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ANALGESICS (Outline (Others (Gabapentin, Tramadol), NSAIDs, Local…
ANALGESICS
Outline
NSAIDs
Local anaesthetics
NMDA antagonists
Alpha-2 agonists
Others
Gabapentin
Tramadol
Local Anaesthetics
Pharmacodynamics
Mechanism of Action
Does not effect resting membrane potential
Interfere with action potential generation and noxious stimuli conduction
Act on voltage-gated sodium channels
Forms
Ionic form
Sodium channels
Unionised form
penetrate the nerve
Affect
Sensory n. before motor n.
Small n. before large n.
Myelinated n. before unmyelinated n.
More effective in fibres which are firing
inactivated Na channels
Types
Amide-linked
Characteristics
Heat stable
Can be stored for longer
Hepatic metabolism, renal excretion
Examples
Lidocaine
Suitable for IVRA
Bupivicaine
Dextro- isomer is cardiotoxic
Mepivicaine
Expensive
Less irritant
No preservative
Less vasodilation
Proxymetacaine
Rapid onset of activity
Ester-linked
Examples
Procaine
Cocaine
Characteristics
Easily broken down by esterases
Less stable
Para-aminobenzoates can cause allergic reactions
Pharmacokinetics
Absorption
weak bases
pKa
onset of action
PPB
duration of action
distribution
Lipid solubility
potency
Toxicity
CNS effects
repiratory depression
Tremors
Convulsions
Cardiovascular effects
Arrhyhtmias
Reduced myocardial contractility
Vasodilation
Hypotension
Others
Allergic reactions
Tissue irritation
Inadvertant i/v administration