What Does Analgesic Do to the Body?
Analgesics or pain killers are drugs used to relieve pain without losing consciousness. They are classified into the following categories:
- Nonopioid Analgesics
- Opioid Analgesics
- Adjuvant Analgesics
Nonopioid Analgesics include drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and dipyrone.
Opioid Analgesics or narcotic analgesics include drugs such as morphine, codeine, tramadol, and tapentadol.
Adjuvant Analgesics include drugs such as GABA agonists, neuroleptics, muscle relaxants, and anticholinergics.
Depending on the mechanism of action and usage, analgesics can be further divided into the following subcategories:
- Nonsteroidal Anti-Inflammatory Drugs
- Cox-2 Inhibitors
- Opioid Analgesics
- CGRP Inhibitors
- Miscellaneous Analgesics
- Adjuvant Analgesics
1. What Is the Mechanism of Action of Analgesics?
1.1. What Are Nonsteroidal Anti-Inflammatory Drugs?
NSAIDs are a group of drugs used to relieve pain, reduce inflammation, and fever by targeting the two cyclooxygenases (COX) enzymes, COX-1, and COX-2, responsible for the production of prostaglandins from the fatty acid arachidonic acid in the body [1].
Prostaglandins are lipid compounds that have hormone-like effects and are found in all tissues of our human body.
They are synthesized (produced) by the walls of the blood vessels and involved in the regulation of smooth muscle contraction and relaxation, including those of the blood vessels, uterus, gastrointestinal tract, and urinary bladder.
For example, prostaglandins are responsible for the vasoconstriction and vasodilatation of blood vessels.
They are also involved in inflammation through their role as proinflammatory mediators during the acute phase of inflammation.
Additionally, prostaglandins induce fever through their action on the thermoregulatory center in the hypothalamus.
Another function is associated with their role in platelets aggregation during coagulation, and therefore, are also involved in thrombosis (formation of blood clots in the blood vessels).
Thus, NSAIDs by inhibiting the enzymes COX-1 and COX-2, prevent the production of prostaglandins resulting in pain relief, reduction of inflammation, and fever, and prevention of thrombosis.
The most known NSAIDs are aspirin (acetylsalicylic acid), ibuprofen (Advil, Nurofen, Motrin), and naproxen (Aleve, Naprosyn).
- What Are NSAIDs Used to Treat?
NSAIDs are used for the relief of mild-to-moderate pain in conditions and disorders such as headaches, migraines, toothache, menstruation, muscle strains and sprains, rheumatoid arthritis, and osteoarthritis.
1.2. What Are Cox-2 Inhibitors?
COX-2 inhibitors are also NSAIDs used to relieve pain, reduce inflammation, and fever; however, these drugs selectively target COX-2, while the other NSAIDs target both COX-1 and COX-2.
The advantage of the COX-2 inhibitors is their reduced side effects on the gastrointestinal tract when compared with the other NSAIDs. However, some concerns were raised about the safety of some COX-2 drugs.
COX-2 inhibitors include drugs such as celecoxib (Celebrex) and rofecoxib (Vioxx), which were withdrawn from the market.
- What Are COX-2 Inhibitors Used to Treat?
Cox-2 inhibitors are used for the relief of mild-to-moderate pain in conditions and disorders such menstruation, hereditary polyps of the colon, ankylosing spondylitis, rheumatoid arthritis, and osteoarthritis.
1.3. What Are Opioid Analgesics?
Opioid analgesics or narcotic analgesics are used for the relief of moderate-to-severe acute or chronic pain.
This class of analgesics includes drugs such as morphine, codeine, tramadol, and tapentadol.
These drugs relieve pain through their binding to the opioid receptors (e.g., mu receptors) found in the brain, spinal cord, peripheral nerves, and gastrointestinal tract [2].
The increased prescriptions of opioid analgesics resulted in less effective therapy, and substance abuse [3].
- What Are Opioid Analgesics Used to Treat?
Opioid analgesics are used for the relief of mild-to-moderate pain associated with cancer, and for palliative care or end-of-life care. However, due to their oversubscription, they have been used for the relief of all types of pain.
1.4. What Are CGRP Inhibitors?
CGRP Inhibitors are drugs that relieve pain by targeting a peptide in the peptide known as Calcitonin gene-related peptide (CGRP) [4].
CGRP is stored in neurons of the brain, spinal cord, and peripheral nervous system, where it is involved in the transmission of pain.
CGRP Inhibitors include monoclonal antibodies that bind specifically to CGRP and block its action, including eptinezumab (Vyepti), galcanezumab (Emgality), and fremanezumab (Ajovy) and monoclonal antibodies that bind to the CGRP receptor such as erenumab (Aimovig).
- What Are CGRP Inhibitors Used to Treat?
CGRP Inhibitors are used to treat patients with frequent, episodic, or chronic migraine headaches.
1.5. What Are Miscellaneous Analgesics?
Miscellaneous Analgesics are a separate class of analgesics as they belong to neither nonsteroidal anti-inflammatory drugs (NSAIDs) nor opioid analgesics.
They include analgesics such as acetaminophen (Paracetamol, Tylenol), ziconotide, and dipyrone. However, in the United States, only acetaminophen and ziconotide are available.
- What Are Miscellaneous Analgesics Used to Treat?
Acetaminophen (Paracetamol, Tylenol) is used for reducing fever and relieving mild-to-moderate pain associated with conditions and disorders such as headaches, migraines, toothache, muscle strains, and sprains, rheumatoid arthritis, and osteoarthritis.
Ziconotide relieves severe pain by blocking N-type voltage-gated calcium channels found in the dendrites and nerve terminals and is involved in neurotransmission and pain transmission.
Dipyrone (Metamizole) is used as a pain killer, spasm reliever, and anti-inflammatory agent for the relief of acute and chronic forms of pain, high fever, acute injury, colic, and cancer pain; however, metamizole is banned in many countries including the United States.
1.6. Adjuvant Analgesics
Adjuvant analgesics are drugs that are not considered analgesics but are used for neuropathic pain, musculoskeletal pain, or cancer pain.
This group of drugs includes antidepressants, α2-adrenergic agonists, corticosteroids, neuroleptics, muscle relaxants, and anticholinergics [2].
2. Do Analgesics Reduce Inflammation?
Analgesic drugs such as NSAIDs and COX-2 inhibitors are used to relieve pain and reduce fever, and inflammation.
The mechanism of action involves the inhibition of the production of the proinflammatory peptide prostaglandins.
3. Is Analgesic Good for Fever?
Analgesic drugs such as NSAIDs and COX-2 inhibitors are used to relieve pain and reduce inflammation, and fever.
The mechanism of action involves the inhibition of the production of prostaglandins which induce fever through their action on the thermoregulatory center in the hypothalamus.
4. Is Ibuprofen an Analgesic?
Ibuprofen (Advil, Nurofen, Motrin) is a nonsteroidal anti-inflammatory drug used to relieve pain, reduce inflammation, and fever by targeting COX-1, and COX-2 enzymes, responsible for the production of prostaglandins.
Conclusion
Analgesics are used for pain relief, and for the reduction of inflammation and fever. They are differently used depending on the severity of the pain; however, their oversubscription or misuse can result in disorders affecting the gastrointestinal tract (e.g., NSAIDs) or drug abuse (e.g., opioid analgesics).
