Biopharmaceutics Flashcards
What is a drug?
An active pharmaceutical ingredient
What is a medicine?
The dosage form
What does biopharmaceutics refer to?
How a dosage form interacts with physiological systems
When would a SDF have 0 bioavailability?
If it fails to disintegrate and pass through the body intact - none of it enters systemic circulation
OR
if it disintegrates in the stomach and is broken down by acid hydrolysis - doesn’t enter systemic circulation
What kind of drug would have 100% bioavailability?
A drug that is injected intravenously - it enters systemic circulation
What is absolute bioavailability?
The fraction of drug in the dosage form that reaches systemic circulation
Why is absolute bioavailability used as a measure?
- Blood can easily be sampled
- Blood is the central compartment from which drugs are distributed
- Absorption occurs when a drug enters the central compartment
- Formulation is only relevant to absorption
Which routes of administration bypass the epithelial layer?
- Intravascular : i/v or i/a
2. extravascular : s/c, i/m or i/p
Which routes of administration go across the epithelial layer?
- Skin
- Small intestine
- Buccal, gastric, rectal
- Nasal, bronchial, pulmonary
Where does absorption occur in transdermal dosage forms?
In the capillary bed of the dermis
What do the stratum corneum and epidermis do for the skin?
Provide a waterproof barrier - prevents entry of substances into the skin
What is the stratum corneum made of?
Dead cells
What is the epidermis made of?
Tightly packed dead cells
Which physiological factors influence drug absorption?
- Rate of transit
- Properties of lumen fluid
- Tissue properties at site of absorption
What are the advantages of buccal administration?
- Convenient
- Fast
- Avoids 1st pass metabolism by liver
What does gastric emptying depend on?
Whether someone has eaten or nah
Residence time in stomach increases when you have eaten
How is the mouth adapted for absorption?
Has a low SA but has greater permeability than the skin
How is the stomach adapted for absorption?
Low SA with tight junctions and no transporters for nutrient absorption therefore little absorption occurs (except for high permeability or weak acid drugs)
How is the small intestine adapted for absorption?
Very large surface area due to folds, villi and microvilli.
Large blood supply, nutrient transporters and paracellular transporters.
What is the typical transit time through the small intestine?
~3-4 hours
Which drugs are are suitable for transcellular absorption?
Small lipophilic drugs
Which drugs are suitable for paracellular absorption?
Drugs with low molecular weight but LogP <0
