3 pH and Drug movement Ngu

Question 1

Review the Le Chatelier’s Principle of Equilibrium

Answer 1

At equilibrium if a product or substrate is removed or added the reaction will shift so as to reach a new equilibrium

for weak acids
H+ + A- = HA

for weak base
HB+ = B + H+

Question 2

Calculate the dissociation of weak acid and weak base drugs given pH and pKa.

Answer 2

Using the pH formula as follows:
log(XH/X) = pKa - pH

we can take the find % protonated or unprotonated by taking the XH(prot) or X(unprot) value and dividing by XH+X value

note: X stands for Base or Acid depending on what is being asked

Question 3

Predict the ratio of drug partitioning into body compartments of known pHs using the Henderson-Hasselbach equation.

Answer 3

Using the H-H equation to find out what % of drugs are protonated and not and thus leading to whether it will move out of the circulatory system

Question 4

Manipulate the pH of a body compartment to achieve a therapeutic goal given a drug’s pKa.

Answer 4

using the pKa of the drug as a starting point

weak acid drugs will be more likely in a nonpolar form in a more acidic environment

weak base drugs will be more likely in a nonpolar form in a more basic environment