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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}} {{Alison}}
|QuestionAuthor={{SSK}} {{Alison}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pharmacology
|MainCategory=Pharmacology
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|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|SubCategory=Cardiology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
|MainCategory=Pharmacology
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|MainCategory=Pharmacology
|MainCategory=Pharmacology
|SubCategory=Cardiology
|SubCategory=Cardiology
|Prompt=A researcher, assessing difference between the intravenous (i.v.) and the oral forms of metoprolol using mice, administers both drugs to the mice and notes the following plasma concentrations of the medications illustrated in the graph below. Which of the following equations best corresponds to the bioavailability (F) of metoprolol in the oral form?
|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?
 
[[Image:WBR Bioavailability.png]]
|Explanation=[[Bioavailability]] (F) is defined as the proportion of the total area under the plasma concentration-time curve (AUC).  The relative [[bioavailability]] of the oral form of a drug can be calculated using the following equation: F = (AUCoral / AUCi.v.) x (Dosei.v./Doseoral)
 
|EducationalObjectives=
Bioavailability can be calculated with the following equation: F = (AUCoral / AUCi.v.) x (Dosei.v./Doseoral)
|References= First Aid 2014 page 239


|AnswerA=F = (AUCoral / AUCi.v.) x (Dosei.v./Doseoral)
|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 = (AUC<sub>PO</sub> x Dose<sub>IV</sub>) / (AUC<sub>IV</sub> x Dose<sub>PO</sub>). 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 = (AUC<sub>A</sub> x Dose<sub>B</sub>) / (AUC<sub>B</sub> x Dose<sub>A</sub>).
|AnswerAExp=Bioavailability can be calculated using the equation: F = (AUCoral / AUCi.v.) x (Dosei.v./Doseoral)
|AnswerA=33.38%
|AnswerB=(AUCoral / Doseoral ) x (AUCi.v. x  Dosei.v.)
|AnswerAExp=This is the absolute bioavailability of metoprolol based on this experiment.
|AnswerBExp=This equation is not used to calculate bioavailability.
|AnswerB=52.55%
|AnswerC=(AUCi.v. / AUCoral) x (Doseoral x Dosei.v.)
|AnswerBExp=This is not the absolute bioavailability of metoprolol.
|AnswerCExp=This equation is not used to calculate bioavailability.
|AnswerC=66.77%
|AnswerD=(Doseoral x AUCoral) x (Dosei.v. x AUCi.v.)
|AnswerCExp=This is not the absolute bioavailability of metoprolol.
|AnswerDExp=This equation is not used to calculate bioavailability.
|AnswerD=74.88%
|AnswerE=(AUCoral + Doseoral) / (AUCi.v. + Dosei.v.)
|AnswerDExp=This is not the absolute bioavailability of metoprolol.
|AnswerEExp=This equation is not used to calculate bioavailability.
|AnswerE=89.90%
|AnswerEExp=This is not the absolute bioavailability of metoprolol.
|EducationalObjectives=The absolute [[bioavailability]] of the oral form of a drug can be calculated using the following equation: F = (AUC<sub>PO</sub> x Dose<sub>IV</sub>) / (AUC<sub>IV</sub> x Dose<sub>PO</sub>).
|References=Katzung BG, Masters S, Trevor A. Basic and Clinical Pharmacology 12/E. McGraw Hill Professional; 2012.
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Bioavailability, pharmacokinetics, pharmacodynamics, oral, intravenous, equation, formula, calculation
|WBRKeyword=Bioavailability, Pharmacokinetics, Oral, Intravenous, Equation, Formula, Calculation
|Approved=Yes
|Approved=Yes
}}
}}

Revision as of 19:02, 3 November 2014
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
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