Topical drug delivery Flashcards
How thick is the stratum corneum?
0.01mm
How thick is the epidermis?
0.1mm
How thick is the dermis?
1.0mm
What are the ‘bricks’ and ‘mortar’ of the stratum corneum?
Bricks=dead keratin filled cells
Mortar=complex lipid mixture
What are the ‘rivets’ holding corneocytes together called?
corneodesmosomes
On average how thick is the skin?
1mm
What percentage of an adults weight is water?
60%
How much water do we lose across the skin per day?
200-300mL
When the drug penetrates the skin, what is it then taken up by?
Microcirulation
Name 5 ways of assessing the skin bioavailability in vivo in man
Tape stripping Suction blister Microdialysis Biopsy Blood levels
In general, maximum flux across the skin decreases with increasing what?
Molecular weight
Maximum flux increases with what up to a point?
Lipophilicity
After the stratum corneum, the drug must cross what to reach micocirculation?
Viable dermis and upper dermis
What is the rate determining barrier of the skin?
Stratum corneum
What is the skin surface pH?
4-5.5
Are ionised or unionised drugs best absorbed across the skin?
Unionised
Are skin formulations usually high low or neutral pHs?
Neutral
What is the lag time?
Time required to establish linear concentration gradient
Transdermal delivery has what kind of kinetics?
Flip-flop
Describe the kinetics when a drug is given orally?
Kinetics of absorption are faster than kinetics of elimination
Described the kinetics when a drug is given topically
Kinetics of absorption are usually slower than kinetics of elimination. Flip-flop kinetics
MEC?
Minimum effective concentration
MTC?
Minimum toxic concentration
What are the disadvantages to GTN ointment?
Larger dose, slower onset of action
What are the advantages to GTN ointment?
skin ‘control’, sustained effect
