Classification of Pain Medications (Analgesics): Nociceptive & Neuropathic Analgesics

Pain medications are also known as analgesics. Pain medications are used to treat the nociceptive and neuropathic pain.

Nociceptive Pain

Nociceptive pain is initiated by irritation or injuries of peripheral pain receptors and sensory nerve fibers. Sensory nerve fiber carries pain impulses or signals to spinal cord and brain. Peripheral pain receptors are spread over skin, subcutaneous tissue, muscles, bones, joints, ligaments and tendons. The pain receptors in spinal cord and brain are known as central pain receptors. Irritation of pain receptor is caused by injuries and stimulations by chemicals that is secreted during tissue inflammation.

Tissue inflammation is a physiological defense mechanism to fight and prevent further tissue injury. The tissue inflammation follows injury, infection and surgical incision. The chemicals secreted by inflamed tissue are bradykinin, serotonin and prostaglandin. Prostaglandin and several other chemicals which are secreted by inflamed tissue irritates the pain receptors resulting in acute pain. Acute pain lasts for less than 6 months and pain is considered chronic if pain continues for 6 months and longer. Skin diseases like boil, impetigo, carbuncle, furuncle, boil, cellulitis and abscess causes moderate to severe inflammation of skin and subcutaneous tissue. Tissue inflammation increases secretion of prostaglandin and bradykinin that irritates pain receptors and sensory nerve fibers results in moderate to severe nociceptive pain. Similarly, muscle tear, laceration and spasm also causes mild to severe muscle inflammation and increases secretion of prostaglandin that results in acute pain. The intensity of pain depends on severity of inflammation. Abundant amount of prostaglandin is secreted when inflammation and infection is widely spread within soft tissue. The cause of nociceptive pain if inadequately treated then long standing nociceptive pain become neuropathic pain.

Nociceptive pain is treated with NSAIDs for 2 to 3 weeks. Most nociceptive pain caused by trauma, infection and surgery last for 2 to 3 weeks. Nociceptive pain lasting 1 to 6 months may need adjuvant medications or alternative treatment. The alternative treatment is opioids for 1 to 3 weeks and should be discontinued once wound is healed and the pain subsides. Other treatments includes physical therapy and massage therapy.

Neuropathic Pain

Neuropathic pain is caused by abnormal physiological changes of peripheral and central (spinal cord) pain receptors as well as sensory nerve fibers. Such changes follow prolonged, severe, continuous or intermittent pain. The causes of neuropathic pain are neuropathy (diseases of central and peripheral receptors, sensory nerve fibers and spinal cord), spinal cord tumor and diseases of brain that affects pain centers. The most common cause of neuropathic pain is diabetic neuropathy that affects peripheral pain receptors and sensory nerve fibers. The interneuron are the cells that lies within spinal cord. Interneuron connects and transmits signal from peripheral tissue to brain. Damaged or abnormal interneuron often interprets and transmits signals like touch, temperature or pressure as a pain. Such impulses are then transmitted from spinal cord to brain as a pain impulse. These signals known as neuropathic pain are interpreted as severe intense electric shock like burning pain. The neuropathic impulses are generated within peripheral receptors or central receptors and carried to spinal cord and brain. Severe continuous neuropathic pain causes anxiety, depression, functional impairment and sleep deprivation. Most of the neuropathic pain do not respond to NSAIDs or opioids.

Neuropathic pain responds to selective antidepressants and antiepileptic medications. These analgesic are known as neuropathic analgesics or pain medication. Neuropathic pain resulting in anxiety disorder and depression need to be treated with neuropathic pain medications and alternative treatment. Alternative treatment may include massage therapy, physical therapy, mineral pill and homeopathic medications.

