What is a key consequence of bypassing the absorption phase in IV administration?

What is a key consequence of bypassing the absorption phase in IV administration?

• A. There is greater variability in exposure
• B. Gastric emptying determines onset
• C. You know exactly how much drug is in the blood
• D. First-pass metabolism increases bioavailability

Answer: (C)

When a drug is given IV, it goes straight into the bloodstream, so systemic bioavailability is essentially 100%. That means the amount of drug entering circulation is the entire administered dose, at least at the moment of injection. Because there’s no absorption step to limit or fluctuate how much drug gets into the blood, you have a predictable starting amount in the bloodstream, which is the basis for calculating initial plasma concentrations from the dose and the volume of distribution. In contrast, the other statements don’t fit this scenario. There’s no absorption phase to be governed by gastric emptying, so gastric emptying doesn’t determine onset for IV dosing. First-pass metabolism is bypassed with IV administration, so it doesn’t increase bioavailability; it’s the route that avoids the first-pass effect altogether. And variability in exposure due to absorption is minimized (not increased) because absorption is not involved. So the key consequence is that you know exactly how much drug is in the blood, since the full dose reaches systemic circulation.

When a drug is given IV, it goes straight into the bloodstream, so systemic bioavailability is essentially 100%. That means the amount of drug entering circulation is the entire administered dose, at least at the moment of injection. Because there’s no absorption step to limit or fluctuate how much drug gets into the blood, you have a predictable starting amount in the bloodstream, which is the basis for calculating initial plasma concentrations from the dose and the volume of distribution.

In contrast, the other statements don’t fit this scenario. There’s no absorption phase to be governed by gastric emptying, so gastric emptying doesn’t determine onset for IV dosing. First-pass metabolism is bypassed with IV administration, so it doesn’t increase bioavailability; it’s the route that avoids the first-pass effect altogether. And variability in exposure due to absorption is minimized (not increased) because absorption is not involved.

So the key consequence is that you know exactly how much drug is in the blood, since the full dose reaches systemic circulation.