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17 Cards in this Set

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Local anesthetics
An agent that reversibly blocks electrical activity of excitable tissues
Structure of L.A.
All have an aromatic end (lipohilic) and an amino end (hydrophilic)
Mech of Action of L.A.
- The hydrophilic site can bind to an open Na+ channel and blocks Na+ transport into the neuron =>dec neuronal conduction rate, dec depolarization, and inc refractory period
- Since the effect is on open chanels it is greatest on rapidly firing cells
Which nerves are affected by L.A.
Smaller fibers>larger fibers
Myelinated neurons
High firing rate
Pain>cold>warm>touch>motor
L.A. w/ __linkages have shorter durations and L.A. w/ __linkages have longer durations
Ester (bond is broken by plasma cholinesterase); amide (metabolized by P450)
T/F L.A. are weak bases
True; not as effective against infected tissues since infections lower tissue pH
T/F Repeated use of an epidural anesthetic can lower pH and cause tachyphylaxis
True
L.A.- Esters (3)
1- Cocaine: Opthalamic or nasal surgery; a vasoconstrictor; can have CNS SE
2- Benzocaine: Topical, low solubility & absorption; long duration
3- Procaine: Short T.5; never use topically
L.A.- Amino Amides (8)
1- Procainamide: Oral/IV for arrhythmias; Lupus-like symptoms; doesn't enter CNS
2- Lidocaine: Topical or injected;
SE tremors, slurred speech, dizziness, drowsiness
3- Articaine: Paraesthesia
4- Mepivacaine: Used w/o epi
5- Bupivacaine: Long duration
6- Prilocaine
7- Ropivacaine
8- Etidocaine
SE of L.A.
- CNS: Disorientation, drowsiness, slurred speech, tinnitus, and eventually CNS excitation
- Cardiovascular: Altered heart rhythms
- Allergic rxn: Occur more frequently w/ esters
Special cases for L.A.
1- Tetrodotoxin: Irreversible Na+ channel blocker
2- Saxitoxin:" "- red tide; respiratory paralysis
Spasticity
Muscle hypertonia
Tx of spasticity
Altering innervating neurons or directly inhibiting skeletal muscle
Baclofen
Antispastic- neuronal
- Oral GABAergic drug; activates receptor
- Inc inhibitory spinal cord neurons
- May cause ataxia
Diazepam and other benzos
Antispastic- neuronal
- Activate GABAergic receptors
Tizanidine
Antispastic-neuronal
- Orally active alpha 2 agonist
- Inhibits neurons
- SE: hypotension
- D. botox: MoA => inhibits ACh release
Dantrolene
Antispastic- muscle
- Orally active
- Inhibits Ca2+ release from sarcoplasmic reticulum from skeletal muscle
- SE: muscle weakness