Introduction to Analgesics

Question 1

International Association for Study of Pain (IASP) definition of pain

Answer 1

Pain is unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage; pain is perceived

Question 3

Physiology of Pain Perception

Pain Pathway

Answer 3

Via spinothalamic tracts (anterior or lateral)and spinobulbar tracts
1. stimulation of nociceptors
2. Transmission via 1st order neuron fibers (A-beta for non-noxious mechanical, A-delta for noxious mechanical, C for noxious heat and chemical)
3. Modulation of pain at dorsal horn from Periaqueductal Gray (Opiooids, GABA, Bradykinin, Histamine, Serotonin, Capsaicin)
4. 2nd order neuron from dorsal horn to thalamus
5. 3rd order from thalamus to certain part of homunculus of somatosensory cortex for perception/interpretation of pain
6. Spinobulbar tract projects to amygdala and hypothalamus to convey affective/intensity aspects of pain, able to recruit descending controls
7. Descending pain control pathways via Periaqueductal Grey can promote/inhibit passage of nociceptive information from dorsal horn

Question 4

Gate Control Theory: Endogenous Regulation of Pain

Pain and endogenous analgesia

Answer 4

Nociceptors may be inhibited via Enkephalins (endogenous opioids) by mechanoreceptors or may also be inhibited by fibers in limbic system

Question 5

Types of chronic pain

Answer 5

1. Nociceptive (i.e. OA, RA)
2. Neuropathic may be central (i.e. post stroke, MS, SCI, phantom limb) or peripheral (i.e. diabetic neuropathy, HIV related, post herpetic neuralgia)
3. Mixed (i.e. LBP, cancer, fibryomyalgia)
4. Visceral (i.e. internal organs, pancreatitis, IBS)

Question 6

Acute vs Chronic Pain

Answer 6

Acute: generally unknown/known cause, short and well characterized duration of pain, tx includes resolution of underlying cause
Chronic: unknown cause, duration persists after healing >3mo, tx includes pain control not cure

Question 7

Nociceptive Pain

Answer 7

caused by activity in neural pathways in response to potentially tissue-damaging stimuli (i.e. post operative pain, mechanical LBP, sports/exercise injuries, CRPS, sickle cell crisis, arthritis)

Chronic pain

Question 8

Mixed Type of Pain

Answer 8

Caused by combination of both primary injury and secondary effects

Chronic pain

Question 9

Neuropathic Pain

Answer 9

Initiated or caused by primary lesion or dysfunction in nervous system

Central or peripheral

Question 10

Domains of Chronic Pain

Answer 10

QOL, Psychological Morbidity, Social Consequence, Socioeconomic consequences

Question 11

Allodynia

Answer 11

pain from stimulus that does not normally evoke pain (thermal, mechanical)

Question 12

Hyperalgesia

Answer 12

Exaggerated response to painful stimulus

Question 13

Hyperesthesias

Answer 13

Exxagerated response to touch

Question 14

Hyperpathy

Answer 14

persistent pain even after cause of pain has been removed

Question 15

Analgesics

Answer 15

aka painkiller, any member of group of drugs used to achieve analgesia or relief fro pain
* two categories: Opioids and nonopioids

Question 16

Nonopioids

Answer 16

composed of drugs such as acetaminophen, aspirin, ibuprofen, etc.

Question 17

Opioids

Answer 17

Group of naturally occurring semisynthetic and synthetic agents that are characterized by their ability to relieve moderate-severe pain

Question 18

Analgesics by site of action

Answer 18

1. Brain (perception and modulation)- opioids, NSAIDS, Ketamine, TCAs, GABApentinoids, Benzodiazepines
2. Spinal Cord (transmission and descending modulation)- Opioids, Neuraxial local anesthetics epidural, ketamine, alpha-agonist, TCA
3. Peripheral nerve (transmission)- Nerve block with local anesthetic, ketamine, alpha-agonist, TCAs, opioids
4. Tissue (transduction)- local anesthetic infiltration, opioids, NSAIDS, corticosteroids, cooling, immobilization, elevation