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What are some factors that influence percutaneous absorption?
- Physical and chemical properties of drugs
- Pharmaceutical vehicle
- Condition of the skin
What is percutaneous absorption?
Absorption of substances from outside the skin to underneath the skin, including enterance into the blood stream
What are the layers of the skin from outer to inner most?
- Epidermis: Stratum Corneum, Stratum Lucidum, Stratum Germinativum
What is another name for the stratum conreum?
- Horny layer.
- This is where Keratin is contained
The stratum lucidum is also called?
Describe the stratum corneum?
- Outer layer composed of partially desiccated nonliving cells and film (sevum and sweat) and keratin
- 15-25 layers of cells over most of the body
- Lacks continuity; not significant factor in drug penetration
- Behaves as a semipermeable artificial membrane to drug penetration by passive diffusion
- Major rate-limieting barrier to transdermal drug transport
Are there several layers of epithelia cells?
Yes and they are at different stages of differentiation
The skin is covered by an emulsified film of sebum, sweat, and dead celss that are constantl desquamating (peeling)
Describe the statum lucidium
- aka Stratum Granulosum
- Barrier layer with living cells at several differentiated levels
- Living epidermis
Describe the Statum Germinativum
- Living epidermis
- Has basal layer separating from dermis
Describe the dermis
Vascularized tissue that drug must reach
What is transdermal absorption?
From skin into circulation
- Lipid-rich, non-polar drugs
- Channels are the major route of drug penetration; polar drugs
- Across skin appendages
- Hair follicles, sweat glands, sebaceous glands, minor drug absorption
What are factors affecting absoprtion through the skin related to the drug?
Concentration of drug, particle size, molecular weight (100-800), solubility in oil and water, attraction to skin
What are factors affecting absorption through the skin related to the vehicle?
- Adherence to skin
- miscibility with sebum
- action as a moisture barrier (hydration of skin)
What are the factors affecting absoption through the skin related to the skin?
- Intact vs broken skin
- surface area applied
- site of application (thin horny layer)
What are the factors affecting absorption through the skin related to the physical factors?
- Rubbing (inunction or exercise lead to vasodilation
- Time of contact with skin
- Multiple application (Saturation)
Percutaneous absorption can be enhanced through what two methods?
Chemical methods work by?
- Reduction of Stratum Corneum's resistance
- Modification of Stratum Corneum's hydration
- Modification of lipids in intercellular channels
- Through carrier mechanisms
What solvents are exmaples of chemical percutaneous enhancers?
- Alcohols (methanol, ethanol, 2-propanol)
- Alkyl methyl sulfoxides (DMSO, decyl methyl sulfoxide, others)
- Pyrrolidones (2-pyrrolidone, n-methyl-2-pyrrolidone, others)
- Laurocapram (Azone)
- Miscellaneous (acetone, dimethyl acetamide, dimethyl formamide, etc)
What are amphiphiles?
- Both sides, polar and nonpolar
- Anionic surfactants
- Cationic surfactants
- Amphoteric suractants
- Nonionic surfactants
- Fatty acids and alchols
What are some examples of anionic surfactants?
What are some examples of cationic surfactants?
- Quaternary ammonium salts
- Also preservative
What are examples of amphoteric surfactants?
- Alkyl bentamines
What are examples of nonionic surfactants?
mono, di and triglycerides
What are some examples of alchols and fatty acids?
- stearyl alcohols
What are some physcial methods that enhance percutaneous absorption?
delivery of charge chemicals across the skin using electrical field
High-frequency ultrasound facilitates drug penetration through the Stratum Corneum
What are some advantages of TDDS?
- Avoid GI difficulties
- Substitute ORAL administration
- Avoid first-pass effect
- Substitute parenteral therapy
- Provide multi-day therapy with single application because they act as a reservoir of drug (better compliance)
- Drug effects can be terminated by removal of system
- Fast identification during emergencies
What are some disadvantages of TDDS?
- Unsuitable for irritating and sensitizing drugs or highly sensitive persons, contact dermatitis
- Only relatively potent drugs can be prepared as TDDS
- Technical difficulties during preparations of TDDS
What are the two different designs of TDDS?
- Monolithic system
- Membrane-controlled system
What is the monolithic system?
- Most have excess drug, continual drug avaliabilty
- The skin controls the rate of absorption of drug
- Maintains wide range of plasma concentration over which the drug is effective but not toxic
- Drug and molymer matrix (mixture) are blended or dissolved
- Drug-matrix layer is dried, gelled matrix (sheet or cylindrical form)
- Assembling between backing and frontal layers (foil cover-strip)
What is the membrane-controlled system?
- The system controls the rate of drug delivery, rate -controlling membrane
- Delivers uniform quantities of drug to the skin over a period of time
- Drug in the reservoir (liquid or gell) remains saturated and the release rate of drug is constant
- Adhesive layer contains an initial priming dose
- Backing layer (water resistant) and drug reservior (liquid or gel) and Controlling semipermeable membrane and adhesive layer containing priming dose (holds the system onto the skin and protective peel strip
- Used for motion sickness as antiemetic applied to the post-auricular area
- Transderm-Nitro, Nitrodur, Nitrodisc, Deponit, Minitran
- Used once a day in the prophylaxis of angina pecroris (not for attacks) applied to the chest or upper arm
- Catapress TTS
- Used to treat hypertension
- One patch maintains 7 days of constant blood levels
- Estraderm, Vivelle
- Used for problems during menopause, ovary failure, hypogonadism, provides 4 days constant blood levels
- Potent analgesic used in chronic pain such as cancer, 72 hours effective
- 5% surface anesthesia, 12 hour relief, 12 hour on-off use
- Several brand names available
- Used for cessation of smoking
What are rate controlling systems like transdermal patches intended to do?
- Deliver drug at a controlled rate to intact skin without buildup in the dermal layers (skin is not target)
- Rlease the drug promptly from the system into the S. Corneum for penetration into the general circulation (systemic effects)
- Cause occlusion of the skin so there is only one way flux of drug, therapeutic advantage over other dosage forms (nothing is lost)
- Cause no irritation or sensitization to the skin due to drug vehicle or adhesive
- Increase patient compliance (size and color)
- Design must avoid proliferation of bacteria under occluded skin
What are some examples of drugs in a matrix system?
What are some examples of drugs in a reservoir system?