Question

Itraconazole is a drug with pKa of 3.8 . What would be the precent of ionized of this drug in the stomach at pH 1.87?

A) 1%
B) 9%
C) 99%
D) 91%

Answer 1

The percent ionization of itraconazole in the stomach at pH 1.87 is approximately A) 1%.

Step-by-step explanation:

To calculate the percent ionization of itraconazole at a specific pH, we need to compare the pH to the drug's pKa. When the pH is below the pKa, the drug is mostly in its protonated form and therefore less ionized. When the pH is above the pKa, the drug is mostly in its ionized form. In this case, the pH of the stomach (1.87) is lower than the pKa of itraconazole (3.8), so we can expect a low percentage of ionization.

According to the Henderson-Hasselbalch equation, the percent ionization of a weak acid can be calculated using the following formula:

Percent ionization = (10^pH / (10^pH + 10^pKa)) x 100%

Substituting the given values into the equation, we get:

Percent ionization = (10^1.87 / (10^1.87 + 10^3.8)) x 100%

Calculating this expression, we find that the percent ionization of itraconazole in the stomach at pH 1.87 is approximately 1%.