Pharmacological Management of Pain

By Dr.Rochana Perera

 

Introduction

     Pain management strategies could be broadly divided into two categories, pharmacological and non-pharmacological. Non-pharmacological methods will be discussed in a separate chapter. There are a few facts one needs to remember in managing pain.

Pain is a very subjective sensation. What is unbearable to one person may be just a minor inconvenience to another (for example, labor pains in primi para and multi para).

Nature has provided us with our own analgesic system so one might not feel pain despite serious injury (for example, war and sports injuries).

Acute pain is severe, short lasting and responds relatively well to drug therapy. Chronic pain on the other hand is of relatively low intensity, of longer duration and responds poorly to conventional analgesics.

 

Analgesic drugs

     There are many analgesics. They act by blocking the pain pathways at certain points. For our convenience, we divide them into 3 groups, namely simple analgesics, intermediate analgesics and potent (strong) analgesics. Paracetamol and NSAIDs belong to simple analgesics.  Tramadol and codein are considered as of intermediate potency. Opioid drugs such as morphine, pethidine and fentanyl are strong analgesics.     

     However, the most potent analgesic effect is produced by the drugs of the local anesthetic group. As these are administered by complicated techniques and are restricted to certain group of patients under specialized care units, details of the local anesthetic drugs will not be discussed in this section. As a general rule, mild pain must be treated with simple analgesics. Moderate pain is treated with (simple and) intermediate analgesics. Severe pain must be treated with strong analgesics with or without simple and intermediate drugs.

 

Adjuvant drugs

     These are a group of non-analgesic drugs, which help to relieve pain only in certain painful conditions (Table 1). For example, carbamazepine relieves pain of trigeminal neuralgia, but has no effect in migraine or post-operative pain. These drugs usually do not block the pain pathways, but modify the signals of descending pathways and the activity of higher centers or act by some unknown mechanism.

 

Analgesic ladder

     The WHO has proposed an analgesic ladder, a guide mainly for use in managing chronic pain. But, it could be used in managing acute pain as well. If you are not sure of the intensity of the pain, you start with a simple drug and gradually escalate the treatment until satisfactory analgesia is achieved. Please note the usefulness of adjuvant drugs at every stage, as they are very useful in chronic pain management.

 

Table 1. Examples of Adjuvant Analgesics

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5.  Analgesic ladder

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Commonly used analgesic drugs

Paracetamol

     This is the most commonly used analgesic drug. It is very effective for mild pains such as headaches, myalgia etc. It has an antipyretic property as well. It is available as tablets, syrup and as suppositories but there are no IV preparations. At recommended doses the side effects of paracetamol are minimal.

 

NSAID (Non-Steroidal Anti-Inflammatory Drugs)

     Drugs such as aspirin, diclofenac, and ibuprofen belong to this group. NSAIDs have anti-inflammatory properties as well, and therefore are more potent than paracetamol. NSAIDs act by inhibiting prostaglandin formation, both centrally and peripherally. Serious side effects include coagulopathy, gastric erosions, renal failure and broncho-constriction.

 

Tramodol 

     This is an intermediately potent drug. It acts on both opioid receptors, as well as serotonin receptors of the spinal cord. It is available as IV and oral preparations, and as suppositories. Nausea, vomiting and constipation are common side effects. It does not cause respiratory depression.

 

Opioids

     Morphine and pethidine belong to this group. They are very strong analgesics, and are very useful in acute conditions such as trauma and post-operative pain. Opioids are also used in terminal cancer pain. Common side effects include nausea, vomiting, sedation and constipation. There is a reluctance to use these drugs in wards because of the fear of respiratory depression and dependence. These are very rare possibilities at the recommended dosages. Therefore the patients should not be deprived of these excellent analgesics.

 

References

Justin DM. Pain 2005- An updated Review: Refresher course syllabus. IASP press. Seattle: 2005.

Warfield CA, Fausett HJ. eds., Manual of Pain Management, 2nd Edition. Lippincott Williams and Wilkins; Philadelphia: 2002.

Beaulieu P, Lussier D, Poreca F, Dickenson AH. (eds.), Pharmacology of Pain, IASP Press, Seattle, 2010.