be given up to a total dose of 10 mg/24 hr if pain relief is unsatisfactory. A dose of 20-30 mg daily may be required in some patients. Liposomal inj: 10-20 mg depending on the type of surgery.

Intrathecal- Moderate to severe pain: 0.2-1 mg once daily or 1-10 mg daily for patients with opioid tolerance. Some patients may require a dose of up to 20 mg daily.

Intravenous- Acute pulmonary oedema:

• Adult: 5-10 mg via slow inj at 2 mg/min.
• Elderly: Half of the usual adult dose.

Intravenous- Pain associated with myocardial infarction:

• Adult: 5-10 mg at 1-2 mg/min followed by a further 5-10 mg as necessary.
• Elderly: Half of the usual adult dose.

Parenteral- 

• Moderate to severe pain: 5-20 mg; 2.5-10 mg via slow IV inj over 4-5 min with patient in recumbent position or a starting dose of 1-2 mg/hr via continuous IV infusion (max: 100 mg/day; 4 g/day in cancer patients). Doses may be adjusted according to severity of pain and patient's response.
• Premedication in surgery: Up to 10 mg, given 60-90 min before operation.

May be taken with or without food. May be taken with meals to reduce GI discomfort.

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.

Renal Impairment: Dosage may need to be reduced.
Hepatic Impairment: Dosage may need to be reduced.

Symptoms: Resp depression, pinpoint pupils, extreme somnolence progressing to stupor and coma, skeletal muscle flaccidity, cold and clammy skin and sometimes bradycardia and hypotension. Apnoea, circulatory collapse, and cardiac arrest may occur in severe cases.

Management: Re-establish adequate resp exchange through provision of a patent airway and institution of assisted or controlled ventilation. Oxygen, IV fluid, vasopressors and other supportive measures may be employed as necessary. Naloxone may be given as antidote.

Inj/oral preparations: Store between 15-30°C. Liposomal inj: Store between 2-8°C. Supp: Store below 25°C. Protect from light.