Transdermal Flashcards
1
Q
What was the first Transdermal drug on the market?
A
TransdermalScop - Scopolamine used for motion sickness, nausea and vomiting (1979)
2
Q
What are the advantages of using Transdermal delivery?
A
- Avoids the 1st pass metabolism (skin metabolism )
- Avoids pain associated with injection
- Provides continuous ‘sustained release’ of drug without frequent dosing
- Self administration
- Non invasive
- Improves patient compliance
- Reduces side effects
- Allows removal of drug source
- Patient preferred
3
Q
What are the limitations to transdermal drug delivery?
A
- Only potent drugs can be used
- There is a lag time before effect is felt (not immediate). Not good for acute conditions
- Tolerance is developed
- Poor diffusion of large molecular weighted drugs
- Causes allergic and Irritant reactions
4
Q
Define Sustained release
A
Slow release of drug over an extended period of time
5
Q
What are the transdermal drug absorption routes?
A
- Transcellular route (water soluble drugs) - through the SC and corneocytes
- Intercellular route (Lipid soluble drugs) - endogenous lipid within the SC
- Trans-follicular route
6
Q
When selecting a drug for transdermal delivery what criteria must be satisfied?
A
- The partition coefficient of the drug must be between 1 -4. This means it has both water and lipid solubility
- Its molecular weight must be less than 500Da
- The drug must have a suitable solubility in water at pH 6 -7.4
- Drug must be potent - low dosage administration
7
Q
Transdermal formulation principles…
A
- Select a suitable drug
- low mw
- high potency
- log p 1 - 4
- The release of the drug
- appropriate release (sustained release)
- lipophilic drug in a hydrophobic base to enable release
- Vehicle should not retain drug
- Thermodynamics
- Concentration gradient
- Alcohol
- Good solvent but evaporates from skin
- Occlusion
- covering skin with impermeable membrane
