The Correct Answer is C
“Those anesthetic agents that have a high pKa will have few molecules present as the free base (lipid-soluble form) at normal tissue pH (7.3 to 7.4). Therefore the anesthetic quality will be poor since an insufficient number of free-base molecules are present.
Conversely those anesthetic agents with a very low pKa provide a large number of free-base molecules to diffuse through the neural sheath. However, this agent, too, would be relatively ineffective since very few base molecules would dissociate to the cationic form, the one necessary for attachment to the specific receptor site.....
In contrast to alkaline conditions, a low tissue pH, as found in infected areas (pus has a pH of 5.5 to 5.6), may interfere with the development of adequate anesthesia by preventing deprotonization and liberation of the free base.
The potential action of all local anesthetics depends on the ability of the anesthetic salt to liberate the free alkaloid base....”
pKa’s of local anesthtics:
- mepivicaine 7.6
- lidocaine 7.9
- bupivicaine 8.1
“a” is incorrect as bupivicaine actually has a HIGH lipid solubility
“b” is incorrect as lidocaine has an average--to low dissociation constant
“d” is incorrect as mepivicaine has average protein binding when compared to the other anesthetic agents
“ e” is incorrect as high potency has to do with protein binding and not pKa or pH.
Monheim’s Local Anesthesia and Pain Control in Dental Practice, Bennet C. Richard, Seventh Edition, 1984, pp.125-159
(Remember that... IOCAINE POWDER .....comes from Australia and is odorless, colorless, and tasteless!!)
0 comments:
Post a Comment
Please Leave your take on these notes and mcqs. Your feedback is much appreciated.