Review Question - QID 106854

The calculated absolute bioavailability of compound X is 67%. Absolute bioavailability (F) = (AUC-oral * Dose-IV)/(AUC-IV * Dose-oral), where AUC is the area under the curve of a pharmacokinetic plot of the drug's plasma concentration versus time for each drug formulation.

Bioavailability is the proportion of an administered dose of a medication that reaches the systemic circulation. IV administration yields a bioavailability of approximately 100%. Other routes, such as oral, rectal, intramuscular, have a lower bioavailability due to incomplete absorption, first-pass metabolism in the liver, or distribution of the agent into other tissues.

Oliphant et al. review the pharmacokinetics of quinolone antibiotics. Oral quinolone agents have excellent bioavailability, with roughly equal serum drug concentrations when the antibiotic is given either intravenously or orally. This high oral bioavailability allows for early transition of patients from IV to oral antibiotics.

Morrow et al. compare the bioavailability of IV methylprednisolone versus oral prednisone in multiple sclerosis patients. 24 hours after administration of either 1250 mg of oral prednisone or 1 g of IV methylprednisolone, the measured AUC for the 2 agents was not significantly different, with a p value of 0.122.

Illustration A summarizes the calculations to arrive at the answer in the question above. Illustration B shows the plasma concentration versus time graph upon which the area under the curve (AUC) is calculated for the determination of bioavailability.

Incorrect Answers:
Answers 1,2,4,5: Given the information in the question stem and the equation listed above, the calculated bioavailability of Compound X is 67%.