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What are some factors that influence percutaneous absorption?
- Physical and chemical properties of drugs
- Pharmaceutical vehicle
- Condition of the skin
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What is percutaneous absorption?
Absorption of substances from outside the skin to underneath the skin, including enterance into the blood stream
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What are the layers of the skin from outer to inner most?
- Epidermis: Stratum Corneum, Stratum Lucidum, Stratum Germinativum
- Dermis
- Subcutaneous
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What is another name for the stratum conreum?
- Horny layer.
- This is where Keratin is contained
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The stratum lucidum is also called?
Stratum granulosum
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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
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Are there several layers of epithelia cells?
Yes and they are at different stages of differentiation
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T/F
The skin is covered by an emulsified film of sebum, sweat, and dead celss that are constantl desquamating (peeling)
True
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Describe the statum lucidium
- aka Stratum Granulosum
- Barrier layer with living cells at several differentiated levels
- Living epidermis
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Describe the Statum Germinativum
- Living epidermis
- Has basal layer separating from dermis
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Describe the dermis
Vascularized tissue that drug must reach
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What is transdermal absorption?
From skin into circulation
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Define transcellular
- across
- Lipid-rich, non-polar drugs
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Define intercellular
- between
- Channels are the major route of drug penetration; polar drugs
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Define trans-appendegeal
- Across skin appendages
- Hair follicles, sweat glands, sebaceous glands, minor drug absorption
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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
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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)
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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)
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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)
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Percutaneous absorption can be enhanced through what two methods?
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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
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What solvents are exmaples of chemical percutaneous enhancers?
- Water
- Alcohols (methanol, ethanol, 2-propanol)
- Alkyl methyl sulfoxides (DMSO, decyl methyl sulfoxide, others)
- Pyrrolidones (2-pyrrolidone, n-methyl-2-pyrrolidone, others)
- Laurocapram (Azone)
- Urea
- N,N-diethyl-m-toluamide
- Miscellaneous (acetone, dimethyl acetamide, dimethyl formamide, etc)
- Amphiphiles
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What are amphiphiles?
- Both sides, polar and nonpolar
- Anionic surfactants
- Cationic surfactants
- Amphoteric suractants
- Nonionic surfactants
- Fatty acids and alchols
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What are some examples of anionic surfactants?
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What are some examples of cationic surfactants?
- Quaternary ammonium salts
- Also preservative
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What are examples of amphoteric surfactants?
- Lecithins
- Cephalins
- Alkyl bentamines
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What are examples of nonionic surfactants?
mono, di and triglycerides
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What are some examples of alchols and fatty acids?
- Lauryl
- cetyl
- stearyl alcohols
- sorbitan
- PEG
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What are some physcial methods that enhance percutaneous absorption?
- Iontophoresis
- Sonophoresis
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Define iontophoresis
delivery of charge chemicals across the skin using electrical field
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Define sonophoresis
High-frequency ultrasound facilitates drug penetration through the Stratum Corneum
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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
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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
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What are the two different designs of TDDS?
- Monolithic system
- Membrane-controlled system
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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)
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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
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Scopolamine
- Transderm-SCOP
- Used for motion sickness as antiemetic applied to the post-auricular area
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Nitroglycerine
- 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
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Clonidine
- Catapress TTS
- Used to treat hypertension
- One patch maintains 7 days of constant blood levels
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Estrogen
- Estraderm, Vivelle
- Used for problems during menopause, ovary failure, hypogonadism, provides 4 days constant blood levels
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Fentanyl
- Duragesic
- Potent analgesic used in chronic pain such as cancer, 72 hours effective
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Lidocaine
- Lidoderm
- 5% surface anesthesia, 12 hour relief, 12 hour on-off use
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Nicotine
- Several brand names available
- Used for cessation of smoking
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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
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What are some examples of drugs in a matrix system?
- Estradiol
- Fentanyl
- Methylphenidate
- Nicotine
- Nitroglycerin
- Oxybutynin
- Rivastigmine
- Ritigotine
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What are some examples of drugs in a reservoir system?
- Clonidine
- Estradiol
- Fentanyl
- Nicotine
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