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). |
| 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:: |