Question 54

First-pass metabolism occurs with the oral route.

First-pass metabolism primarily occurs when a drug is administered orally. This process involves the drug being absorbed through the gastrointestinal tract and then metabolized in the liver before it enters systemic circulation, significantly impacting its bioavailability.

A) Subcutaneous

Subcutaneous administration involves injecting a drug into the fatty tissue beneath the skin, allowing it to enter the bloodstream directly without significant first-pass metabolism. Therefore, this option is incorrect regarding first-pass metabolism.

B) Oral

Oral administration is the correct answer as it involves the absorption of the drug through the digestive system, leading to metabolism in the liver before reaching the bloodstream. This is the hallmark of first-pass metabolism, as the liver processes the drug, reducing its concentration prior to systemic circulation.

C) Intramuscular

Intramuscular administration involves injecting a drug directly into muscle tissue, where it is absorbed into the bloodstream. This route does not undergo significant first-pass metabolism, making this option incorrect in the context of the question.

D) Intravenous

Intravenous administration delivers a drug directly into the bloodstream, bypassing the gastrointestinal tract and liver initially. As a result, this route does not experience first-pass metabolism, rendering this option incorrect.

Conclusion

First-pass metabolism is a crucial concept that specifically applies to the oral route of drug administration due to the drug's passage through the liver. The other routes—subcutaneous, intramuscular, and intravenous—do not involve this metabolic process, making them incorrect in this context. Thus, oral administration is definitively the correct answer.