Pharmacological management of chronic pain

For further information on the role of opioids in chronic pain see: Understanding the role of opioids in chronic non-malignant pain bpac^nz, October 2018

In this article

• Understanding pain
• Pharmacological treatment of pain
• References

In this article

Understanding pain

Pain is a common problem. Patients tell us if they have acute pain they are often vocal, upset and asking for help. In contrast, chronic pain is often hidden and unless we ask patients we may not find out they are in pain. The burden of chronic pain is in its impact on daily life.

“Think of pain as the fifth vital sign”

Managing pain includes helping the patient understand why they have pain, creating realistic expectations for relief and treating the pain.

Although not covered in this article, the psychological aspects of care are paramount. Factors such as anxiety and depression, which may reduce tolerance to pain or be exacerbated by pain, must also be assessed and treated.

There are two types of pain
From a practical point of view, pain is either generated by damage to the nerves (neuropathic pain), or by damage to other tissues (nociceptive pain). The anatomical source of the pain should be identified and this will then guide treatment. It is important to be aware that people can have more than one source or type of pain at one time.

The relationship between a painful stimulus and the experience of pain is extremely complex. Modification of the stimulus occurs in the peripheral and central nervous systems. The final perception of pain is strongly influenced by emotion and cognition.

Recognition of pain

Ask.

Diagnosis of pain

Ask more.

• How bad is the pain?
• Where is it? Does it go anywhere?
• What makes the pain worse? What makes it better?
• How is the pain described? e.g. dull, sharp
• How does it impact on daily life?

Signs of pain in people with communication difficulties¹

Pain scales can help to determine severity

Pain is what the patient says it is. It cannot be measured directly but pain scales may be used to assess severity. The most clinically useful pain scales include an assessment of impact on daily life.

An example of this is the Support Team Assessment Schedule (STAS) pain module²

Measurement of effect of pain on patient:

• 4 = Severe and continuous overwhelming pain. Unable to think of other matters.
• 3 = Severe pain often present. Activities and concentration markedly affected by pain.
• 2 = Moderate distress, occasional bad days, pain limits some activities.
• 1 = Occasional grumbling, single pain. Patient not bothered to be rid of symptom.
• 0 = None.

Scales can be made even more useful if they are personalised. For example, in the case of a patient with severe arthritis in their hip, level four could be continuous pain day and night with the patient being unable to sleep, level three could be the patient is able to sleep but is still troubled with pain while they are awake and so on. These scales can be used to set individual goals.

Other commonly used pain assessment tools include:³

• Numerical rating scale: pain is rated on a scale from 0 (no pain) to 10 (worst pain imaginable).
• Verbal rating scale: a four-point scale in which pain is rated as none, mild, moderate or severe.
• Visual analogue scale: an unmarked line with “no pain” at one end and “worst pain imaginable” at the other end.
• Faces pain scale: There are several versions available showing smiling or neutral faces for no pain and sad or crying faces indicative of severe pain.

So what is causing the pain?

In order to manage pain, work out which tissue the pain is coming from. At its simplest, this divides neuropathic pain from nociceptive pain. Nociceptive pain then needs to be diagnosed further using the same process as with any differential diagnosis.

For example, chest pain could be:

• Sharp and burning with associated allodynia (sensation of pain due to light touch). Diagnosis: neuropathic pain, query shingles.
• Pain worse on movement, tender to touch, associated with bruising. Diagnosis: nociceptive pain, soft tissue injury.
• Sharp pain worse on breathing, associated crackles on auscultation and fever. Diagnosis: nociceptive pain, pleurisy.
• Central, crushing pain, worse on exercise, associated dyspnoea. Diagnosis: nociceptive pain, ischaemia.
• Central, burning pain, worse after eating. Diagnosis: nociceptive pain, oesophageal irritation.
• Tight, hot, burning sensation localised around wound. Diagnosis: nociceptive pain, skin infection.

