Simply put, pain is an unpleasant sensation derived from actual or perceived injury (there is an emotional component to it). It is usually initiated by a harmful (tissue-damaging, noxious) stimulus. As a matter of fact, identifying and resolving the underlying cause of pain is vital.
Pain is the most common symptom and is important because it both signals disease and aids diagnosis. It is necessary pharmacists take any complaints of pain seriously. The management of pain is a primary clinical imperative.
Pain can be quantitatively assessed by degree of severity using verbal and visual rating scale. Though subjective, it can be evaluated using clinical, laboratory and imaging techniques to aid diagnosis.
Several chemical mediators including peptides, neurotransmitters and inflammatory agents are implicated in the induction of pain. Interfering with these substances, directly or indirectly, is the basis for analgesia. For example, aspirin inhibits prostaglandin biosynthesis, morphine mimics endorphin peptide by acting on μ-receptors, and tricyclic drugs (antidepressants) block neuronal amine uptake.
Analgesics come in different dosage forms ranging from oral and parenteral to topical. Analgesics from different classes (with different mechanisms of action) are usually combined to improve efficacy, and spare higher doses of the individual drugs. For example, a fixed dose combination of paracetamol and codeine…
- Pain is usually treated in a step-wise manner according to severity. A perfect instance is in cancer pain treatment. The WHO analgesic ladder is referred to.
- Local anaesthetics provide analgesia too but do not fall within the scope of this article.
- Acute pain can be managed effectively using analgesic drugs, and is often self-limiting. Persistent pain may be considered as pain which continues beyond the usual time required for tissue healing.
- Treatment may involve a multidisciplinary approach and includes both pharmacotherapy and psychotherapy (non-pharmacological)
Pharmacotherapy of pain
- Useful in mild to moderate pain.
- Paracetamol is an anti-pyretic and mild analgesic with few, if any, anti-inflammatory properties
- It has no irritant effect on the gastric mucosa and can be used safely and effectively in most individuals who are intolerant of NSAIDs.
- There is the risk of liver damage when ingested in doses higher than 4 g in a day, with alcohol, or by people with already existing liver problems.
- Patients should be aware that over-the-counter cough and cold medicines often do contain paracetamol, so as to avoid mistakenly ingesting extra doses of paracetamol from other sources.
Non-steroidal Anti-inflammatory Drugs (Aspirin, Ibuprofen, Celecoxib)
- Has both analgesic and anti-inflammatory properties.
- Causes significant relief from pain due to inflammation as observed in arthritis, bone fracture, tumours, muscle pains, headache and acute pain caused by injury or surgery.
- Non-selective NSAIDs like Diclofenac can cause gastrointestinal ulcers, while selective NSAIDs (COX-2 inhibitors) have fewer gastrointestinal adverse effects. Furthermore, caution should be exercised in renal insufficiency, asthma, hypertension and cardiac related events.
Opioids (morphine, methadone, oxycodone, etc.)
- Opioids are indispensable to the management of acute and chronic pain. They relieve moderate to severe acute pain. A typical example is cancer pain
- The efficacy and safety of long-term use of opioids to treat chronic pain has been questioned as instances of addiction and death from their misuse have mounted.
- Opioids are no longer first-line treatment of chronic pain, and a more conservative approach may involve other drug classes, such as NSAIDs, anticonvulsants, and antidepressants.
- Side effects, some of which are life-threatening, include constipation, sedation, nausea and vomiting, respiratory depression, addiction, narrowing of airways and pruritus.
Adjuvant analgesics (prescription-only)
- Anticonvulsants: commonly used to treat different pain syndromes like post-herpetic neuralgia, peripheral neuropathy and migraine_basically pain due to nerve dysfunction. E.g. gabapentin.
- Antidepressants: commonly used in chronic pain conditions like musculoskeletal pain, fibromyalgia and neuropathic pain. E.g. amitriptyline, duloxetine
- Skeletal muscle relaxants: used to relieve pain triggered by muscle spasm. Eg Tizanidine, baclofen.