Definition of pKa of a Drug
pKa of a drug is the pH at which:
- 50% ionized, 50% non-ionized — Correct Answer
- 100% non-ionized
- 100% ionized
- 75% ionized, 25% non-ionized
Explanation:
Correct Answer: 50% is ionized and 50% is non-ionized
pKa of a drug is the pH at which 50% of the drug is ionized and 50% is non-ionized. It is a key parameter in the Henderson-Hasselbalch equation used to calculate the percent of drug in ionized form.
Clinical Relevance
- In monogastric animals with low stomach pH, weak acids (e.g. aspirin, pKa 3.5) are better absorbed from the stomach than weak bases — because weak acids exist mostly in non-ionized (lipid-soluble) form in acidic pH.
- Weak bases are better absorbed from the small intestine where pH is more alkaline.
- Only the non-ionized form is lipid-soluble and can cross membranes.
📚 About this Topic — Veterinary Pharmacology and Toxicology
This multiple choice question is from Veterinary Pharmacology and Toxicology, Veterinary Science. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Veterinary Pharmacology and Toxicology to strengthen your preparation.
