Prilocaine

9 01 2013

Did my first Bier’s block yesterday. unwitnessed fall in a lady (high care nursing home patient) with significant comorbidities : COPD and newly diagnosed malignancy.

I’ve done them twice at least with senior registrars (me being the lever or the counter-traction guy) during the manipulation.

Yesterday was a first adjusting the cuff etc (but the boss still insisted on giving the drug himself)

biers_block —this is a page pdf file produced by the Gold Coast hospital which serves as a good intro and explanation including step by step about the Bier’s block. More goodies from : emergencyweb.net (you need to register – FREE)

Addit as of Dec 2012, the Gold Coast Hospital has limited the access to emergencyweb.net to only their staff.

So….drug of choice we gave was : PRILOCAINE

Let’s talk about local anaesthetics with Prilocaine as our star drug

WHAT is it ?

Local anaesthethic. Amide type

PHARMACOKINETICS

  • Absorption : systemic absorption affected by :
  1. dosage
  2. site of injection – high vascular area e.g. trachel mucosa means rapid absorption ; peak serum level highest esp intercostal block while sciatic and femoral lowest
  3. drug-tissue binding
  4. local tissue blod flow
  5. use of adrenaline (vasoconstrictor)
  • Distribution :
  1. Localised >>>
  2. Systemic …2 compartment model : initial alpha phase – rapid distribution and highly perfused organs. Slower beta phase – less perfused tissue ( muscle/gut) protective effect by uptake in lungs – serves to attenuate arterial concentration.
  • Metabolism
  1. amides converted to water soluble metabolites in liver

PHARMACODYNAMICS

  • Mechanism of Action
  1. Membrane potential – blockade of voltage-gated sodium channels
  2. Sodium channel isoforms
  3. Channel blockade
  4. Other effects :
  • Structure activity characteristics of Local Anaesthetics
  1. smaller + more lipophilic LAs, faster rate of interaction w sodium channel R
    —-lignocaine/procaine/mepivacaine more water soluble than tetracaine/bupivacaine/ropivacaine (more potent and have longer duration, also bind more ext to proteins)

 

  • Neuronal factors affecting block
  1. differential block

Amides vs esters. Usual questions in MCQ for the primary ?which is a amide or ester ?

local anaesthetics that are Esters :have just one ” i ” in their names eg procaine ,cocaine but …
Amides : have more than one ” i ” in their names lidocaine, bupivacaine,prilocaine


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