Question

Rank the following LAs according to their degree of ionization at physiologic pH:

a) chloroprocaine
b) tetracaine
c) bupivacaine
d) lidocaine
Most to least ionized:
a) d, b, c, a
b) c, a, d, b
c) b, c, d, a
d) a, b, c, d

Answer 1

The ionization degree of local anesthetics such as chloroprocaine, tetracaine, bupivacaine, and lidocaine at physiological pH is determined by their pKa values and the Henderson-Hasselbalch equation. A solution of novocaine is basic, but exact values of [H3O+], [OH-], and pH cannot be calculated without the concentrations.

Step-by-step explanation:

When considering the local anesthetics (LAs) and their degree of ionization at physiological pH, it is important to remember that the more basic the compound (i.e., the higher the pKa), the less ionized it will be at a lower pH, such as the physiological pH of 7.4. For local anesthetics, the pKa is usually slightly above 7.4, and the proportion of ionized to non-ionized form is determined by the Henderson-Hasselbalch equation. The order of these compounds from most to least ionized at physiological pH is based on their pKa values; however, without these values provided, we cannot definitively rank chloroprocaine, tetracaine, bupivacaine, and lidocaine.

To answer the question pertaining to novocaine, since novocaine (or procaine) is a weak base, its solution would be basic in nature. Given the ionization constant of procaine (Kb = 7 x 10-6), we can assume that it doesn't ionize significantly. However, without the exact concentrations, calculations for [H3O+], [OH-], and pH cannot be precisely provided in this response.