Morphine is a strong opioid and is the mainstay in the management of moderate to severe pain in patients with cancer. 80% of patients can obtain pain relief if morphine is prescribed appropriately for opioid responsive pain.

Morphine is on the 3rd Step of the WHO Analgesic Step Ladder and should be considered early when pain control is inadequate with NSAIDs and/or weak opioids.

Patients need not suffer unnecessarily from cancer pain. It can be controlled if the following MYTHS and MISCONCEPTIONS about morphine are dispelled.

1. Morphine causes addiction.
   Morphine DOES NOT cause addiction when used to control pain.

2. Morphine is used only as the last resort when the patient is terminally ill.
   Morphine can be used at ANY STAGE to control pain so that the patient may have a better quality of life.

3. Morphine should not be given more frequently than every 8 hours.
   Morphine should be given every 4 hours. This interval is increased only in elderly patients and/or the presence of severe liver and renal impairment.

4. There is a limit to the amount of morphine that one should prescribe.
   There is no upper limit to morphine dosage. The dose of morphine that should be prescribed is the dose that the patient requires to control pain.

The oral route should be the route of first choice. It has the bioavailability of about 30% of the parenteral dose. This means that three times the parenteral dose is required when morphine is given by the oral route.

Oral morphine is generally available in two forms:

• Morphine mixture or Aqueous morphine
  Usual concentration of 2 mg/ml (5ml = 10mg).
• Morphine Sulphate slow release tablets in 10mg, 30mg or 60mg.

General principles for morphine administration are:

1. By the mouth
2. By the clock
3. By the ladder
4. For the individual
5. Use adjuvant medications when necessary

Age	Starting Dose	Frequency
< 60 years 60 - 80 years	10mg 5mg	4 hourly 4 - 6 hourly
impaired renal function	depending on age as above	6 to 24 hourly
impaired liver function	depending on age as above	6 to 24 hourly

In elderly patients and in patients with liver and renal impairment, the dose and frequency can be adjusted to the duration of analgesia. In younger patients and in those with normal liver and renal function, morphine should be given BY THE CLOCK.

Break through pain is pain that recurs in between the regular doses of morphine and should be treated with additional (rescue) doses of morphine. The dose to be given is:

• regular dose, if pain returns in less than 2 hours
• half the dose, if more than 2 hours

• by 50%, if the dose is between 10mg - 40mg
• by 25%, if the dose is 40mg and above

When initiating morphine therapy, patients should be woken up for their midnight and early morning doses. Once the dose is stabilised, one and a half times (1.5x) the regular dose can be given just before retiring at night to enable patients get 6 hours of uninterrupted sleep.

The main aim of this regime is to:

Patients should be monitored regularly for the effectiveness of the analgesia and its side-effects, such as nausea, vomiting, sedation, respiratory depression, urinary retention and constipation.

Do not wait for the patient to complain of pain before you administer the next dose of morphine. There is no upper limit to the dose of morphine that can be prescribed. The end point is pain relief. There are, however, two situations when morphine may NOT be able to control pain even with large doses. They are:

• Neuropathic pain - when the tumour has involved the peripheral or central nervous system. This type of pain is characteristically burning or shooting in character.

• Pain due to pathological fracture - when the patient has severe pain on movement, with little or no pain at rest.

• NDSAIDs for bone pain from metastasis, unless contraindicated.
• Corticosteroids for pain of cord or nerve compressions.
  Dexamethasone 4 - 8 mg daily for 3 - 4 days.
• Anticonvulsants for neuropathic pain.

 
Transdermal Fentanyl

Fentanyl is a strong and potent opioid that is highly lipid soluble and is thus suitable for use by the transdermal route. It is particularly useful in chronic stable nociceptive pain, such as in patients who have difficulty swallowing due to oesophageal tumours or in patients with intestinal obstruction.

Fentanyl increases compliance as it can be applied to the skin and a single patch lasts 72 hours. Constipation is less with TTS fentanyl.

It is currently available in two strengths; 25 ug/hour and 50ug/hour.

As it is applied to the skin, it is difficult to titrate the drug to the intensity of the pain. Hence, it is always advisable to use aqueous morphine to achieve pain control before changing to TTS fentanyl.

It takes between 8 - 14 hours for serum levels of fentanyl to stabilise when a patch is first placed. During this period, morphine should be continued regularly. Thereafter, morphine should be available for break through pain. This is an important fact to remember.

Transdermal fentanyl is expensive.

 
See Also:
Management of Adverse Effects of Morphine