Drug Absorption (01/02/19) Flashcards
1
Q
What is rate of transport of diffusion across membrane dependent on?
A
- permeability
- surface area
- concentration difference
2
Q
What influences drug availability for absorption?
A
-Disintegration time
-Dissolution rate
Both above can be easily modified
- Gastric Emptying
- pH + viscosity
- Surface area
- Epithelial transport process
- Intestinal transit time
- Metabolism
- Blood flow
3
Q
Advantage of Buccal and sublingual admin?
A
-permeability better than skin but not as good as intestine
- convenient
- fast
- avoids first pass metabolism
4
Q
Characteristics of stomach
A
- low surface area (epithelial layer is smooth compared to intestines)
- tight junctions
- no nutrient transporters (therefore very little absorption) EXCEPT: drugs with high permeability like ethanol, and weak acids like aspirin
5
Q
Characteristics of Small intestine
A
- large surface area
- extensive blood supply
- nutrient transport
- first pass metabolism
- transit time 3-4 hours
6
Q
What is Splanchnic circulation?
A
- intestinal veins flow into portal vein of liver
- blood rich in absorbed material is filtered
-All drugs from intestinal epithelium filters through liver before dilution, and distribution to whole body
7
Q
What are the types of pathways for absorption?
A
- Transcellular (through epithelia) (mainly lipophilic move via this route)
- Paracellular (between epithelial cells) (mainly hydrophilic molecules)
- Carrier mediated (requires transporter) (mainly hydrophilic)
- Transcytosis (does not involve transporter, but vesicles engulf and spit out drug on other side) (mainly for hydrophilic)
8
Q
Which drugs will pass lipid bilayer through epithelial cells?
A
- lipophilic drugs
- drugs obeying Lipinski’s rules (small, lipophilic, LogP>0)
- UN-ionised
9
Q
Which drugs pass through gaps between cells (paracellular)?
A
- drugs with low MW and log P<0
