pain Flashcards
define pain
unpleasant sensory/ emotional experience that can cause tissue injury
what are the types of pain
Acute- high intensity, conducted my small myelinated A-delta fibres. Lateral horn spinothalamic .
Chronic- over 6 months, chronic cancer is chronic and acute, non mg is conducted by UNmyelinated c-delta fibres medial smipiniothalamic tractand is low intensity for long duration e.g. radiculitis
Pathway of nociceptive pain (the jitty near the post)
transduction
transmission
perception
modulation
what occurs at transduction
-conversion of painful stimuli into a action potential 3 types of stimuli thermal, mechanical, chemical. Tissue releases PROSTAGLANDINS, subs P, Serotonin, bradykinin and histamine. Pain impulse travels to cns by neuromediators
describe what occurs at transmission
Stimuli is converted into an action potential by influx of na and k ions and processed in the brain
Ascending tracts: neo-spinothalamic( contralateral) paleo and archi spinothalamic (bilat)
what drugs cause modulation of the pain pathway at transmission
Local anesthetics and anticonvulsants decrease the ion exchange and decrease transmission
Opioids block neurotransmitter release: glutamate, ach, norepinephrine, serotonin, subs p
what drugs cause modulation of the pain pathway at transduction
NSAIDS inhibit COX ->decrease pg ->decrease pain sensation. Corticosteroids inhibit arachidonic acid-> decreased pg, useful in cancer and radiculitis.
describe what occurs at pain perception
ccurs in the cortex. Thalamus, sensorimotor cortex, insular cortex,anterior cingulate register the AP as specific pain points in the body
-amygdala and hypothalamus detect intensity
what tract does modulation occur
descending tract by serotonin, norepinephrin and enkaphalin at the substantia gelatinosa
types of nociceptive pain:
Somatic: well localised. Skin bones fascia meninges peritoneum, pleura and teeth
Visceral: poor loc, even distant. Heart, gut and bladder (ORGANS)
paracetamol moa
inhibits cox 3 in brain. Analgesic and antipyretic
paracetamol pk
oral abs. Rapid absorp. Tmax is 3 hrs w/ suppositories. Liver metabolism
paracetamol indication
mild/mod pain. Headache, muscle etc pregnant women and babies over 3 months
paracetamol ADR
no side effects in ti. Hepatotoxicity and renal toxicity at overdose. Liver failure due to excess N ACETYL-P-BENZOQUINONE-IMINE (NAPQI)
paracetamol dose
dults- 4g max. 1g Every 6 hrs. Kids. 60mg/kg/24hrs.
paracetamol antidote
N-ACETYLCYSTEINE (NAC)
paracetamol CI
liver or renal failure.
Metamizole MOA
prodrug w/ active metabolites. Analgesic, antipyretic, spasmolytic. Slightly antiinflamm
Metamizole pk
oral abs
Metamizole inidication
mild/mod- head and toothache, myalgia, neuralgia, chole and nephrolithiasis.
Metamizole CI
Ci: avoided in pregs and breastfeeding. Reduced in renal and liver failure. Incresed dose in smokers due to faster metabolism.
Metamizole dose
max is 3g. 15yrs n over 1g x3
Metamizole ADR
interstitial nephritis, agranulocytosis, allergic reaction in intravenous admin.
classification of NSAIDS
Salicylic acid derivatives- aspirin- tab 100mg
Acetic acid derivatives- indomethacin
Oxicam derivatives - meloxicam(selective cox 2) piroxicam
Phenylacetic acid derivatives - diclofenac, aceclofenac
Coxibs- celecoxib- 200mg
Others- nimesulide
Propionic acid derivatives
Ibuprofen- tab 200 mg
Ketoprofen- tab 50mg
Naproxen- tab 250 mg
NSAID moa
inhibit cyclooxygenase 1 and 2 to prevent production of pg thromboxane, prostacyclin. Selective nsaids act on cox 2 only. Aka coxib (celecoxib)
Organ effects of PGE2. Gastric mucosa: decrease hcl, increase mucosal protection. Kidney: renal artery dilation to increase blood flow. Platelets: inhibit agg. Mediates pain
Cox2 is inflammatory mediator, increases inflamm. Activity of nsaids against cox2 increases with time
NSAID indications:
chronic inflammatory diseases- arthritis, spondylitis, radiculitis, metastatic bone tumors due to prostaglandin release during bone lysis
NSAID ADR
ulcers, nausea and vom. Less common with coxibs.
Nephrotoxicity due to sodium and water retention caused by reduced blood flow from prostaglandin inhibition.
Interstitial nephritis.
Prolonged bleeding due to decreased thromboxane with is supposed to aggregate platelets
Hypersensitivity- asthma- due to increase in leukotrienes due to pg decrease. Leukotrienes cause bronchoconstriction and increased secretion of goblet cells. Coxibs are cox 2 specific so don’t cause asthma