Pharmacological treatment of pain

Medications that may be considered for treating pain include drugs that treat specific conditions (adjuvants) and drugs in the analgesic ladder. There is one ladder for nociceptive pain (see below) and one for neuropathic pain.

Pain control is not always easy. It can be complicated by psychological and addiction problems. Adverse effects of medications may be problematic. Don’t hesitate to seek advice from a specialist.

The WHO analgesic ladder for nociceptive pain

The WHO analgesic ladder⁴ follows a simple step approach to pain management, starting with a non-opioid and moving up to potent opioids. It is important to be guided by the following rules:

• By the mouth – oral medication
• By the clock – regular medication
• By the ladder – use the analgesic ladder
• Individual dose titration – find the right dose for the patient
• Use adjuvant drugs – treat specific conditions
• Attention to detail – keep reviewing the diagnosis and check for adverse effects

Adjuvants are used at every step of the ladder
Adjuvants are included at every level of the analgesic ladder and may be the only analgesia needed for some conditions.

Some examples of adjuvants:

• Radiotherapy, bisphosphonates – pain from bone metastases
• Antimuscarinics (hyoscine) – bowel colic
• Antibiotics – cellulitis
• Glyceryl trinitrate spray – ischaemia
• Steroids – liver capsular pain

Step one: paracetamol and/or NSAIDs

Mild pain of many causes will respond to paracetamol. NSAIDs are also effective in treating mild to moderate pain, particularly if an inflammatory process is involved. If tolerated, it is recommended that these drugs are continued through the analgesic ladder.

Step two: add in a “weak” opioid

One advantage of weak opioids is that they do not require a controlled drug script. However they all act like morphine and have the same range of adverse effects. Consider that giving a patient 60 mg of codeine, four times per day, is the equivalent of 24mg of morphine in 24 hours (Table 1).

The general rules for weak opioid use are:⁶

• A weak opioid should be added to, not substituted for a non-opioid.
• There is no advantage of changing between weak opioids. Do not “kangaroo hop” from weak opioid to weak opioid.
• If a weak opioid is inadequate when given regularly, change to a strong opioid (e.g. morphine).

Step three: change to a “strong” opioid

Morphine is the most familiar strong opioid and therefore is first choice. To move a patient from a weak opioid to morphine, because their pain is not controlled, first work out what their current equivalent morphine dose is. For example 60 mg of codeine, four times per day, is the equivalent of 24mg of morphine in 24 hours (Table 1).

Therefore, because the pain was not controlled at this dose, a reasonable starting dose of morphine would be 20mg twice per day.

The dose of morphine is titrated until pain control is achieved or adverse effects are intolerable (Table 2). There is no top dose of morphine.

There are two ways of titrating:

Method 1:
Add up all the opioids taken in the previous 24 hours including regular and breakthrough doses. Divide this figure by two to make a new regular twice daily dose. Remember to recalculate a breakthrough dose, e.g. a patient on 30 mg twice per day who has taken four 10mg breakthrough doses, has a total 24 hour opioid dose of 100mg. The new regular dose would then be 50mg twice per day, with a breakthrough dose of 10–15mg — one sixth of the total 24 hour dose. Numbers can be rounded to make simple regimens with available strengths.

Method 2:
Increase the regular dose by 30 – 50%. For example, if a patient is on a total daily dose of 60mg, an increase of 30% would take this to 80mg and an increase of 50% would take this to 90mg. Choose whatever dose is easiest in terms of available strengths, e.g. 40mg, twice per day. Recalculate breakthrough dose.

Opioid rotation

Ongoing adverse effects may necessitate rotating to another strong opioid. Changing to another opioid requires calculating the equivalent morphine dose that the patient has been using (Table 3). Figures are approximate because individual patients metabolise opioids differently.

Patient apprehension about the use of morphine or the presence of impaired renal or liver function may necessitate selecting an opioid other than morphine.

Further reading: Chronic Pain: A Primary Care Condition. Available from www.arthritisresearchuk.org/