The nitrate which does not undergo first-pass metabolism is:
**Core Concept**
Nitrate medications, used primarily for angina pectoris, undergo first-pass metabolism in the liver, which reduces their efficacy. This concept is crucial in understanding the pharmacokinetics of nitrates and their clinical applications.
**Why the Correct Answer is Right**
Isosorbide dinitrate (ISDN) is a nitrate that does not undergo significant first-pass metabolism. This is because it is absorbed directly into the bloodstream from the gastrointestinal tract, bypassing the liver. As a result, ISDN maintains its potency and efficacy, making it a preferred nitrate for the treatment of angina. The lack of first-pass metabolism also contributes to the drug's rapid onset of action.
**Why Each Wrong Option is Incorrect**
**Option A:** Isosorbide mononitrate (ISMN) is another nitrate that undergoes metabolic degradation, but it is not the correct answer since it is a metabolite of ISDN and still undergoes first-pass metabolism to some extent.
**Option B:** Glyceryl trinitrate (GTN) is a nitrate that undergoes significant first-pass metabolism, which reduces its efficacy. It is often administered sublingually or transdermally to bypass the liver.
**Option C:** Pentaerythritol tetranitrate (PETN) is another nitrate that undergoes first-pass metabolism, although its exact metabolic pathway is less well-characterized.
**Clinical Pearl / High-Yield Fact**
When choosing a nitrate for the treatment of angina, it is essential to consider the pharmacokinetic properties, including the degree of first-pass metabolism. Isosorbide dinitrate's ability to bypass first-pass metabolism makes it a preferred choice for patients with angina.
**Correct Answer:** C.