Chronic pain can prevent you from doing daily activities and also have an impact on your social and personal life. Therefore, the primary goal of treatment is to reduce the feeling of pain and help you get back to your activities, which are otherwise affected. Treatments for pain can be broadly categorized as pharmacologic and non-pharmacologic.
Pharmacologic Pain of Treatment
Pharmacologic treatment is the mainstay of pain therapy. The most important role of these drugs is to help facilitate functional restoration through analgesia (reduction of pain). The pharmacological drugs used for pain relief are classified as follows:
1. Non-opioid analgesics (non-opioids):
Acetaminophen (paracetamol), non-steroidal anti-inflammatory drugs (NSAIDs)
2. Opioid analgesics (opioids):
Morphine, codeine
3. Adjuvant analgesics or co-analgesics:
Antiepileptic drugs (AEDs), tricyclic antidepressants (TCAs), local anesthetics (LAs), etc.
Non-opioid Analgesics of Pharmacologic Pain
Aspirin and other related compounds constitute a class of drugs known as NSAIDs. The main therapeutic action of this class of drugs is the reduction of inflammation, fever, and pain. Acetaminophen is another important non-opioid analgesic, which causes a reduction of pain and fever, but lacks a specific anti-inflammatory effect.
How Do They Work?
These compounds are thought to act by inhibiting a chemical substance known as prostaglandin, which is responsible for causing inflammation in the body.
When Are They Indicated?
NSAIDs are indicated in a wide variety of musculoskeletal pain syndromes, including low back pain, osteoarthritis, ankylosing spondylitis, and rheumatoid arthritis. They are also beneficial in a number of other pain syndromes including dental pain, headache, etc.
What Are the Common Side Effects?
Gastrointestinal side effects (dyspepsia, ulcers, bleeding) are most commonly experienced with the use of NSAIDs. However, some drugs may also show platelet inhibition, liver dysfunction, and dizziness. In rare cases, NSAIDs can affect your heart and the rest of the circulatory system.
Table 1: Examples of Commonly Prescribed NSAIDs
Opioid Analgesics of Pharmacologic Pain
Opioid analgesics are commonly used in the management of various cancer pains as well as for non-cancer-related pains, such as neuropathic pain. Opioids are derived from or related to the Opium (poppy) plant.
How Do They Work?
Opioid analgesics relieve pain by acting directly on the central nervous system. They bind to the opioid receptors that are present in the nervous system and are involved in pain signaling and control. In simple words, these drugs modify sensory and affective aspects of pain.
When Are They Indicated?
Opioids are used to treat moderate to severe pain that does not respond to non-opioids alone. Opioids are mainly indicated in the treatment of acute pain (e.g., trauma, postoperative pain), breakthrough pain, cancer pain, and some types of chronic non-cancer pain (CNCP)
What Are the Common Side Effects?
The side effects of opioid analgesics include sedation, mental confusion, respiratory depression, nausea, vomiting, constipation, pruritus (itching), and urinary retention. Long-term use of opioids may also cause physical and psychological dependence (addiction).
Table 2: Examples of Opioid Analgesics
Note:
Subcutaneous, Intravenous, Intrathecal: Injectables
Adjuvant Analgesics of Pharmacologic Pain
Antidepressants
Tricyclic Antidepressants (TCAs) are useful in the treatment of some painful conditions such as headaches, cancer pain, and neuropathic pain. These drugs exert their effect by blocking certain chemical substances in the brain called serotonin and norepinephrine. The side effects of this class of drugs include sedation, dry mouth, blurred vision, and some cardiovascular effects (hypertension, arrhythmias).
Local Anesthetics (LA)
These drugs inhibit the generation of abnormal pain impulses created by nerves that are damaged. LAs are administered in several ways for different purposes. Topically applied LAs are used to treat neuropathic pain. Some LAs can be injected into tissue and around nerves to relieve pain in a particular region. Rarely, intravenous LAs (e.g., lidocaine) is used to manage neuropathic pain, arthritis, post-stroke pain, or headache.
Antiepileptic Drugs
The mechanism by which antiepileptic drugs exert analgesic effects is unclear. However, it could be through the suppression of abnormal discharges by the nerves that are damaged by an injury. Sedation, mental confusion, dizziness, nausea, or unsteadiness, are some of the side effects associated with this class of drugs.
Table 3: Examples of Antiepileptic Drugs, Antidepressants, and Local Anesthetics
Note:
Subcutaneous, intravenous, intrathecal, epidural: Injectables
Other Medications Pharmacologic Pain
Muscle Relaxants
Skeletal muscle relaxants are widely used in the treatment of pain. However, the mechanism by which they cause pain control is not very clear. Drugs such as metaxalone, methocarbamol, and orphenadrine are prescribed in relieving pain caused due to musculoskeletal conditions (low back pain). The side effects of these drugs include sedation, seizures, and cardiac effects.
Botulinum Toxins of Pharmacologic Pain
Botulinum toxins have been used in the treatment of pain disorders. Especially botulinum toxin type A may be helpful in managing chronic low back. It is also used in other painful diseases such as myofascial syndrome, headaches, arthritis, and neuropathic pain. When an appropriate amount of botulinum is injected into the muscle, it reduces muscle contraction. Common side effects include pain in the injected area, bruises, and muscular weakness. In some cases, fatigue and fever can appear one to two weeks after injection.
Tramadol Pharmacologic Pain
Tramadol is thought to exert its analgesic action partly through binding to the opioid receptor (opioid effect) and weakly by inhibiting some chemicals in the brain (non-opioid effect). It is indicated in the management of cancer-related pain and a wide variety of musculoskeletal pain syndromes. In higher doses, it may cause seizures. Other adverse effects include dizziness and nausea.
