Pharm Test 3: CH 26
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blocking impulse along axons by blocking sodium channels
prototype agents for local anesthetics
provaine (novocaine), lidocaine, and cocaine
2 major groups of anesthetics:
esthers and amides
esther type anesthetics
procaine (novocaine), contain an esther linkage in their makeup
contain an amide link, lidocaine (xylocaine)
esther and amide differences (2):
method of inactivation and promotion of allergic response
nonmyelinated neurons are blocked easier than myelinated neurons
thats why some sensations can be blocked earlier than others
developed in 1905, what is the prototype for esthers?
- administered IM (1%,2%,10%)
- dentists "favorite"
- greater risk for allergic reactions
greater risk for allergic reactions
list of esthers
procaine (novocaine), chloroprocaine (nesacaine), tetracine (pontocaine)
injectable list of amides
- lidocaine (xylocaine, octocaine)
- articaine (septocaine)
- bupivacaine (marcaine, sensorcaine)
- mepivacaine (carbocaine, polocaine)
- prilocaine (citanest)
- ropivacaine (naropin)
topical list of amides
- dibucaine (nuercainal)
- lidocaine (xylocaine, lididerm,others)
topical list of esters
- benzocaine (many names)
- cocaine (generic only)
- tetracine (generic only)
"other" topical local anesthetics
- dyclonine (sucrets)
- pramoxine (tronothane, others)
introduced in 1948, I am the prototype for amide-agents. I am one of today's most widely used local anesthetics. I can be administered topically or by injection. I am rapid, intense and more prolonged with an equal dose of procaine. Epi is my friend and helps me stick around longer. I don't really cause allergic reactions and people with an allergy to an esther aren't cross-allergic to me. I can cause CNS and cardiovascular toxicity. The liver inactivates me. I am used in local anesthesia and dysrhythmias-by suppressing cardiac excitability by blocking sodium channels. Which medicine am I?
- available in cream, ointment, jelly, solutions, aerosol, patch for topical administration
- injection available in concentrations ranging from .5-2%. some injectibles contain epi
I was the first local anesthetic. I was initiated by Freud & Koller in 1884. I am an esther type. I block uptake of norepi by adrenergic neurons causing sympathetic and CNS effects. Administered topically I am used on the ear/nose/throat. My anesthetic effects last about an hour. I cause intense vasoconstriction by blocking norepi at sympathetic terminals on blood vessels. I am inactivated by plasma esterases and liver enzymes. My CNS effects are euphoria. loquaciousness, reduced fatigue and increased sociability and and alertness. In excess I can cause seizures and even death. I cause psychological dependence and am considered a schedule 2 drug. I can stimulate the heart and constrict blood vessels by stimulating the sympathetic nervous system and block norepi uptake in the peripheral. In this case I can give tachycardia or even dysrythmias. I am prepared as powder and in solution topically, usually at 4%. who am I?
srface anesthesia is accomplished by applying anesthetic how?
directly to the skin or mucous membranes
agents most employed for topical administration are:
lidocaine, tetracaine, cocaine
therapeutic uses of topical anesthesia:
- relieve pain, itching, soreness from infection, thermal burns, sunburn, diaper rash, wounds, bruises, abrasions, plant poisoning, insect bites.
- aplication may be to mucous membranes of the nose,mouth,pharynx,larynx, trachea, bronchi, vagina and urethra. also for hemorrhoids, anal fissures and pruritus ani.
systemic toxicity of topical anesthetics:
- cardiovascular and CNS are principal concerns. absorption is related to surface area.
- an IV line should be in place to be ready to treat toxicity.
- application to mucus membranes poses greatest risk
- monitor for cardio, repiratory and state of conciousness
administration of anesthetics by injection:
- must be done by anesthesiologist
- have resuscitative equipment available because of risk for compromise
- IV line should be in place to reverse effects rapidly
- aspirate before injection to ensure not in a vein or artery- toxicity if in vessel
inject local anesthetic directly into immediate area of surgery or manipulationcan be prolonged by combining with epi (except for areas with ende arteries such as toes, fingers, nose, ears ,penis-decrease blood flow can lead to gangrene)most common used are lidocaine bupivacaine
injecting anesthetic into or near nerves that supply surgical field but at a distal siteadvantage of producing anesthesia with doses that are smaller than needed for infiltrationdrug selection based on required duration of anesthesiashort procedures- lidocaine, mepivacainelong procedures- bupicavaine
nerve block anesthesia
used to anesthetize extremities- hands, feet, arms, lowe legs; not entire leg because too much anesthetic would be neededanesthesia produced by injecting to distal vein- blood is removed from limb by gravity or esmarch bandage and tourniqet applied then injection to prevent systemic circulation (double tourniquet used for arterial blood flow)lidocaine without epi is preferred methodonce tourniquet is released only 15-30% is released systemically
IV regional anesthesia
acheieved by injecting into epidural spave (in spinal column but outside dura mater)
catheter placed into epidural space allows administration by bolus or continuous infusion
diffuses into subarachnoid space and blocks nerve conduction int he spinal cord itself
can reach systemic circulation in significant amounts
used during delivery-neonatal depression may occur
licocaine and bupivacaine
concentrated bupivacaine must not be used in obstetric pts because of risk for cardiac arrest
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