What is absorption?
Movement of drug into the blood stream
What effects absorption (2)
1.Route of administration
2. Permeation - how many barriers to cross
Give 4 features of oral administration
- Convenient
- Efficient
- Uses pH differences in gut
- Subject to first pass metabolism
Give 3 features of buccal administration
- Uses high blood flow
- Avoids first pass metabolism
- Works quickly
Give 2 benefits of rectal administration
- Avoids first pass metabolism
- Non consistent absorption
Benefits of inhalation (2)
- Large surface area
- High blood flow
Used volatile anaesthetics and asthma
Benefits of topical (2)
- Local effects
- Low systemic effects but not none
Transdermal - what to consider? (3)
- Relies on lipid permeation
- May cause irritation- bringing blood to surface
- Don’t cut
I/V vs I/M
- IV quicker no absorption barrier
2.IV 100% bioavailability
3.IM depends on blood flow and perfusion of muscles
What is bioavailability
Amount of drug that gets into circulation
- area under graph
- slope indicates administration
Does bioavailability indicate effectiveness?
No
What is bio equivalence ?
Therapeutic equivalency of 2 drugs ie generics
Some inequivalent so must prescribe brand eg lithium
What effects absorption? (7)
- Formulation
- Dissolution of particles
- Chem stability eg pH / enzymes
- Gut motility
- Food in gut
- Passage across GI tract walls
- Blood flow to GI tract
What is drug half life t1/2
Time for concentration of drug in blood to fall by half
How many half lives to get to steady state ?
5
How can we speed up time to get to steady state?
Give loading dose
What are the 4 main mechanics of drug permeation
- Aqueous diffusion
- Lipid diffusion ( most important- cell membrane has lipids)
- Facilitated diffusion- carrier mol needs energy ATP
- Pinocytosis - cell envelopes drug - bulky molecules eg proteins or hormones
What does permeation depend on? ( 3)
- Size of mol
- Surface area
- Concentration gradient
