Exam 1 Drugs: Local Anesthetics (16)

Question 1

Procaine

Answer 1

• Ester-linked
• short acting, more polar (rapid circulation removal)
• parental duration w/o epi is 15-30 mins, with epi is 30-90 mins
• low potency
• degraded by plasma esterases, metabolites excreted in urine
• small Vd
• clinical app: infiltration anesthesia for dental procedures
• adverse: cardiac arrest and hypotension from excessive systemic absorption, CNS depression or excitation, resp arrest, contact dermatitis
• contra: none
• excess PABA (metabolite) can reduce effectiveness of sulfonamides (PABA also an allergen)

Question 2

2-Chloroprocaine

Answer 2

• ester-linked
• short acting homologue of Procaine
• rapidly hydrolyzed by plasma esterases, metabolites excreted in urine
• clinical app: obstetrical anesthesia given epidurally before delivery
• adverse: cardiac arrest and hypotension from excessive systemic absorption, CNS depression or excitation, resp arrest, contact derm
• contra: use epidural with extreme caution in patients with neurological disease, spinal deformities, septicemia, or severe hypertension
• PABA (metabolite) can reduce effectiveness of sulfonamides (PABA also an allergen)

Question 3

Tetracaine

Answer 3

• ester-linked
• long acting, high hydrophobicity (remains in tissues surrounding nerve for a long time, also makes metabolism slow b/c takes place in bloodstream)
• high potency (prolonged interaction w/ sodium channel)
• clinical app: topical and spinal anesthesia
• adverse: cardiac arrest and hypotension from excessive systemic absorption, CNS depression or excitation, resp arrest, contact derm, ALSO keratoconjunctivitis
• contra: localized infection @ site of topical application
• do not inject large doses in patients w/ heart block

Question 4

Proparacaine

Answer 4

• ester-linked
• duration of action inversely dependent on vascularity of tissue (longest: normal cornea, shortest: inflamed conjunctiva)
• clinical app: ocular anesthesia
• applied drop by drop
• used in those sensitive to amino ester LAs, less irritating during administration
• contra: cardiac arrest and hypotension from excessive systemic absorption, CNS depression or excitation, resp arrest, contact derm, ALSO keratoconjunctivitis
• contra: localized infection @ site of topical application
• do not inject large doses into those with heart block
• less antigenic than other benzoates

Question 5

Cocaine

Answer 5

• Ester-linked
• first LA, only naturally occurring LA
• medium duration of action (1-2 hrs topical or parenteral)
• medium potency (1/2 lidocaine)
• hydrolyzed by plasma esterases and tissues; excreted by kidney
• clinical app: mucosal and ophthalmic local anesthetic; diagnosis of Horner’s Syndrome pupil
• marked vasoconstrictive action (inhibits catecholamine reuptake)
• adverse: CNS excitation, convulsions, cardiac arrythmias, hypertension, stroke, cardiotoxic potential
• contra: hypersensitivity to cocaine-containing products
• cardiotoxicity and euphoria/addiction limit value as LA

Question 6

Lidocaine

Answer 6

• Amide-linked
• most commonly used LA
• moderate hydrophobicity (moderately potent)
• rapid onset of action, medium duration (1-2 hrs)
• low PkA allows for rapid diffusion through membranes (large amt in neutral form at phys pH)
• initially vasoconstricts but then vasodilates so need epi to prolong duration of action
• clinical uses: infiltration anesthesia, peripheral nerve block, epidural, spinal, topical anesthesia, class I anti-arrhythmic
• blocks sodium channels in cardiac myocytes
• metabolism by liver P450s, metabolites only weak anesthetic activity
• common adverse: CNS excitation
• contra: hypersensitivity to amide-linked LAs
• toxic effects mainly CNS and heart: drowsiness, tinnitus, twitching, seizures
• CNS depression and cardiotoxicity occur at high plasma levels

Question 7

Prilocaine

Answer 7

• Amide-linked
• very similar to Lidocaine
• rapid onset of action, medium duration (1-2 hours)
• high volume distribution
• has vasoconstrictive activity, does not require epi
• clinical app: dental infiltration and nerve block
• adverse: CNS excitation
• contra: hypersens to amide-linked LAs
• good choice for those w/ hypersens to epi

Question 8

Bupivacaine

Answer 8

• Amide-linked
• long duration of action
• highly hydrophobic, highly potent
• clinical app: infiltration, regional, epidural, spinal anesthesia; symp nerve block
• mostly used for labor and post-op anesthesia (also long dental procedures)
• more effect on nocioceptors than locomotion
• used at low concentrations because cardiotoxicity at high
• 2-3 hours pain relief w/o motor blockade
• metabolized in liver
• adverse: CNS excitation and cardiotoxicity
• contra: local infection at site of anesthesia, contra for use in spinal anesthesia with presence of septicemia, severe hemorrhage, shock, or arrhythmias
• blocks cardiac myocyte sodium channels during systole: can trigger arrhythmias
• R and S antiomers have diff affinities for sodium channels and diff CV effects

Question 9

Levobupivacaine

Answer 9

• Amide-linked
• S-antiomer of bupivacaine
• causes less vasodilation, so longer duration of action
• less potent, less cardiotoxic

Question 10

Ropivacaine

Answer 10

• Amide-linked
• long duration of action (4 hours)
• clinical app: management of acute pain (post-op, labor); for production of local or regional anesthesia for surgery
• adverse: hypotension, CNS excitation
• contra: known hypersens to ropivacaine or any LA of amide-type
• may have less cardiotoxicity than bupivacaine

Question 11

Articane

Answer 11

• Amide-linked
• rapidly metabolized (partially by cholinesterases in plasma, also liver)
• this minimizes potential toxicity
• clinical use: largely in dental anesthesia, also epidural, spinal, and regional anesthetic
• adverse: CNS excitation
• infection at site of injection (esp lumbar puncture), also shock

Question 12

Pramoxine (Pramocaine)

Answer 12

• topical
• skin or hemorrhoid pain relief
• OTC
• few reported side effects

Question 13

Dibucaine

Answer 13

• topical
• skin or hemorrhoid pain relief
• OTC
• adverse: redness, irritation, swelling, stinging or pain @ affected area

Question 14

Dyclonine (Dyclocaine)

Answer 14

• topical
• used to treat throat pain
• OTC
• adverse: irritation, stinging

Question 15

TAC

Answer 15

• mix of Tetracaine, Adreneline (Epi), and Cocaine
• sometimes used before suturing cuts
• concern about cocaine toxicity and addiction
• now use EMLA

Question 16

EMLA

Answer 16

• Eutectic mixture of lidocaine and prilocaine
• delivered topically as cream or patch
• higher concentration of LA/ drop contacting skin
• clinical app: venipuncture, arterial cannulation, and lumbar punctures. also dental procedures for children who dread pain of injections