## **Core Concept**
The bioavailability of a drug is a measure of the fraction of an administered dose of unchanged drug that reaches the systemic circulation and is one of the principal pharmacokinetic properties of drugs. It is influenced by factors such as absorption, hepatic first-pass metabolism, and solubility. The hepatic extraction ratio is a critical factor in determining the bioavailability of a drug, especially for drugs that undergo significant first-pass metabolism.

## **Why the Correct Answer is Right**
The bioavailability (F) of a drug can be calculated using the formula: F = f_a * (1 - E_h), where f_a is the fraction of the drug absorbed from the gastrointestinal tract and E_h is the hepatic extraction ratio. Given that the drug has 40% absorption (f_a = 0.4) and a hepatic extraction ratio (E_h) of 0.6, we can substitute these values into the formula: F = 0.4 * (1 - 0.6) = 0.4 * 0.4 = 0.16 or 16%. This matches option D, indicating that the bioavailability of the drug is 16%.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option does not match our calculated bioavailability of 16%, and without a specific value, we cannot directly assess its incorrectness, but we know it does not equal 16%.
- **Option B:** Similarly, this option does not correspond to the calculated bioavailability of 16%, and its value would be incorrect based on our calculations.
- **Option C:** This option also does not match the calculated value of 16% and thus is incorrect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that drugs with high first-pass metabolism have low bioavailability when administered orally. This is why some drugs, like propranolol and morphine, are often given parenterally or in modified-release formulations to optimize their bioavailability and therapeutic effect.

## **Correct Answer:** D. 16%