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Tdds

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methods of formulation, evaluation and iontophorosis

Veröffentlicht in: Gesundheit & Medizin
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Tdds

  1. 1. Advantage: 1. Avoidance of first pass effect 2. Stable and controlled blood level 3. Comparable characteristics with intravenous infusions. 4. Long term duration 5. No interferance with gastric and intestinal fluids. 6. Administer drugs with very short half life, narrow therapeutic window and poor oral absorption. 7. Improved patient compliance. 8. Self administration is possible. 9. Systems are noninvasive.
  2. 2. Limitations: 1. Drug must have desirable physicochemical properties for permeation through stratum corneum. 2. Skin irritation or contact dermatitis due to drug or excipients. 3. Barrier function of skin changes from one site to another on the same person, person- to-person and with the age of person.
  3. 3. PERMEATION OF DRUG MOLECULE THROUGH SKIN • It express by Fick’s first law of Diffusion-Drug molecule diffuse from a region of higher conc. to one of lower conc. until equilibrium is attained. • The process of Diffusion of molecule is driven by gradient between high concentration to low concentration. 10
  4. 4. PERCUTANEOUS ABSORPTION
  5. 5. • Percutaneous absorption done by 2-ways- A. Transepidermal Absorption Stratum Corneum Intracellular Pathway Intercellular Pathway Viable Epidermis Dermis Microcirculation
  6. 6. • B. Transfollicular Absorption Pilosebaceous unit Eccrine Gland Hair Follicles Sebaceous Gland Dermis Microcirculation
  7. 7.  Skin appendages offer only secondary route of permeation.  The follicular route is important route of percutaneous absorption since the opening of follicular pore where the hair shaft exits the skinis relatively large and sebum aids in diffusion of penetrants.
  8. 8. Steps involved in transdermal permeation of drug:- 1. Sorption by stratum corneum 2. Penetration of drug through viable epidermis 3. Uptake of drug by capillary network in the dermal papillary layer.
  9. 9.  Physicochemical property of Drug molecule,  Partition co-efficient,  pH Condition,  Drug Concentration  Physicochemical property of Drug Delivery System, Release characteristics, Use of permeation enhancer, Composition of Drug Delivery System. 17
  10. 10.  Pathophysiological condition of Skin, Reservoir effect of Horney Layer, Hydration of skin, Lipid Film, Skin Temperature, 18
  11. 11. 1. Partition coeff. : Drugs possessing both water and lipid solubilities are favored .  Lipid/water partition coeff. of 1 or more is required for optimal transdermal permeability. 2. pH conditions: pH conditions of skin and in drug delivery system affect dissociation and permeation of drug molecule. 3. Drug concentration: permeation is passive diffusion process hence depends on drug conc. on surface of skin layer.  more drug is absorbed through percutaneous absorption when the drug is applied to a large surface area.  Drug incorporated in an appropriate vehicle must interface skin in sufficient concentration.
  12. 12. 1. Release characteristics: generally the more easily the drug is released from delivery system, the higher the rate of permeation.  Drug subs. should have greater physicochemical attraction to skin than to vehicle in which it is presented in order for the drug to leave in favor of the skin.  Mechanism of depends on interfacial partition coeff. of drug from delivery system to skin tissue. 2. Composition of drug delivery system: it has great influence on absorption.  It not only affect release rate but also permeability of stratum corneum by means of hydration, mixing with skin lipids or other promoting effects.
  13. 13. 3. use of permeation enhancers: permeation can be improved by use of sorption or permeation promoters.  Drug absorption enhanced by the vehicles that easily cover the skin surface, mix readily with sebum and bring drug in contact with sebum for tissue absorption.
  14. 14. 1. Reservoir effect of horny layer: horny layer or its deep layer can act as depot or reservoir.  Absorption appears to be greater when drug is applied to skin with thin horny layer than with one that is thick. thus, site of application affect degree of drug absorption.  Generally, longer the period of time of medicated application is permitted to remain in contact with skin, the greater will be the absorption.
  15. 15. 2. Vehicles that increase amount of moisture imbedded by the skin generally favor percutaneous absorption of drug. Oleaginous vehicles acts as moisture barrier through which the sweat from the skin cannot pass and skin therefore remain occluded resulting in increased hydration of skin beneath the vehicle. 3. Skin hydration: imp factor of absorption.  hydration of stratum corneum appears to increase rate of passage of certain substances that penetrate the skin.  Increased absorption is probably due to softening of the tissues and the consequent sponging effect with an increase in size of the pore allowing greater flow of substance, large and small molecules through them.
