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What is pain made up from?
Stimulus and emotional perception
What are the two types of the occurrence of pain and how are they managed?
- Acute - treat the cause may be possible rather than symptom
- Chronic - preferable to treat in anticipation
What are the four types of sensory fibres and what do they sense?
A aplha - proprioception, low threshold of activation
A beta - low intensity touch, vibration, pressure, low threshold for activation
A zeta - sharp pain, high threshold for activation
C fibres - transmit throbbing pain, slower conduction, non myelinated
Nociciptive fibres can be activated without specific receptor - direct activation. Some receptors detect stimuli, give examples:
- Heat > 42, acid pH, capsaicin, very hot, mustard (TRPV1)
- Cold, methanol (TRPV8)
- Mechanical stimuli (TRPA)
- ATP from damaged cells (P2X and P2Y ATP receptors)
- low extra cellular pH (lactic acid) (ASIC)
Name NSAIDS? What is a COX-2 inhibitor?
- Celecoxib - COX-2 inhibitor
What are the functions of COX-1 and COX-2?
- COX-1: 'housekeeping'
- constitutive expression
- gastric protection, vascular homeostasis, platelet aggregation, kidney function.
- COX-2: 'inducible'
- constitutive expression in the brain, kidney (see coxib ADR) bone
- Induced during inflammation (expression inhibited by glucocorticoids)
What are the functions of prostaglandins?
- They bind GPCR to act as local signalling molecules
- PGE2 increases sensitivity of nociceptive fibres
- Pyrogne - increase PGE2 synth (leukcyte) raises temp set point (hypothalamus)
- Role within inflammatory process
- GI protection (COX-1)
- PGI2 (prostacyclin) inhibits gastric acid secretion
- PGE2, PGF2 stimulate protective mucous secretion
- Platelet aggregation
- Prevents activation
- PGE2 and PGI2 maintain renal perfusion - synthesised in response to reduced perfusion
- Inhibit prostacyclin induced vasodilation
How does aspirin work?
Irreversible acetylation of COX1 and 2
What is the two chemical derivative of NSAIDs?
Propionic acid and Acetic acid
What drugs are propionic acid derivatives, how do they work? What are the indications? Cautions? Contraindications? Drug interactions?
- Inbuprofen, naproxen, ketoprofen.
- Reversible COX1 and 2 inhibitors
Anti-pyretic, anti-inflammatory, analgesic: arthritis, back pain.
Renal insufficiency, hypertension, avoid pregnancy.
Active peptic ulcers, sever heart failure
Avoid concomitant use with anticoagulation
What drugs are acetic acid derivatives, how do they work? What are the indications? ADR? Cautions? Contraindications? Drug interactions?
Reversibly inhibit COX1 and 2
Anti-pyretic, anti-inflamatory, analgesic: arthritis, gout
GI effects and CNS disturbances common
Avoid unless other NSAIDs ineffective
Sever heart failure, peptic ulceration
What is the benefit of oxicams? An example? Indication? Dosing?
Relatively COX-2 selective (10 fold) less GI irritation
Once daily due to long t1/2
What is diclofenac an inhibitor of? What is it's indication?
Long term tx of arthritis
Coxibs. Name two drugs. Selectivity COX1 or 2? Recommended use and why? Onset of action time for analgesia and anti-inflamation? Contraindications?
Selective COX-2, Lower risk of GI bleeding, no antiplatelet effect.
Low dose, for short duration if possible, risk of MI/stroke associated with long term tx. For patients who need NSAID but risk of GI toxicity.
Full analgesia 1 week, full antiinflammatory up to 3 weeks.
Ulcerative colitis, Crohn's disease - worsen bowel inflammation. Ischaemic heart disease, heart failure, vascular disease
Paracetamol. Uses (indications), mechanism, ADR, cautions, interactions?
Analgesic (regular use more effective than as required) antipyretic, (poor anti-inflammatory)
Probably inhibits PG synthesis in CNS by COX-3
Few at therapeutic dose
Hepatic impairment. Most common drug used in overdose.
Warfarin? may increase INR (unclear and contradictory evidence)
Where are opioid receptors found and what functions are they involved with?
Brain stem: respiration, cough, nausea, bp, pupil diameter
Spinal cord & thalamus: pain
Limbic system: emotional behaviour
Give examples of full agonists, pro-drugs and mixed agonist/antagonist & partial agonist. Indications?
Morphine, fentanyl, sufentanil
codiene (10% metabolised to morphine)
- Morphine = pain
- codeine = mild pain, coughing, diarrhoea
What is naloxone and what is it used for?
Opioid receptor antagonist
Used to reverse coma and respiratory depression after opioid overdose.