Pharmacrystal

www.pharmacrystalniper.blogspot.com

www.pharmacrystalniper.blogspot.com

8

Pharmacokinetic Principles: pH and Drug Movement

1) Most drugs are either ____ acids or ____ bases.
       a) Strong; Strong
       b) Strong; Weak
       c) Weak; Weak
       d) Weak; Strong
2.1) Aspirin readily donates a proton in aqueous solutions and pyrimethamine readily
accepts a proton in aqueous solution. Thus, aspirin is a(b) ____ and pyrimethamine is
a(n) ____.
       a) Acid; Base
       b) Base; Acid
       c) Acid; Acid
       d) Base; Base
2.2) Given the equilibrium HA <=> A- + H+ (acid) and BH+ <=> B + H+ (base), in an
acid environment (low pH) the acid reaction will move to the ____ and the base reaction
will move to the ____.
       a) Right; Left
       b) Right; Right
       c) Left; Right
       d) Left; Left
3.1) What form of a drug is more lipid-soluble, and thus would remain trapped within a
compartment where the pH does not favor the lipid-soluble form?
       a) Strong acid (A-)
       b) Weak acid (A-)
       c) Neutral (AH and B)
       d) Weak base (BH+)
       e) Strong base (BH+)
3.2) The lipid-soluble form of a base is ____ and the lipid-soluble form of an acid is
____.
       a) Protonated; Protonated
       b) Protonated; Unprotonated
       c) Unprotonated; Unprotonated
       d) Unprotonated; Protonated

4.1) If the pKa of Aspirin (acetylsalicylic acid) is 3.5 and the pH of the stomach is 2.5,
how much Aspirin is in the protonated species in the stomach and is this the amount
available for absorption?
         a) 

≈ 

91%; Yes

         b) 

≈ 

91%; No

         c) 

≈ 

9%; Yes

         d) 

≈ 

9%; No

4.2) What percentage of Aspirin would be ionized in the blood compartment (pH = 7.4)
assuming pH is 7.5 and Aspirin pKa is 3.5?
         a) (10,000 - 1) / 1 = 99.99%
         b) (100 - 1) / 1 = 99%
         c) None
         d) 1 / (100 - 1) = 0.9%
         e) 1 / (10,000 - 1) = 0.009%