**Question:** From which of the following routes, bioavailability of the drug is likely to be 100 percent?

A. Intranasal
B. Intrathecal
C. Intravenous
D. Sublingual

**Core Concept:** Bioavailability (F) is a measure of how much of a drug reaches the systemic circulation when administered orally. It is calculated as a percentage and takes into account factors such as absorption, distribution, and first-pass effect. Bioavailability is usually less than 100% because of these factors.

**Why the Correct Answer is Right:** In this case, the correct answer is "Intravenous" (C) because when a drug is administered intravenously (IV), it bypasses the first-pass effect in the liver. The drug is directly introduced into the systemic circulation, ensuring that a significant amount reaches the target site without being broken down or neutralized first. As a result, bioavailability is likely to be close to 100%.

**Why Each Wrong Option is Incorrect:**

A. Intranasal (A) administration has a high absorption rate due to its direct contact with the mucosal lining of the nasal cavity. However, bioavailability is not guaranteed to be 100% because factors like pH, temperature, and enzymatic activity can affect absorption.

B. Intrathecal (B) administration is used for drugs administered to the spinal cord or cerebrospinal fluid, but it does not guarantee 100% bioavailability due to factors like incomplete distribution and potential drug degradation in the cerebrospinal fluid.

D. Sublingual (D) administration is commonly used for drugs like nitroglycerin to improve absorption. However, bioavailability is not guaranteed to be 100% because factors like pH, enzymatic activity, and slow absorption can affect the amount of drug that reaches the systemic circulation.

**Clinical Pearl:** In clinical practice, it is essential for healthcare professionals to understand bioavailability and its limitations to appropriately choose the most effective and safe route of drug administration for the patient's condition and drug characteristics.

**Correct Answer Explanation:** Bioavailability is crucial when determining the optimal route of drug administration, ensuring the most effective and safe treatment for the patient. Understanding the limitations of bioavailability helps healthcare professionals choose the most suitable route for administering medications based on the drug's properties and the patient's condition.