Exam 2 - Oral Bioavailability Flashcards
F (oral bioavailability)
the fraction of the dose that reaches the systemic administration intact following an oral dose
F range
0 to 1
Factors affecting F
- f(d): fraction dissolved
- f(gl): fraction not degraded in the gut lumen
- f(a): fraction absorbed
- f(gw): fraction not degraded in the gut wall
- f(h): fraction not degraded in the liver
Which types of drugs have low oral bioavailability? (4)
- High E drugs
- Aminoglycosides
- Peptides & Proteins
- Newer small molecule drugs
Why do high E drugs have low oral bioavailability?
Hepatic first pass metabolism - low f(h)
Why do aminoglycosides have low oral bioavailability?
They are poorly absorbed - low f(a)
Why do peptides & proteins have low oral bioavailability?
They are degraded in the gut lumen - low f(gl)
Why do newer small molecule drugs have low oral bioavailability?
They have low solubility - low f(d)
Absolute bioavailability
F in reference to an IV dose
Relative bioavailability
F in refence to another extravascular dose
What is one use for relative bioavailability?
To compare generic tablets to the brand(innovator)
Biopharmaceutics Classification System (BCS)
Indentifies drugs likely to have low F using in vitro tests
BCS Class 1
- High solubility
- High permeability
- Rapid dissolution
BCS Class 2
- Low solubility
- High permeability
BCS Class 3
- High solubility
- Low permeability
