Pain control in cancer patients

Overview:

• The symptom most feared by cancer patients is pain, although only 2/3 of patients suffer significant pain throughout the course of their disease
• Cancer is directly responsible for ~70% of the pain, the remainder being due to:
• Rapid weight loss
• Pressure sores
• Arthritis, etc

The analgesic ladder:

The cancer relief programme of the WHO groups drugs into 3 main classes:

1. Non-opioid drugs (e.g. paracetamol, NSAIDs)
2. Weak opioid drugs (e.g. codeine, dextropropoxyphene)
3. Strong opioid drugs (e.g. morphine and diamorphine)

The analgesic ladder states that, if optimal use of a drug from the non-opioid class (e.g. 1000mg of paracetamol TDS) does not result in satisfactory pain relief, the prescription should be increased up one step to a weak opioid. If the equivalent of codeine 60mg TDS is not sufficient to control pain, the patient will require a strong opioid

Strong opioid drugs:

Morphine is the drug of choice:

• In most circumstances, it should be given by mouth
• The dose can be tailored to the individual patient’s needs as morphine has no ceiling analgesic effect
• A suitable starting dose of morphine is 10mg qqh (or 5mg qqh if the patient is elderly or frail)
• Patients with renal failure will have impaired excretion of morphine metabolites; they should receive a single dose of morphine and be carefully observed for the return of pain in order to determine the approximate rate of excretion of the metabolites
• If a 10mg dose of morphine relieves the pain, but the relief does not last for 4 hours:
• A 50% increase in the dose should be made
• i.e. 10, 15, 20, 30, 45, 60, 90, 120, 180mg, until satisfactory pain control is achieved

When the patient’s 24-hour morphine requirement has been established, the prescription may be converted to a controlled-release preparation:

• There are now both 12-hour and 24-hour release preparations available
• The appropriate dose may be calculated by simple addition:

20mg morphine elixir qqh

= 120mg morphine per day

= 60mg bds of a 12-hour preparation or 120mg daily of a 24-hour preparation

If the patient is unable to take oral medication because of nausea/vomiting, GI obstruction or altering levels of consciousness, the opioid should be given either rectally or parenterally

Diamorphine is used for patients who need long-term analgesia:

• Has a greater solubility than morphine
• Given either SC or IM, diamorphine is ~2x as potent as oral morphine

Side-effects of the strong opioids:

Constipation is almost universal:

• The prescription of a stimulant laxative (e.g. co-danthrusate 1-3 capsules at night) should be mandatory
• No tolerance develops to this side-effect and laxative medication must be continued as long as analgesics are prescribed

Nausea and vomiting occurs in 30-60% of patients when first started on morphine:

• Tolerance will develop to this side-effect within 4-5 days

Confusion, nightmares and hallucinations:

• Occur in a small percentage of patients
• Tolerance to these side-effects does not develop
• A change of opiate drug is usually required

Pain not responsive to opioids:

• Not all cancer pains are relieved by opioids
• In some situations, the addition of co-analgesic drugs will result in improved pain control
• NSAIDs (e.g. naproxen 500mg bds) used in addition to a weak or strong opioid are good at relieving bone pain

Pains of nerve destruction (called dysaesthetic or deafferentation pain):

• Are generally only marginally improved by strong opiates
• Steroids have been found to be useful in reducing the symptoms
• In cases of constant burning dysaesthesia, the TCAs are helpful (e.g. amitriptyline 10mg at night, increasing incrementally to 75-100mg is usually sufficient)
• Anticonvulsant drugs are useful in the management of lancinating, neuropathic pains:
• Carbamazepine, starting at a dose of 100mg bds is most commonly used