MORPHINE

1) Action

• Narcotic analgesic

2) Mechanism

• Act on narcotic receptors in CNS

• Shares properties of naturally occurring enkephalins & endorphins

• Exert effect on CNS in 2 ways:

1) Reduce ability of patient to perceive sensation

2) Alter emotional reaction to sensation so that it is no longer perceived as pain

3) Indications

• Large doses may be used to achieve anaesthesia due its sedative, anxiolytic and analgesic properties [particularly in patients undergoing cardiac surgery when circulatory reserve is minimal]

• Severe pain

4) Effects on organs—side effects

• Respiratory depression

• Nausea & vomiting

• Cardiovascular depression

• Suppression of cough reflexes

5) Toxic effects/ precautions with administration

• Caution when given to patients on MAO inhibitors

6) Contraindications

• Head injuries [resp depression —> CO2 retention]

• Impaired respiratory or hepatic function

7) Reversal, antagonism or antidote

• Reversal with naloxane

8) Loading dose, maintenance dose, frequency & method of administration

• 1-3 mg/kg [high dose as adjunct to cardiac anaesthesia]

• For analgesia: regular IV small injections or a continual infusion

9) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Elimination half life: 3 hr

• % plasma protein binding: 35