PRINCIPLES OF USING ANALGESICS
The use of analgesics for the treatment of acute pain in patients with cancer is the same as for those not suffering from cancer. It is the treatment of chronic pain which is often poorly managed and requires a different approach.
The selection of which drug or drugs to use involves:
- selecting a drug appropriate for the type of pain
- selecting a drug appropriate for the severity of pain
- using combinations of drugs, not combined preparations
- following the analgesic ladder
- using adjuvant analgesics
- never using placebo
Drug selection depends upon the type and severity of the pain. Different types of pain respond to different analgesics. As it is important that pain be brought under control as quickly as possible, it is preferable to start with a stronger analgesic and subsequently wean the patient to a weaker drug.
When prescribing for patients with chronic pain, it is commonplace to use more than one drug. Different drugs should be given independently and compound preparations avoided because, if it is necessary to escalate the dose of one of the drugs, the dose of the second will also be increased and may cause unwanted toxicity.
If the prescribed analgesia is insufficient, or if the patient's disease progresses, analgesia is escalated in an orderly manner from non-opioid to weak opioid to strong opioid, as illustrated in the World Health Organisation's 'Analgesic Ladder'. Non-opioid analgesics should be continued when opioid drugs are commenced, as their action can be complementary and allow lesser doses of opioids to be used. Adjuvant analgesics should be used whenever indicated.
The analgesic drugs employed need not be numerous. The non-opioid drugs used are aspirin or a non-steroidal anti-inflammatory (NSAID) drug; codeine and oxycodone are the commonly used weak opioids and the strong opioid drug of choice is morphine.
There is no place for the use of placebo medications in the treatment of chronic pain due to cancer. It is unethical, will lead to distrust if discovered by the patient, and whether or not a response occurs provides no useful information.
The principles of analgesic administration for chronic cancer pain are:
- give in adequate dosage
- titrate the dose for each individual patient
- schedule administration according to drug pharmacology
- administer on a strict schedule to prevent pain, not PRN
- give written instructions for patients on multiple drugs
- give instructions for treatment of breakthrough pain
- warn of, and give treatment to prevent, side effects
- keep the analgesic program as simple as possible
- use the oral route wherever possible
- review and reassess
The selected drug or drugs are prescribed in a dose adequate to relieve the pain. A common failing is to give appropriate drugs but in inadequate doses. 'Standard' doses which are appropriate in the acute setting have no place in the treatment of chronic cancer-related pain and the dose needs to be titrated against the pain for each individual patient. Such individual titration of doses is necessary because differences in pain sensitivity between individuals and the considerable variation in the analgesic sensitivity of different pains result in a wide range of optimal doses.
The scheduling of drugs is according to the pharmacological properties and duration of clinical action. It is important that drugs are given according to a strict schedule, determined by the duration of clinical action, in order to prevent the recurrence of pain. Patients given doses that are too small or too infrequent may behave in a manner suggestive of psychological dependence, badgering the staff for extra doses of medication; this has been termed 'iatrogenic pseudo-addiction' and is resolved by the prescription of doses adequate in amount or frequency to provide continuous pain relief.
There is no place in the treatment of chronic cancer-related pain for giving analgesics on an 'as required' basis or pro re nata (PRN). As required or PRN orders invite inadequate treatment: staff may not enquire about pain and patients may not realise they have to ask for analgesics; staff or patients may minimise the number of doses for fear of addiction; or staff may be too busy to attend to requests, all of which result in unrelieved or recurrent pain.
Patients taking a number of different medications should be given written instructions to use at home. These should include the drug names, what each is for, which are to be taken regularly and which are to be taken for a particular indication such as nausea.
It is essential to give the patient instructions for the treatment of breakthrough pain. This is reassuring, avoids the despair which occurs if an analgesic program is ineffective and helps the patient feel in control of the situation.
Patients must be warned of possible side effects. For example, unless a patient is warned of the sedation which occurs transiently during the first few days of opioid therapy, the medication may not be taken. Similarly, treatment should be given to avoid preventable side effects, such as the prescription of laxatives when commencing opioid therapy. Fears about dependence and addiction may need to be discussed.
A patient's analgesic program should be kept as simple as possible. Too many patients are on multiple mild analgesics as well as multiple opioid drugs. It is usually possible to simplify the analgesic program, even for patients with severe pain.
The oral route should be used wherever possible. It has been repeatedly demonstrated that even severe pain can be well controlled with oral medication. Oral medication should only be abandoned if the patient is unable to take or retain medication given by this route.
Continued reassessment is required. A number of dose modifications are often required before optimal pain control is achieved and the inevitable progression of the disease also necessitates repeated reassessment and treatment alteration.
Multimodality and multidisciplinary treatment of pain
Analgesics are the cornerstone of the treatment of pain but they are only one modality of treatment. Optimal treatment:
- Frequently employs more than one therapeutic modality.
- Forms part of a multidisciplinary approach to care which includes the assessment and treatment of other aspects of suffering which may cause or aggravate pain.