Drug A is a weakly basic drug with a pKa of 7.8. If administered orally, at which of the following sites of absorption will the drug be able to readily pass through the membrane?

A. Mouth (pH approximately 7.0)
B. Stomach (pH of 2.5)
C. Duodenum (pH approximately 6.1)
D. Jejunum (pH approximately 8.0)

CHECK ANSWER

The correct answer is D. Jejunum (pH approximately 8.0)

Because Drug A is a weakly basic drug (pKa = 7.8), it will be predominantly in the nonionized form in the jejunum (pH of 8.0). For weak bases, the nonionized form will permeate through the cell membrane readily.