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What is percutaneous absorption?
Absorption of substances from outside of the skin to underneith the skin and into the blood stream
What are the factors influencing percutaneous absorption?
- Physical and chemical properties
- Pharmaceutical vehicle
- Condition of the skin
What is the major rate limiting barrier to transdermal drug transport?
Stratum Corneum (Horny Layer)
WHat is the stratum corneum?
The outer layer of the skin that is composed of partially desiccated non-living cells + film (sebum and sweat) and karatin.
What layer of the skin is not significant in drug penetration?
The stratum corneum
What is the layer of skin where the barrier layer with living cells at several differentiated levels?
What is the living epithelium?
What is the layer of skin that is the living epidermis?
What is the layer of skin that has basal layers separating from dermis?
What is the layer of skin that has vascularized tissue that drug must reach?
What is transcellular?
Non-polar drugs that tend to cross cell barrier through lipid rich regions
What is intracellular?
- Medication that can diffuse through the space between cells
- Channels are the major route of drug penetration
- Polar drugs
What is trans-appendageal ?
- Accross the skin appendages
- hair follicles
- Sweat Glands
- Sebaceous glands
- Minor drug absorption
What are the factors relating the drug that affect absorption through the skin?
- Concentration of drug
- Particle size
- Molecular weight
- Solubility in both oil and water
- Attraction to skin
What the factors relating to the vehicle that affect absorption through the skin?
- Adherence to skin
- Miscibility with sebum
- Action as a moisture barrier (hydration of skin)
What are the factors relating to the skin that affect absorption through the skin?
- Intact or broken skin
- Surface area applied
- Site of application (thin horny)
What are the factors relating to the physical factors that affect absorption through the skin?
- Rubbing (inunction)
- Exercise = vasodilation
- Time of contact with skin
- Mutiple applications (saturation)
What are the chemical methods of enhancing percutaneous absorption?
- Reduction of S. Corneum resistance
- Modification of S. Corneum hydration
- Modification of lipids in intracellular channels
- through carrier mechanism
What are the solvent, chemical percutaneous enhancers?
- Alkyl methyl sulfoxides
- Micellaneous: acetone, dimethyl acetamide, dimethyl formamide
What are the amphiphies, chemical enhancers?
- Anionic surfactant
- Cationic surfactant
- Amphoteric surfactant
- Nonionic surfactant
- Fatty Acid and alcohol
What are examples of anionic surfactant?
What are examples cationic surfactant?
Quaternary ammonium salts, preservative
What are examples of amphoteric surfactant?
- Alkyl betamines
What are examples of nonionic surfactant?
Mon, di and triglycerides
What are examples of fatty acids and alcohol for chemical percutaneous enhancer?
- Stearyl Alcohol
What are the physical methods of enhancers?
What is ionophoresis?
Delivers a charged chemicals across the skin using eletrical field
What is sonophoresis?
High-frequency ultrasound facilitates drug penetration through S. Corneum
What are rate controlling systems intended to do?
- The drug is release promptly from the system into the S. Corneum for penetration into general circulation
- Systemic Affect
- Cause occlusion of the skin so there is only one way flux of drug, which is a therapuetic advantage over other dosage forms (nothing is loss)
- Design must avoid proliferation of bacteria under occluded skin
- Cause no irritation or sensitization to the skin due to drug, vehicle or adhesive
- Deliver drug at a controlled rate to intact skin without building up in the dermis layer
- Skin is not the targe
- Increase patient compliance
What are the advantages of TDDS?
- Avoid the GI
- Substitute for oral administration, and parental
- Avoid first pass effect
- Provide mult-day therapy with single patch
- Drug effect terminated when the patch is taking off
- Fast identification of patch during emergencies
What are the disadvantages of TDDS?
- Can be put on irritating skin
- Only can use potent drugs
- Technical difficulties