Chapter 2 peripheral nervous system drugs - local anesthetics, injectable

Question 1

local anesthetics

Answer 1

• used for infiltration anesthesia (superficial method of inducing numbness for dental procedures, minor skin surgeries and similar procedures.)
• local nerve blocks
• spinal nerve blocks
• epidural nerve blocks

mechanism:
* prevents nerve conduction by reducing permeability of neuronal membrane to sodium (preventing na+ influx required for action potentials)

1) bicarbonate as an adjunct in local anestheisa
* added to local anesthetic preparations
* cna inc % of anesthetic in the nonionized form
* accelerating penetratio nof nerve sheath; once internalized, drug re-equilibrates to the cationic (active) form

2) preferential blockade of small nerve fiber
* pain and temperature fibers (A and C fibers) more easily penetrated by local anesthetics than larger ones
* order of loss nerve fx
1. pain
2. temperature
3. touch
4. proprioception
5. skeletal muscle tone

3) epinephrine as adjunct in local anesthesia
* vasoconstriction resposne to epinephrine causes — local hemostasis, inhibiting distrubtion of lcal anesthetic away from injection site, dec systemic absorption and prolong duration of action
* can cause transient tachycardia

4) consequences of IV injection
* oral numbness, light headedness, altered taste or tinnitus

Question 2

Lidocaine (xylocaine)

amides

Answer 2

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication –
* all types of injection
* topical anestheisa
* sedation
* arrhythmias
* intracranial HTN

undesirable effects
* drowsiness
* dizziness
* heart block
* arrhtyhmias
* hypotension
* myocardial depression

onset
* rapid (<1.5 min)
* epidural (5-15 min)

duration few hours (moderate)

pharmcokinetics -
* metabolized by mixed fx oxidases in liver; some metabolies are active
* excreted in urine

most frequently used

Question 3

Ropivacaine (naropin)

amides

Answer 3

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication –
* local or regional anesthesia for sugery
* post op pain
* obstetrical procedures (child birth related)

undesirable effect
* anxiety

onset
* rapid 1-5 min
* epidural 15-30 min

duration moderate long (few hrs to several hours)

pharmcokinetics -
* metabolized by mixed fx oxidases in liver; some metabolies are active
* excreted in urine

Question 4

bupivacaine (marcaine) (sensorcaine)

amides

Answer 4

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication
* local infiltration, lumbar, subarachnoid, caudal (tail vertebrae?), peripheral nerve, dental block
* long duration inc utilty for epidural block during abor

undesirable effects
** similar to lidocaine **

• drowsiness
• dizziness
• heart block
• arrhtyhmias
• hypotension
• myocardial depression

IV administration may induce ventricular arrhythmias

onset: slow 5 min or epidural 10-20 min)
duration long or several hours

pharmcokinetics -
* metabolized by mixed fx oxidases in liver; some metabolies are active
* excreted in urine

used when long duration desired

Question 5

mepivacaine (carbocaine, polocaine, isocaine)

amides

Answer 5

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication
* infiltration
* lnerve block
* epidural anesthesia
* dental infiltration

undesirable effects
* less drowsiness and amnesia than lidocaine

rapid epidural
5-15 min

moderate duration (few hours)

caution with use if have renal impairment

Question 6

prilocaine (citanest)

amides

Answer 6

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication
* local anesthesia
* nerve block or
* dental procedure - infiltration

undesriable effects
* similar to lidocaine

• drowsiness
• dizziness
• heart block
• arrhtyhmias
• hypotension
• myocardial depression
• methemoglobinemia (in large doses!) [Methemoglobinemia (MetHb) is a blood disorder in which an abnormal amount of methemoglobin is produced. Hemoglobin is the protein in red blood cells (RBCs) that carries and distributes oxygen to the body. Methemoglobin is a form of hemoglobin.

With methemoglobinemia, the hemoglobin can carry oxygen, but is not able to release it effectively to body tissues.]
* causing cyanosis, pallor, fatigue, weakness, headache, central nervous system depression, metabolic acidosis, seizures, dysrhythmias, coma, and death.
* distinctive shade of blue or purple.

• onset – rapid (< 2 min), epidural (5-15 min)

duration - short

Question 7

procaine (novocaine)

ester

Answer 7

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication
* low potency
* infiltration and spinal anesthesia

undersirable effects
* low toxicity

rapid epidural 15 -25 min
short duration 15 - 60 min

pharmacokinetics
* metabolized by plasma cholinesterase
* metabolite (p-aminobenzoic acid — may cause hypersensitivity

Question 8

chloroprocaine (nesacaine)

ester

Answer 8

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication
* low potency
* infiltration, nerve block, and epidural anesthesia

undesirable effects
* permanent neural damage may result from use of this agent for SPINAL anesthesia

moderate epidural (5-15 min)
short (30-90 min)

pharmacokinetics
* metabolized by plasma cholinesterase
* metabolite (p-aminobenzoic acid — may cause hypersensitivity

preferred for those susceptible to malignant hyperthermia

Question 9

tetracaine (pontocaine)

ester

Answer 9

• ionized form of drug temporarily reduces permeaibliyt of neuronal membranes to sodium; RESULT - no action potential generates or propogates

indication
* high potency (need small amount)
* spinal anesthesia

undesirable effect
* most toxic ester

slow epidural (20-30 mins)
moderate (few hrs?) duration

pharmacokinetics
* metabolized by plasma cholinesterase
* metabolite (p-aminobenzoic acid — may cause hypersensitivity

motor blockade lasts longer than sensory