Morphine

How it works

It is an agonist at mu-opioid receptors in the central nervous system, modulating ascending pain transmission and the perception of pain.

Prescribing in practice

• Morphine causes dose-dependent respiratory depression and sedation, so titrate carefully, observe the patient, and have naloxone available, particularly with parenteral use or in the opioid-naive.
• Reduce dose and extend intervals in renal impairment, as active metabolites accumulate and prolong effects — relevant given obstructive uropathy can impair renal function.
• It is constipating and has dependence potential, so co-prescribe a laxative and review duration of use.

Monitoring

Monitor pain control, respiratory rate, sedation level and blood pressure, with bowel function over continued use.

Counselling the patient

• It may cause drowsiness; do not drive or operate machinery if affected and avoid alcohol.
• Constipation is common, so use the laxative provided; report severe drowsiness or slow breathing urgently.

Evidence & guidelines

Opioids including morphine are established for severe pain; in renal colic, NICE notes NSAIDs are first line with opioids used where NSAIDs are unsuitable or insufficient.