Morphine
Class: analgesic β full opioid antagonist
Indications (NB some may be unlicensed): step 3 on the WHO ladder for severe pain, more effective in nociceptive than in neuropathic/visceral pains, severe breathlessness, intractable cough, diarrhoea
Contraindications/cautions: morphine hypersensitivity/allergy (not nausea/hallucination with opioids)
Adverse reactions: common: nausea/vomiting in 10 to 30% of patients (usually transient for 1 to 5 days) β give antiemetic, constipation in 90% of patients β give a stimulant & softener laxative prophylactically, dry mouth, dizziness, sedation (usually transient and on initiation or dose increase); less common: respiratory depression (high doses) β pain is an antidote β give naloxone if severe, visual problems β may see things upside down/ flipping, myoclonic jerking β sign of toxicity β try a different opioid, delirium in 2% of patients β give haloperidol; rare: hallucinations, hyperalgesia, raised intracranial pressure, biliary/urinary tract spasm, muscle rigidity, pruritus, pulmonary oedema, physical dependence (irrelevant in dying)
Metabolism/clearance: metabolised mainly in the liver by glucuronidation to active metabolites one of which is excreted by the kidneys so watch for accumulation in renal dysfunction; use alternative opioid
Interactions:
- additive CNS effects with other CNS depressants e.g. benzodiazepines (e.g. lorazepam), phenothiazines (e.g. chlorpromazine), tricyclic antidepressants (e.g. amitriptyline), other opioids
- faster onset of action of slow release morphine may occur with metoclopramide
| Dosing: | ||
|---|---|---|
| Pain (initially use the normal release and titrate to pain) | ||
| oral: | normal release | initially 5 to 10 mg 4 hourly and prn |
| slow release | initially 10 to 30 mg 12 hourly | |
|
||
| subcut: | oral:subcut = 2:1 | |
| rectal: | oral:rectal = 1:1 | |
| epidural: | subcut:epidural = 10:1 | |
| intrathecal: | subcut:intrathecal = 100:1 | |
| breathlessness, cough: | ||
| oral: | normal release 5 to 10 mg 4 hourly prn | |
Syringe driver: see syringe driver compatibility chart
Mechanism of action: stimulates mu (and other) opioid receptors in the CNS and gastrointestinal tract
Peak effect: oral: normal release 1 hour
Duration:
oral: normal release 4 to 5 hours oral: slow release 8 to 12 hours
Notes:
- tolerance to effect does occur but progressive disease is also a cause of dose fade
- if dose of slow release morphine is increased remember to also increase the prescribed dose of normal release morphine for breakthrough pain/rescue
- toxicity: decrease in respiratory rate, mental status and blood pressure β give naloxone (see naloxone page)
- for conversion to oxycodone, fentanyl or methadone, see relevant pages
- morphine can affect the ability to drive. Some patients may need to be told not to drive while taking morphine. Always advise patients not to drive for several days after a dose increase
- topical morphine may be useful for wound pain. It is usually used as 0.05 to 0.1% morphine (i.e. 0.5 to 1 mg/mL) in IntrasiteTM gel, metronidazole gel or KY JellyTM
- care with prescribing oral liquids β 1 mg/mL strength preferred. Be aware of strengths such as 10 mg/mL & potential for dosing errors
- SR capsules available in 10 mg, 30 mg, 60 mg & 100 mg; immediate release tablets 10 mg and 20 mg