A drug administered through which of the following routes undergo high first pass metabolism?
**Core Concept**
High first-pass metabolism refers to the extensive metabolism of a drug as it passes through the liver after oral administration. This phenomenon is particularly significant for drugs that are highly extracted by the liver, resulting in significant bioavailability reduction.
**Why the Correct Answer is Right**
The correct answer is the oral route, which involves the liver's extensive first-pass metabolism. When a drug is administered orally, it is absorbed into the bloodstream and then passes through the liver before reaching systemic circulation. The liver enzymes, particularly the cytochrome P450 system, play a crucial role in metabolizing the drug, often resulting in reduced bioavailability. This is why many orally administered drugs require high doses to achieve therapeutic effects.
**Why Each Wrong Option is Incorrect**
**Option A:** Inhalational route does not undergo significant first-pass metabolism, as the drug is absorbed directly into the bloodstream without passing through the liver.
**Option B:** Topical route also avoids significant first-pass metabolism, as the drug is applied directly to the skin or mucous membranes, minimizing systemic absorption.
**Option C:** Parenteral routes, such as intravenous or intramuscular administration, bypass the liver's first-pass effect, allowing the drug to reach systemic circulation more directly.
**Clinical Pearl / High-Yield Fact**
Drugs with high first-pass metabolism often require prodrugs, which are converted to active metabolites after passing through the liver. This can help increase bioavailability and reduce the required dose.
**Correct Answer:** C. Parenteral routes.