  16. 16.  Hydration of stratum corneum can enhance the permeability of skin by as much as eight folds. 4. Skin temperature: skin permeation of acetyl salicylic acid and glucosteroids was raised ten folds when the environmental temp was raised from 10- 37 °C.
  17. 17. Permeation enhancers may be:- 1. Solvents: increase penetration by swelling the polar pathway. Eg, alcohols, dimethylsulfoxide (DMSO), dimethylformamide, 2-pyrrolidone etc. 2. Surfactants: enhance polar pathway transport of hydrophillic drugs. Eg, sodium lauryl sulfate, Pluronic F127, Pluronic F68 3. Bile salts: sodium deoxycholate, sod. taurocholate.
  18. 18. A. Rate-Programmed Systems  Drug in Reservoir  Drug in Matrix  Drug in Adhesive  Drug in Microreservoir 34 B. Physical Stimuli- Activated Systems Iontophoresis
  19. 19. 1.Drug in Reservoir A.RATE-PROGRAMMED SYSTEMS- -Drug reservoir is embedded between an impervious backing layer and a rate controlling membrane. -Drug release only through the rate controlling membrane. -In drug reservoir compartment, it can be in the form of solution, suspension or gel or dispersed in a solid polymer matrix. -On the outer surface of polymer membrane a thin layer
  20. 20. 2.Drug in Matrix •The drug is dispersed homogenously in a hydrophilic or lipophilic polymer matrix. •This drug containing polymer layer is then fixed onto an occlusive base plate in a compartment fabricated from a drug impermeable backing layer. •Instead of applying adhesive on the face of the drug reservoir, it is spread along the circumference to form a strip of adhesive rim.
  21. 21. 3.Drug in Adhesive Here, adhesive layers are also responsible for releasing of drug. Drug reservoir is formd by dispersing drug in adhesive polymer and then spreading medicated polymer adhesive by different methods on impermeable backing membrane.
  22. 22. 4.Drug in Microreservoir -It is a combination of reservoir and matrix dispersion system. - For drug reservoir, the drug is first suspended in aqueous solution of water soluble polymer and then dispersing the solution homogenously in lipophillic polymer to form thousands of unleachable, microscopic spheres of drug reservoir.
  23. 23. B. Physical Stimuli-Activated Systems- 1. Iontophoresis- It involves transport of ionic or charged molecules into a tissue by a passage of direct or alternating electric current through electrolyte solution containing the ionic molecules to be delivered. It involves electromotive force for transfer of ions.
  24. 24.  Ions with positive charge are driven into the skin at the anode and those with negative charge at the cathode.  Drug is administered through an electrode having same charge as that of drug and a return electrode opposite to charge of drug.  Operator then selects current intensity below the pain threshold level of the patient and allows the current to flow for an appropriate period of time.  Current intensity should be increased slowly , maintained for the length of the treatment and then slowly decreased at the end of the treatment.  Current must be between the tolerance of the patient with a current density less than 0.5 m.amp/cm2 of the electrode surface.
  25. 25.  Placing a moist pad between electrode plate and the skin is necessary for making perfect contact, preventing any skin burns, overcoming skin resistance and protecting the skin from absorbing any caoustic metallic compound formed on the metal plate surface.  The drug should be applied through the electrode with correct polarity , since any reversal of polarity may result in no penetration of the drug.
  26. 26. 1. Evaluation of Adhesive a. Peel Adhesion Properties-  It is the force required to remove coating from a test substrate.  peel adhesion properties are affected by molecular weight of adhesive polymer , type and amount of additives ad polymer composition. 42
  27. 27. Tack Properties- It is the ability of polymer to adhere to a substrate with little contact pressure.  Thumb tack test- press thumb briefly on the adhesive.  Rolling ball tack test – measurement of distance that a stainless steel ball travels along an upward facing adhesive. the less tacky the adhesive, father the ball will travel.
  28. 28.  Quick-Stick test/ peel tack test- peel force required to break he bond between the adhesive and substrate is measured by pulling the tape away from substrate at 90° at speed of 12 inch/min. force is recorded as tack value and expressed in ounce per inch width.
  29. 29.  Probe tack test: force required to pull a probe away from the adhesive at a fixed rate is recorded as tack.
  30. 30. c. Shear Strength Properties- It is the measurement of the cohesive strength of an adhesive polymer. Shear strength is determined by measuring the time it takes to pull an adhesive coated tape off a stainless steel plate when a specified weight is hung from the tape which pulls tape in a direction parallel to the plate.
  31. 31. A. In vitro Permeation Studies-  In-Vitro skin Diffusion cells B. In vitro Release Studies-  Paddle Over Disc Apparatus (USP Apparatus 5)  Reciprocating Disc (USP Apparatus 7). 47

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