Injectable morphine is an acute treatment for major cancer pain, before any localised treatment is performed or when oral morphine is not efficient.
There are many pharmaceutical presentations of morphine chlorhydrate (with or without hydration) with various titers: 1%, 2%, 4%, with or without a conservative medium.
1 ml of a 1% solution gives 10 mg of morphine, 10 ml: 100 mg.
Peridural, intrathecal and intraventricular administration requires preservative-free morphine and filtration through a 0.22 μm filter.
Intramuscular injections are not advisable since they are painful and do not bring any kinetic improvement compared to subcutaneous administration.
Actions
Morphine is a potent dose-dependant analgesic.
It also acts on psychomotor behaviour and provokes either sedation or excitation.
With therapeutic dosages, morphine also has a depressing action of respiratory and cough centres. Respiratory depression progressively lessens with chronic administration.
Morphine often has an emetic effect either by direct action on vomiting brain stem centres or by stimulation of gastric emptying.
Morphine is responsible for myosis of central origin.
Morphine lowers tonus and peristaltism of longitudinal unstriated muscular fibres and increases the tonus of circular fibres. A sphincter spasm may therefore occur (pylorus, ileocaecal valve, anal sphincter, sphincter of Oddi, vesical sphincter).
As an indication (since all patients react differently), a general comparison can be made in terms of dosage and equivalent pain analgesia.
| Per os | Subcutaneous | Intramuscular | Peridural | Intrathecal |
| 1 mg | about 1/2 mg | about 1/3 mg | 1/10 to 1/20 mg | 1/50 to 1/200 mg |
In adult patients, morphine is generally initiated in 1 mg intravenous injections repeated every quarter of an hour until sedation (titration). Then further administration is performed:
either in subcutaneous injections of 5 to 10 mg, 4 to 6 times per day
or by self-controlled analgesia with morphine bolus controlled both by dosage and time between bolus.
For cancer patients with chronic pain, in oral morphine naive patients, the first daily dosage is generally 0.5 mg/kg/j (or appr. 30 mg/day), with continuous infusion (rather than iterative injections every 4 to 6 hours).
In patients already treated with oral morphine, the initial intravenous dosage should be approximately half of the oral dosage. However, if oral morphine is not efficient enough, a higher dosage may be prescribed.
In children, morphine is as indicated as it is in adults for treating pain, however dosage requires special precautions and competence.
The following contraindications are well known:
Decompensated respiratory insufficiency (when no ventilation device is available)
Severe cellular liver insufficiency (with encephalopathy)
Head injury and intracranial hypertension when no ventilation device is available
Uncontrolled severe epilepsy
Association with other morphine like drugs (like buprenorphine, nalbuphin or pentazocine): increased respiratory risks
The major and most frequently observed side effects are as follows:
constipation which never spontaneously regresses and should be systematically treated. Corrective therapy should always accompany morphine prescription (systematical laxative therapy).
sleepiness which, on the contrary, is generally transitory (except in the case of other associated pathologies)
nausea and vomiting are also transitory: their persistance should lead to investigation of another associated pathology.
Other frequent side effects:
confusion, sedation or excitation, with nightmares, especially in elderly patients, with possible hallucinations, a source of great anxiety for the patient (this neurotoxicity requires hydration and, if necessary, haloperidol treatment).
respiratory depression which can lead to apnea,
increased intracranial pressure (noticeably in case of a brain tumour), which should be prevented before instituting morphine treatment
dysuria or urinary retention, when prostatic adenoma or ureteral stenosis is associated to cancer,
pruritus and redness (mainly with intrathecal or peridural administration)
After persisting somnolence (a very precocious warning symptom) and respiratory depression, other symptoms appear: exceedingly closed myosis, arterial hypotension, general hypothermia and coma.
Treatment is an emergency:
Stopping morphine,
Assisted or stimulated ventilation or cardiorespiratory rehabilitation in specialised unit,
Specific treatment with naloxone (flash pain reappearance).
A withdrawal syndrome may occur when morphine is suddenly stopped.
The main symptoms are:
yawning, anxiety,
major irritability, diffuse myalgia with no precise location, arthralgia,
persisting insomnia,
shivering,
bilateral midriasis,
hot flushes, hypersudation
lacrimation and rhinorrhea,
nausea and vomiting with anorexia, abdominal cramps, diarrhoea.
Morphine is a level III analgesic on the WHO ladder.
In many countries (in France for example), morphine prescription is subject to specific legal guidelines.