**Question:** Percentage of Halothane metabolized -

A. 25%
B. 50%
C. 75%
D. 100%

**Core Concept:** Halothane is a volatile anesthetic agent used for general anesthesia induction and maintenance. It is a halogenated ether compound with a relatively high potency and low toxicity. The primary pathway for halothane's elimination is by oxidation through the cytochrome P450 enzymes in the liver, specifically CYP2A6, CYP2B6, and CYP2E1.

**Why the Correct Answer is Right:** Halothane is primarily eliminated through the cytochrome P450 enzymes in the liver. The correct answer states that approximately 75% of halothane is oxidized and eliminated, leaving 25% unchanged in the circulation. This highlights the role of liver enzymes in halothane clearance and its contribution to anesthetic depth and recovery time.

**Why Each Wrong Option is Incorrect:**

A. 25% is incorrect because it does not accurately represent the overall percentage of halothane being eliminated.
B. 50% is incorrect because it does not align with the primary pathway of halothane elimination (75%) and does not consider the remaining 25% that remains unchanged in the circulation.
C. 75% is incorrect because the correct answer already states that 75% of halothane is eliminated, and the question asks for the percentage not eliminated.
D. 100% is incorrect because it is not relevant to the primary pathway of halothane elimination, which is oxidation through cytochrome P450 enzymes. Additionally, 100% would mean no halothane is present in the circulation, which is not the case in clinical practice.

**Clinical Pearl:** Understanding the primary pathway of halothane elimination is crucial for safe anesthetic practice. The liver enzymes (cytochrome P450 enzymes) play a significant role in anesthetic drug clearance, affecting anesthetic depth, recovery time, and patient safety.

**Correct Answer:** C. 75% Halothane is primarily eliminated through the cytochrome P450 enzymes in the liver, resulting in 75% of the administered dose being oxidized and eliminated. The remaining 25% remains unchanged in the circulation, contributing to the depth of anesthesia and recovery time.