[3] Bioavailability Flashcards
Formula for amount of drug absorbed reaching the plasma
F x Dose
Example:
F of Digoxin is 0.7
For Digoxin 250 ug preparation
How much is absorbed in oral?
How much is absorbed through IV?
Oral: 0.7 * 250 = 175 ug
IV: 250 ug
Definition: Area Under the Blood Concentration Curve (AUC)
Common measure of the extent of Bioavailability
Absolute Bioavailability is equal to?
F, the fraction of the dose that is Bioavailable
For drugs given intravascularly, what is F?
F = 1
Drug is completely absorbed
Formula: Absolute Bioavailability
[(AUC) PO / Dose PO] / [(AUC) IV / Dose IV]
Define: Relative Bioavailability
Bioavailability of a drug as compared to a recognized standard
Formula: Relative Bioavailability
(AUC) A / (AUC) B
Where drug product B is the recognized reference standard
[Question]
Oral F is 50%
Standard IV Dose is 50 mg
What should the ORAL dose be if the goal is to reach the same plasma drug concentration?
100mg
Define: First Pass Effect
Decreases the amount of active drug reaching the systemic circulation
Why is Lidocaine given intravenously?
Extensive first pass effect so oral doses would be extremely large
Rate of Absorption is measured by?
Tmax
What is considered one of the most successful pieces of legislation ever passed?
Hatch-Waxman Amendments to FFD&C Act of 1984
Is bioequivalence the same as therapeutic equivalent?
They are EXPECTED to be
Why is only Cmax and AUC the really important to determine Bioequivalence?
Assuming these are similar, there is no reason that other factors (Vd, C, etc.) should be any different
How similar must the Cmax and AUC be of different drugs to be considered Bioequivalent?
90% CI must fit between 80-125%
[T/F] Given a graph of two drugs that look like they have the same CMax and AUC can you say they are Bioequivalent?
Cannot do it by eyeballing, must calculate
If a drug is not bioequivalent, is it a bad drug?
Not necessarily, it just cannot be said to be the generic version of the drug it is copying
[T/F] Bioequivalent drugs are always good drugs
F
It depends on the quality and other factors involved in the making of the drug