Classification of Pain Medications (Analgesics)

Classification of Pain Medications (Analgesics): Nociceptive & Neuropathic Analgesics-

  1. Nociceptive Analgesics

    1. NSAID (Non-Steroidal Anti-Inflammatory Drugs)

      1. COX 1 inhibitors- Blocks cyclooxygenase type 1 enzyme.

        • Aspirin
        • Ibuprofen also known as Motrin and Advil
        • Naproxen also known as Aleve, Anaprox, Naprelan and Naprosyn.
        • Indomethasine also known as Indocin
        • Oxaprozine also known as Daypro
        • Ketoprofen
        • Ketorolac also known as Toradol
        • Salsalate also knownas Disalsate and Amigesic
        • Diclofenac also known as Cambia, Cataflam, Voltaren, Zipsor and Zorvolex
        • Diflunisal also known as Dolobid
        • Piroxicam also known as Faldene
        • Etodolac also known as Lodine
        • Nobumetone also known as Relafen
        • Sulindac also kown as Clinoril
        • Tolmetin also known as Tolectin
      2. COX 2 inhibitors- Blocks cyclooxygenase type 2 enzyme.

        • Celebrex
        • Rofecoxib also known as Vioxx
        • Valdecoxib also known as Bextra
    2. Opioids

      1. Short Acting Opioids
      2. Long Acting Opioids
        • Morphine controlled release
        • MS Contin
        • SR Morphine
        • Kadian (Morphine extended‐ release capsule)
        • Avinza
        • Oxycontin (Oxycodone controlled‐ release)
        • Opana ER (Oxymorphone extended‐release)
        • Exalgo ER (Hydromorphone extended‐release)
        • Duragesic patch (control release Fentanyl transdermal)
        • Buprenorphine transdermal
        • Methadone
  2. Neuropathic Analgesics

    1. Anti-depressant analgesics

      • Amytriptyline (Elavil)
      • Dosulepin also known as dothiepin (Tricyclic antidepressants)
      • Nortriptyline also known as Allegron, Aventyl, Noritren, Nortrilen, and Pamelor (Tricyclic antidepressants)
      • Fluoxetine, also known by trade names Prozac and Sarafem (Selective Serotonin reuptake inhibitor)
      • Duloxetine (Cymbalta)
      • Venlafaxine (Effexor)
      • Desvenlafaxine (Pristiq)
      • Minacipran (Savella)
    2. Anti-epileptic Analgesics

      • Phenytoin (Dilantin)
      • Sodium Valproate (Convulex and valproic acid)
      • Carbamazepine (Tegretol, Carbatrol, Epitol and Equetro)
      • Gabapentin (Neurontin, Gralise, Horizant, Gralise and Neuraptine)
      • Pregabalin (Lyrica)
      • Mexilentine (Mexitil)

References-

  1. Peripheral and spinal mechanisms of nociception in a rat reserpine-induced pain model.

    Taguchi T1, Katanosaka K, Yasui M, Hayashi K, Yamashita M, Wakatsuki K, Kiyama H, Yamanaka A, Mizumura K Pain. 2015 Mar;156(3):415-27. doi: 10.1097/01.j.pain.0000460334.49525.5e.

  2. Neuropathic pain

    Luana Colloca,1 Taylor Ludman,1 Didier Bouhassira,2 Ralf Baron,3 Anthony H. Dickenson,4 David Yarnitsky,5Roy Freeman,6 Andrea Truini,7 Nadine Attal,8 Nanna B. Finnerup,9 Christopher Eccleston,10,11 Eija Kalso,12David L. Bennett,13 Robert H. Dworkin,14 and Srinivasa N. Raja15

    Nat Rev Dis Primers. 2017 Feb 16; 3: 17002.

  3. Analeptic drugs to treat neuropathic pain or fibromyalgia- an overview of Cochrane reviews.

    First published: November 11, 2013.

  4. Treatment of chronic pain: antidepressant, antiepileptic and antiarrhythmic drugs

    Sally-Ann Ryder, MRCP FRCA, Catherine F Stannard FRCA

    Continuing Education in Anaesthesia Critical Care & Pain, Volume 5, Issue 1, 1 February 2005, Pages 18–21

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