Pharm I, Local Anesthetics
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Benefits of Systemic Lidocain (3):
- Central Analgesic Effect (Blocks Na channel in central nociceptive neurons)
- Prokinetic (GIT)
- Antioxident/Inflammatory modulators
Used appropiately, Local Anaesthetics provide ____ analgesia
Local Anasthetics are classified as:
Most common Amide LA's (3):
Most common Ester LA's:
Tetracaine is often used for...
Ester Vs Amide LA (1/2 Life and stability):
- Ester= unstable, 1/2 life is a few mins
- Amides= Stable, 1/2 life is a few hours
LAs are transported in the plasma, and are bound to _____& ____. The ____ is active
- Alpha Glycoproteins
- Albumin (minimally)
- Unbound drug
What property affects the potency of LA's
Increasing Lipid Solubility
What property affects the duration of action of LAs
What property affects the rapidity of onset of LAs?
Low pKa= Rapid onset
What LA's have a rapid onset?
Rate of Diffusion is dependent on (4):
- pKa of Drug
- pH of nerve
- Amount of LA
- Vascular Removal
Successful impulse blockade is dependent on
- Sufficient concentration of anesthetic within and along axon
- Na/K channel density
- Na/K channel susceptibility
As a rule of thumb, ________, the greater concentration of LA required to produce blockade
the greater the diameter of nerve fiber
Which neuron type is unmyelinated?
How does dosage affect an anasthetic block?
- Rapidity of Onset
How does volume affect an anasthetic block?
- Dermatomal Distribution of neural blockade
- DOES NOt DETERMINE SPEED OF ONSET, INTENSITY, OR DURATION
How does pH affect an anasthetic block?
The closer the pKa to physiological pH, the better it penetrates the membrane
How can pH of LA be alkalinized?
Add Sodium Bicarbonate
Repeated blocks can cause...
Tachyphylaxis, especially when pH ~pKa
Local Anesthetic Side Fx Occur when...
high plasma concentrations are achieved
LA plasma concentrations are determined by (6):
- Rate of Absorption
- Acid-Base Status
- Rate of Metab
- +/- Epi
Lidocaine TOXIC dose, IV:
Never give more than ___mg/kg Lidocaine IV
Bupivicaine TOXIC dose, IV:
Never give more than ___mg/Kg Bupivicaine IV
What must be considered when combining local anaesthetics?
Toxicity of each is additive
CNS effects of LA OD (2)
- CNS Depression
- Followed by Agitation, Muscle Twitching and convulsions
Cardiovascular Effects of LA OD (2):
- Myocardial Depression (Bradycardia and Decreased CO)
Which is harder to tx Lidocaine or Bupivacaine OD? Why?
Bupivacaine- High binding affinity for cardiac myocytes (70x)
Tx for a Local Anesth OD(5) :
- Treat Sympotoms
- Seizures= Valuim PRN
- Cardiovascular= Fluids, O2, Ionotropes, Antimuscarinics if Bracycardic
Precautionary steps to avoid Local Anest OD (4)
- Caution w/ small animals
- Double check weight
- Diltute LA
- Draw back before injecting
Which LA has antiarrhythmic properties?
Which LA is more potentially cardiotoxic?
Bupivacaine (cardiotoxic before neurotoxic)
Which LA is used for nerve blocks in horses?
Less irritating alternative to Lidocaine
Benefits of using Ropivicaine over Bupivacaine (5):
- Longer Duration
- Less Cardiotoxic
- Less Arrythmogenic
- Selective for Sensory Nerve Fibers (over A alpha motor fibers)
- Dissociates more rapidly from Na channels (less accumulation)
Which LA has a longer duration of action than Lidocaine?
Bupivicaine (2-6 hours)
Which LA is a more potent alternative than Lidocaine?
Which LA can cause tachyphylaxis?
What is a safer alternative to Xylocaine spray in cats?
2% Lidocaine WITHOUT adrenaline, spray directly on Vocal Cords
Rec Dosage for: Lidocaine, Mepivicaine, Bupivacaine & Ropivicaine
- Lidocaine: 4mg/kg, but 2mg/kg is sufficient
- Mepivacaine: 4mg/kg, but 2mg/kg is sufficient
- Bupivacine: 2mg/kg
- Ropivacaine: 2mg/kg
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