A drug given at the loading dose of 20mg reaches plasma concentration of 0.5mg/L, If apparent volume of distribution is 40L, Calculate Bio availability of the drug
**Question:** A drug given at the loading dose of 20mg reaches plasma concentration of 0.5mg/L, If apparent volume of distribution is 40L, Calculate Bio availability of the drug
**Core Concept:** Bioavailability is defined as the fraction of an administered drug dose that reaches the systemic circulation, and is calculated as the ratio of actual drug exposure (AUC_t) to theoretical drug exposure (AUC_inf).
**Why the Correct Answer is Right:**
The correct answer is **D**. Bioavailability (F) can be calculated using the following formula:
F = (AUC_t / AUC_inf) * 100%
Given that the drug is administered as a loading dose of 20mg and reaches a plasma concentration of 0.5mg/L, we can calculate the actual drug exposure (AUC_t) and the theoretical drug exposure (AUC_inf).
**Why Each Wrong Option is Incorrect:**
Option A: Bioavailability cannot be determined directly with the given information. We need at least two doses or a constant infusion to calculate AUC_inf.
Option B: Bioavailability is not calculated using the plasma concentration and dose. It involves the ratio of AUC_t to AUC_inf.
Option C: Bioavailability is not calculated using the plasma concentration at steady state. Bioavailability is determined based on the ratio of AUC_t to AUC_inf.
**Why the Correct Answer is Right:**
The apparent volume of distribution (Vd) is given as 40L. Bioavailability can be calculated using the following formula:
F = (AUC_t / AUC_inf) * 100%
In this case, we can calculate AUC_inf, which is the ratio of the total drug exposure to the actual drug exposure (AUC_inf = AUC / (1/K_el)):
AUC_inf = (AUC_t / (1/K_el)) * 100%
**Core Concept Explanation:**
The apparent volume of distribution (Vd) represents the distribution of the drug among the compartments of the body. In this case, the apparent volume of distribution (Vd) is 40L.
**Core Concept Explanation:**
Bioavailability is a measure of the fraction of a drug dose that is absorbed into the systemic circulation. It is a crucial parameter in understanding the efficacy and safety of a drug.
**Why the Correct Answer is Right:**
The correct calculation of bioavailability requires the ratio of the actual drug exposure (AUC_t) to the theoretical drug exposure (AUC_inf), as well as the elimination rate constant (K_el). The formula for bioavailability is:
F = (AUC_t / (1/K_el)) * 100%
**Core Concept Explanation:**
K_el represents the rate at which the drug is eliminated from the body, while AUC_t represents the total area under the plasma concentration-time curve