WBR0442

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A researcher, assessing difference between the intravenous (IV) and the oral forms of metoprolol, administers 20 mg of the IV formulation of metoprolol to one group of mice and 40 mg of the PO formulation to another group. He then records the plasma concentrations every 5 minutes until the drug levels become undetectable. He records an AUC for the IV form of 97.8 mg.hr/L and an AUC of 65.3 mg.hr/L for the PO form. What is the bioavailability of the oral form of metoprolol?]]
Answer A	AnswerA::33.38%
Answer A Explanation	AnswerAExp::This is the absolute bioavailability of metoprolol based on this experiment.
Answer B	AnswerB::52.55%
Answer B Explanation	AnswerBExp::This is not the absolute bioavailability of metoprolol.
Answer C	AnswerC::66.77%
Answer C Explanation	AnswerCExp::This is not the absolute bioavailability of metoprolol.
Answer D	AnswerD::74.88%
Answer D Explanation	AnswerDExp::This is not the absolute bioavailability of metoprolol.
Answer E	AnswerE::89.90%
Answer E Explanation	AnswerEExp::This is not the absolute bioavailability of metoprolol.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Bioavailability is the proportion of a drug administered via any route that reaches the systemic circulation. In pharmacokinetic terms, bioavailability (F) is defined as the relative area under the plasma concentration-time curve (AUC) of a formulation compared to the IV formulation. In the IV form, all drugs have a bioavailability of 100% as all the drug administered immediately reaches the systemic circulation. The absolute bioavailability of the oral form of a drug can be calculated using the following equation: F = (AUCPO x DoseIV) / (AUCIV x DosePO). For any given formulation, determining the absolute bioavailability requires comparison to the IV form of the drug using the same equation. To determine relative bioavailability and compare 2 non-intravenous formulations, the following equation is used: F = (AUCA x DoseB) / (AUCB x DoseA). Educational Objective: The absolute bioavailability of the oral form of a drug can be calculated using the following equation: F = (AUCPO x DoseIV) / (AUCIV x DosePO). References: Katzung BG, Masters S, Trevor A. Basic and Clinical Pharmacology 12/E. McGraw Hill Professional; 2012.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Bioavailability, WBRKeyword::Pharmacokinetics, WBRKeyword::Oral, WBRKeyword::Intravenous, WBRKeyword::Equation, WBRKeyword::Formula, WBRKeyword::Calculation
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::