Local Anesthetics Pharmacology Questions And Answers With Latest Quiz
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Course
Local Anesthetics
Institution
Local Anesthetics
Local Anesthetics Pharmacology Questions And Answers With Latest Quiz
What is the chemical structure of most local anesthetics? ANS Most consist of a lipophilic group (frequently an aromatic ring) connected by an intermediate chain (commonly including an ester or amide) to an ionizable group (usu...
Local Anesthetics Pharmacology Questions And
Answers With Latest Quiz
What is the chemical structure of most local anesthetics? ANS Most consist of a lipophilic group
(frequently an aromatic ring) connected by an intermediate chain (commonly including an ester or
amide) to an ionizable group (usually a tertiary amine).
Do amide or ester local anesthetics have a shorter duration of action? ANS Since ester links (as in
procaine) are more prone to hydrolysis than amide links, *esters usually have a shorter duration of
action*.
Why are many local anesthetics sold as hydrochloride salts? ANS They are weak bases marketed
as water-soluble salts (hydrochlorides) because the *hydrochloride salts are mildly acidic, which
increases the stability of the local anesthetic* esters and any accompanying vasoconstrictor
substance.
How does pH and charge play into the effectiveness of local anesthetics? Why do infected tissues
respond poorly to local anesthetics? ANS Most local anesthetics have a pK of 8-9, so *the largest
fraction at physiologic pH will be the cationic form*. The cationic form is the most active form at the
receptor site, but the uncharged form is required for rapid penetration of the cell membranes (the
anesthetic receptor is not accessible from the external side of the cell membrane). Ergo, local
anesthetics are much less effective in infected tissues because *these tissues have a low extracellular
pH, so that a very low fraction of nonionized local anesthetics is available for diffusion into the cell.*
Why are local anesthetics often administered with a vasoconstrictor like epinephrine? ANS The
duration of action of a local anesthetics is proportional to the time during which it is in contact with
nerve. *Epinephrine reduces systemic absorption of local anesthetics from the depot site by
decreasing blood flow in these areas*, which is important for drugs with short durations of action. It
also *prevents the toxic effects of systemic absorption*.
Which factors affect the systemic absorption of local anesthetics? ANS • Dosage
• Site of injection
• Drug-tissue binding
• Presence of vasoconstrictors
• Physicochemical properties of the drug
, How does vascularization affect the absorption of a local anesthetic? ANS Application of a local
anesthetic to a highly vascular area (tracheal mucosa) results in more rapid absorption and thus
higher blood levels than if it had been injected into a poorly perfused area (tendon, dermis or
subcutaneous fat).
Why is epinephrine used in spinal anesthesia? ANS Epinephrine *directly enhances and
prolongs* anesthesia by *acting on α2-adrenoceptors, which inhibit release of substance P and
reduce sensory neuron firing.* Recognition of this fact has led to the use of *the α2 agonists
clonidine and dexmedetomidine to augment local anesthetic effect* in the subarachnoid space and on
peripheral nerves.
What happens if an adjuvant vasoconstrictor given with a local anesthetic reaches systemic
circulation? ANS There may be delayed wound healing, tissue edema, or necrosis after local
anesthesia due to *increased oxygen consumption of the tissue* (via sympathomimetic amines); this,
together with vasoconstriction, leads to *hypoxia and local tissue damage*.
Why don't you use vasoconstrictors with local anesthetics in hand or foot surgery? ANS The use
of local anesthetics containing vasoconstrictors during surgery of the digits, hands or feet resulting in
prolonged constriction of major arteries in the presence of limited collateral circulation could
produce irreversible hypoxic damage, tissue necrosis and gangrene.
How are ester-linked local anesthetics metabolized? ANS Ester-linked local anesthetics are
metabolized by tissue and plasma esterases (pseudocholinesterases). This process is fast and the
resulting metabolites are excreted by the kidney.
How are amide-linked local anesthetics metabolized? ANS The amide-linked local anesthetics
are in general degraded by liver cytochrome P450 enzymes. The three major routes of hepatic
metabolism are aromatic hydroxylation, N-dealkylation and amide hydrolysis. Metabolites are
excreted by the kidney.
What is the mechanism of action of local anesthetics? ANS Local anesthetics *block voltage-
gated sodium channels by binding the receptors near the intracellular end of the channel* and
blocking the channel.
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