Question

a nurse is caring for a client who is receiving nitroglycerin iv and is switching to the oral form of the medication. the nurse should identify that the oral dose will be higher than the iv dose for which of the following reasons?

• the iv form crosses the blood-brain barrier.
• the oral form has a decreased half-life.
• the oral form has decreased bioavailability because of the first-pass effect.
• the oral form has an increased rate of excretion.

Explanation:

To determine the correct answer, we analyze each option:

• The first option is incorrect because the ability to cross the blood - brain barrier is not related to the difference in doses between IV and oral nitroglycerin.
• The second option is wrong. Oral nitroglycerin does not have a decreased half - life compared to IV nitroglycerin in a way that would explain the dose difference.
• The third option is correct. The first - pass effect occurs when a drug is absorbed from the gastrointestinal tract and then metabolized by the liver before reaching the systemic circulation. This reduces the bioavailability of the oral form. So, to achieve the same therapeutic effect as the IV form (which bypasses the first - pass effect and has 100% bioavailability), a higher oral dose is needed.
• The fourth option is incorrect. An increased rate of excretion would not explain the need for a higher oral dose; in fact, it would likely require more frequent dosing rather than a higher single dose.

Answer:

The oral form has decreased bioavailability because of the first - pass effect.