Weak Acids and Weak Bases Flashcards
When does a drug usually precipitate?
FYI: nonionized drugs are usually lipid soluble and penetrate BBB and placental barrier; ionized drugs are typically water soluble;
So, if you have a drug dissolved in water and its mostly in the nonionized form, it is likely that the drug will precipitate
Weak acids become more ________ when pH decreases and more _______ when pH increases.
nonionized, ionized
ex) pKa of thiopental = 7.6–> if put into pH of 7.4, since thiopental is a weak acid and it was placed into a slightly more acidic environment than it’s pKa…. more of the injected thiopental will be in the nonionized form
Weak bases become more ________ when pH decreases and more _______ when pH increases.
ionized, nonionized
What is pKa?
when the pH of the aqueous solution is the same as the pKa of the drug, the drug will be 50% nonionized and 50% ionized.–> PKa is the pH at which the drug reaches 50%/50% equilibration, not whether or not it is an acid or a base.
What are classic weak acids found on board exam?
thiopental and other barbiturates; propofol
Weak acids give up ______, but not completely.
H+
Acid + Acid = ________
nonionized; weak acids become more nonionized as pH falls (H+ increases)
Strictly speaking, the nonionized form of the weak acid is the _____, and the ionized form is called the ______.
acid, conjugate base
The _____ the pKa of a weak acid, the ______ the amount of drug in nonionized form at physiological pH (7.4).
greater; greater
Should thiopental be mixed with a low pH solution?
No. b\c it is a weak acid and when placed in an acidic solution more of the drug becomes non-ionized–> nonionized will form precipitate
Why is thiopental stored and placed in a solution with pH 10-11?
when it is stored in a solution with a pH of 10-11, most of the drug will be in ionized form—> ionized drug is highly water soluble–> precipitate will not form when thiopental is stored in a solution with a high pH
Name 4 of the primary weak bases seen on the board exam.
1) local anesthetics
2) ketamine
3) opioids
4) benzo’s
Weak bases accept _______, but never do so completely.
hydrogen ions (H+)
Weak bases become more ________ as pH increases.
non-ionized as H+ decreases
Base + Base = ________
nonionized
EX) pKa of lidocaine is 7.7; if pH is 7.7, 50% of the lidocaine would be in the ionized form and 50% in the nonionized form–> when lidocaine is injected into the body at pH=7.4, less than 50% of the drug will be nonionized (base + acid=ionized)
