Morphine
Mechanism :
Morphine, a pure opioid agonist, is relatively selective for the mu receptor, although it can interact with other opioid receptors at higher doses. In addition to analgesia, the widely diverse effects of morphine include drowsiness, changes in mood, respiratory depression, decreased gastrointestinal motility, nausea, vomiting and alterations of the endocrine and autonomic nervous system.
Indication :
- Pain-acute/post and peri-operative
- Sedation in ICU
- Chronic pain
- Palliative care
- Cyanotic spell
Contraindications :
Contraindicated in patients with known hypersensitivity to morphine, morphine salts, or any components of the product, in patients with respiratory depression in the absence of resuscitative equipment, in patients with acute or severe bronchial asthma and in any patient, who has or is suspected of having paralytic ileus.
Dosing :
Analgesia, Cyanotic spell: IM/IV/SC
Neonates: 0.3-1.2 mg/kg/day divided every 4 hours or continuous infusion 0.005-0.03 mg/kg/hour.
Infants and children <12 years: 0.05-0.2 mg/kg/dose every 2-4 hours or oral: 0.2-0.4 mg/kg/dose every 4-6 hours.
>12 years: 3-4 mg IV. May repeat after 5 min if required.
Postoperative pain:
0.01-0.04 mg/kg/hour by IV infusion.
Sickle cell disease, cancer pain:
0.04-0.07 mg/kg/hour by IV infusion.
Adverse Effect :
Respiratory depression, apnoea, vomiting, nausea, death, dehydration, dyspnea, sepsis, circulatory depression, shock, cardiac arrest, pruritus, urinary retention, headache, somnolence.
Interaction :
CNS Depressants: The concurrent use of other central nervous system (CNS) depressants including sedatives, hypnotics, general anesthetics, antiemetics, phenothiazines, or other tranquilizers or alcohol increases the risk of respiratory depression, hypotension, profound sedation, or coma.
Muscle Relaxants: Morphine may enhance the neuromuscular blocking action of skeletal muscle relaxants and produce an increased degree of respiratory depression.
Mixed Agonist/Antagonist Opioid Analgesics: Mixed agonist/antagonist analgesics (i.e. pentazocine, nalbuphine and butorphanol) should not be administered to patients who have received or are receiving a course of therapy with a pure opioid agonist analgesic. In these patients, mixed agonist/antagonist analgesics may reduce the analgesic effect and/or may precipitate withdrawal symptoms.
Monoamine Oxidase Inhibitors (MAOIs): MAOIs markedly potentiate the action of morphine.
Cimetidine: Concomitant administration of morphine and cimetidine has been reported to precipitate apnea, confusion and muscle twitching.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
| 20-50 | 75% of normal dose |
| 10-20 | Use small doses, e.g. 2.5–5 mg and extended dosing intervals. Titrate according to response |
| <10 | Use small doses, e.g. 1.25–2.5 mg and extended dosing intervals. Titrate according to response |
Dose in Patients undergoing Renal Replacement Therapies
| CAPD | Not dialysed. Dose as in GFR<10 mL/min |
| HD | Dialysed – active metabolite removed significantly. Dose as in GFR<10 mL/min |
| HDF/High flux | Dialysed – active metabolite removed significantly. Dose as in GFR<10 mL/min |
| CAV/VVHD | Dialysed. Dose as in GFR=10– 20 mL/min |
Hepatic Dose :
Mild and moderate hepatic impairment: Begin with a lower dose and titrate slowly while monitoring for sedation, respiratory depression and hypotension.
Severe hepatic impairment: Use is contraindicated as it can precipitate coma.
Morphine sulfate extended-release liposome injection, which is only used as a single epidural dose can be given without dose adjustment in hepatic impairment.