Calculate the loading dose of a drug whose systemic bioavailability will be 20%, Vd-200L and target concentration is 5gm/L
**Core Concept**
The loading dose of a drug is calculated to achieve a desired target concentration in the bloodstream, taking into account the drug's systemic bioavailability, volume of distribution (Vd), and the desired concentration. The formula for calculating the loading dose is: Loading Dose = (Desired Concentration x Vd) / Bioavailability.
**Why the Correct Answer is Right**
To calculate the loading dose, we need to rearrange the formula: Loading Dose = (Desired Concentration x Vd) / Bioavailability. Given that the desired concentration is 5 g/L, Vd is 200 L, and bioavailability is 20% (or 0.2), we can plug in the values to get: Loading Dose = (5 g/L x 200 L) / 0.2 = 5000 g. Since the bioavailability is 20%, the actual dose required to achieve the target concentration would be 5000 g / 0.2 = 25000 g. However, we are asked to calculate the loading dose, which is the dose required to achieve the target concentration in the blood, not the actual dose required to achieve the target concentration in the body. Therefore, the loading dose is 5000 g.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the volume of distribution (Vd) in the calculation.
**Option B:** This option is incorrect because it uses the bioavailability value in the numerator instead of the denominator.
**Option C:** This option is incorrect because it uses the desired concentration in the denominator instead of the numerator.
**Option D:** This option is incorrect because it does not provide a clear calculation for the loading dose.
**Clinical Pearl / High-Yield Fact**
When calculating the loading dose, it's essential to remember that the desired concentration and Vd are used in the numerator, while the bioavailability is used in the denominator. This can be remembered using the mnemonic "Numerator Nice Guys (Desired Concentration and Vd) / Denominator Dudes (Bioavailability)".
**Correct Answer: C. 5000 g.**