Pain is a common problem, and it is essential that doctors know how to treat it. It is recognised that many psychosocial factors affect people’s perception of pain, in particular of chronic pain. This revision article describes the pain ladder and the pharmacology and uses of the analgesia it recommends.
The WHO Pain Ladder
- The World Health Organisation pain ladder is a way of determining the strength of analgesia a patient requires.
- Determining the level of pain a patient is in can be done in several ways: asking them to rate this on a scale of 1-10; asking them what the pain prevents them from doing (e.g. sleeping); examining for altered physical signs such as increased respiratory and heart rates.
- It is best to prescribe medications, every few hours rather than PRN (particularly in hospital) as otherwise the patient is likely to be in pain between the doses1.
NSAIDs
- Non-steroidal anti-inflammatory drugs provide effective analgesia for mild- moderate pain, and are particularly good for musculoskeletal injuries as they reduce the pain and additionally lower the inflammation.
- They are also antipyretics.
- Examples include ibuprofen, paracetamol and diclofenac.
- Prostaglandins are cell signalling molecules that are involved in the inflammatory and pain response. They are synthesised from arachidonic acid by the enzymes COX-1 and COX-2.
- The action of NSAIDs is to inhibit the COX enzymes, reducing the inflammatory response and therefore the sensation of pain.
- The main side-effects caused by the medications are because the prostaglandins produced by COX-1 have other important functions besides the inflammatory cascade: they are also involved in the regulation of the renal parenchyma, the gastric mucosa and the myocardium. This can cause gastric ulcers, and reduced renal perfusion in those who already have cardiac, renal and liver problems.
- This is why COX-2 specific analgesics are sometimes used (celecoxib), but they have been associated with cardiac problems.
- Other side effects include hypersensitivity reactions and increased bruising and bleeding.
- Paracetamol is slightly different to the other NSAIDs: it can be used safely in combination with other NSAIDs and has no anti-inflammatory properties. Its mechanism of action is not completely understood: it is known to act weakly on the COX enzymes, but this does not explain its full effects.
- NSAIDs are very effective when combined with opiates, so don’t rush to giving a patient in pain morphine straight away, move on to step 2 first.
- Example prescribing schedule:
- Paracetamol: 1g QDS PO
- Diclofenac: 50mg TDS PO
- Ibuprofen: 400mg QDS PO
Opioids
- Opioid drugs are very good for visceral pain. These drugs are often used in the emergency department for acute severe pain, for childbirth, peri-operative pain control and for cancer pain.
- Mild opiates may be given on their own, e.g. codeine, or in combination with a non-opioid e.g. co-codamol (codeine combined with paracetamol).
- Examples of strong opiates include morphine and fentanyl.
- Opioids act on 3 receptor types in the CNS: μ (mew), κ ( kappa) and δ (delta). The μ receptors are then subdivided into type 1 and type 2.
- Type 1 reduces the sensation of pain by inhibiting the transmission of pain signals ascending the nerves of the spinal cord, whilst interaction with type 2 receptors produces the unpleasant side effects of opioid drugs such as constipation, drowsiness, nausea and vomiting, and most seriously respiratory depression.
- An excess of an opioid drug can be managed by administering the drugs naloxone or naltrexone.
- Example prescribing schedule:
- Co-codamol; 8/500, 2 tabs QDS PO
- Codeine; 60mg QDS PO
- Morphine; 10mg QDS SC/IM
Alternative methods of analgesia
- If none of the above has worked, or the pain is too chronic for the patient to continue taking strong opioids, then there are alternative analgesics.
- Diazepam and other benzodiazepines can be used for muscle spasm.
- Tricyclic antidepressants such as amitriptyline can be used to manage neuropathic pain.
- Anticonvulsants may also be used for neuropathic pain, for example carbamazepine.
- Finally, a pain management programme or physical methods of pain management such as nerve blocks, joint injections, and acupuncture may be useful.
- Example dosing regimen:
- Amitriptyline; 75mg NOCTE PO
- Diazepam; 3mg TDS PO
Conclusion
Different types of pain respond to different analgesics. For mild pain, paracetamol is a safe starting point. For pain of musculoskeletal origin such as arthritis, NSAIDs are very effective. Mild opioids such as codeine are beneficial for more severe pain, whilst strong opioids such as morphine, fentanyl and pethidine should be reserved for operations, labour and cancer pain. Alternative pain management techniques such as local anaesthetic injections, tricyclics and pain management programmes may be more suitable for pain of neuropathic origin or of a longer duration.
