transdermal pharmaceutic workshop

Question 1

how do painless and needle free injections work?

Answer 1

1. spring powered
2. high pressure gas to force drug through the skin
   both are resoluble and needle free

Question 2

how do micro needle patches work?

Answer 2

• increase skin permeability by creating micron scale pathways through the skin
• actively drive drug through the skin
  targets the SC although can also pass to epidermis
  (either drug coated or dissolving micro needles encapsulating drug)

Question 3

whats the most common route of permeation for lipophilic (has to be) transdermal drugs?

Answer 3

intercellular route

Question 4

whats the best TDD patch profile?

Answer 4

5-25mg
6-8hrs half life
less than 200 degrees mpt
logP between 1 and 3
MW less than 1000 but ideally less than 500
50cm2 max patch size
no or few polar centres like carboxylate/zwitterionic structures

Question 5

how does increasing chemical potential increase permeation of the drug?

Answer 5

max penetration is when drug is at highest thermodynamic activity,
so we do this by making it a supersaturated solution (by evaporation of solvent or mixing of co-solvents)
when water removed from skin and acts as an anti-solvent, flux increases by 5-10x
these SS systems are unstable so require anti-nucleating systems
but fatty acids, cholesterol in the SC already have an anti-nucleating effect

Question 6

how do eutectic systems work to increase permeability of the drug?

Answer 6

reduces the overall mpt to skin temp, by inhibiting the crystalline process of 2 components

Question 7

give an example of drug that uses a eutectic system

Answer 7

EMLA cream

mixture of lignocaine and prilocaine

Question 8

certain eutectic systems interact with the SC swell as reducing the mat of the drug, give an example?

Answer 8

some have a penetration enhancer ad their second component e.g. ibuprofen with terpenes

Question 9

what is the ER?

Answer 9

enhancement ratio: permeation after treatment/permeation before treatment

Question 10

how does hydration of the SC improve skin permeation?

Answer 10

addition of water makes the skin swell and expand, opening up the SC so it becomes more aqueous and so increased penetration

Question 11

water in oil … water whereas oil in water … water

Answer 11

prevent

donate

Question 12

how do liposomes improve skin permeation

Answer 12

lipids similar to lipids of SC fuse together so these liposomes act to fluidise the lipids of the SC

Question 13

what are the types of liposomes

Answer 13

deformable: surfactants make them mouldable and able to squeeze through channels in the SC
ethosomes: ethanol to fluidise the lipids
niosomes: non-ionic surfactants
solid lipid nanoparticles: carriers for delivery of sunscreen and vitamins

Question 14

how can we disrupt the layers of the SC?

Answer 14

1. add urea and surfactants
2. or fluidise the lipids by adding DMSO, alcohols and fatty acids
   either mix these in or extract the lipids (forming aq channels), or at high conc, pool the lipid to create permeable pores

Question 15

solubility parameters?…

Answer 15

you want your solubility parameter of the drug to be similar to that of the SC to reduce irritation of the skin and improve solubility
- can be changed by adding ethanol, polyethylene glycol (co-solvents)