Transdermal drug delivery systems

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2 : CONTENTS Introduction Structure of the skin Pathways of drug absorption Advantages and disadvantages Transdermal Absorption flux Factors that influence TDD Transdermal Therapeutic Systems Components of TDDS Testing of TTS Advances in TDDS Marketed products Conclusion References 2
3 : Introduction Transdermal drug delivery is the delivery of drugs through the skin to elicit a systemic effect. Redefined as one that delivers drugs through the skin to elicit ‘regional’ or ‘systemic’ effects. Transdermal drug delivery system can deliver the drugs through the skin portal to systemic circulation at a predetermined rate and maintain clinically the effective concentrations over a period of time. 3
4 : Structure of the skin Fig.1(a): The different layers of the skin Fig.1(b):Basic anatomy of human skin 4
5 : Pathways of drug absorption Fig.2: pathways of drug absorption 5
6 : advantages & Disadvantages Avoids first pass metabolism and Better Patient compliance Prolonged duration of action Effective use of drugs with short half life Suitability for self administration Minimized adverse effects due to a steady and optimum blood concentrations Ease of terminating the drug therapy if necessary Poor permeability of the human skin limits the daily dose of the drug delivered Local irritation at site of administration Not a means to achieve rapid bolus type drug inputs Drug degradation may occurs due to enzymes produced by the microbial population of skin surface 6
7 : Transdermal flux The permeability coefficient at steady state of the skin to the drug is defined by -Ks is the partition coefficient for the interfacial partitioning of the drug molecule fromTDDS into SC - Dss is the diffusivity of drug molecule through the skin tissue -hs is the overall thickness of the skin tissue At steady state , the flux is given by -Jss is the steady flux(mg/cm2 /hr )and Cveh is the drug conc. In the vehicle or formulation(mg/cm2) 7 Pss = Ks Dss /hs Jss = Pss. Cveh
8 : Factors that influence TDD Physicochemical factors Solubility Molecular size Lipophilicity Ionisation of the drug Melting point Biological factors Dose of the drug Cutaneous side effects Elimination half life of the drug Stability of the drug in the skin tissue 8
9 : Transdermal Therapeutic Systems Membrane controlled systems Adhesive diffusion-controlled systems Matrix- type &single layer drug in adhesive- type systems Multilayer drug in adhesive systems Micro reservoir-type systems 9
10 : Membrane controlled TDDS 10 Fig.3: Different layers of membrane controlled (reservoir-type) transdermal drug delivery system
11 : Adhesive diffusion-controlled systems 11 Backing membrane Drug in adhesive Release liner Rate controlling adhesive layer Fig.4:different layers of adhesive diffusion- controlled TDDS
12 : Matrix-type & single layer drug in adhesive-type TDDS 12 Backing membrane Drug in polymer adhesive adhesive Release liner Backing membrane Drug in adhesive Release liner Fig.5(a):Matrix-type transdermal systems fig.5(b): Single layer drug in adhesive-type transdermal systems
13 : Multilayer adhesive systems 13 Backing membrane Drug in adhesive for immediate release Rate controlling membrane Release liner Drug in adhesive for controlled release Fig.6: Different layers in Multilayer drug adhesive system
14 : Micro reservoir-type systems 14 Backing membrane Drug in liq.polymer solution dispersed in lipophilic polymer adhesive Release liner adhesive Fig.7: A typical Micro reservoir system
15 : Components of TDDS Drug Polymer matrix or matrices that regulate the release of the drug Natural and semisynthetic- CMC, CAP, EC, Gelatin, Starch, Shellac etc. Synthetic elastomers- Polybutadiene, neoprene etc. Synthetic polymers- PVA, Polyethylene, Polypropylene etc. Adhesives PIB-based adhesives Acrylic adhesives Silicone- based adhesives 15
16 : Components of TDDS continued……… Penetration enhancers Chemical Solvents –DSMO, Ethanol and micellar solutions -disruption of SC lipid organisation making it more permeable. -changing the solution properties of SC by altering the chemical environment Ionic surfectants- Decylmethylsulphoxide -interacts with the keratin of corneocytes to open up the dense protein structure and make them more permeable. Physical means of penetration enhancement -Iontophoresis, Electroporation , Sonophoresis, Photomechanical waves and Magnetophoresis 16
17 : Components of TDDS continued……… Release liner -peeled off before use. -prevents loss of drug that has migrated into the adhesive layer during storage and protects the final device from contamination. -polyesters and metal foils. Backing membrane -must be flexible and provide good bonding to the drug reservoir -polyesters-polyethylene coextruded films Packaging substrates – unit doses in sealed pouches 17
18 : Testing of Therapeutic transdermal systems Physicochemical Thickness- travelling microscope, dial gauge, screw gauge and micrometer. Wieght uniformity Drug content %Moisture loss- desiccator withCaCl 2 at 40o/24hrs. - %Moisture loss =initial wt-final wt/initial wt*100 %Moisture absorbed –Saturated solution of Alcl3 at 79.50%RH /3 days - %Moisture uptake = final wt-initial wt/initial wt*100 Folding endurance 18
19 : Testing of Therapeutic transdermal systems continued……… In vitro Drug release studies: -cellophane membrane -Diffusion for 24 hrs.- Franz diffusion cell( vertical as well as horizontal), Flow-through cells Ex Vivo permeability studies: -Skin irritation test in rats -Permeability studies in rats Preclinical In Vivo Evaluation: -Absorptio in the pig and monkey appears more predctive of in vivo data in humans 19
20 : Advances in TDDs continued………. Iontophoresis is the application of an electric power source that charges the drug substance and facilitates the movement of these charged drugs to move into the skin. 20 Fig.8: principle involved in iontophoresis
21 : Advances in TDDs continued…….. The Transcu active iontophoresis transdermal drug delivery system rely on the principle of iontophoresis which includes the use of external electrical sources to deliver drugs non-invasively through the skin, controlling the rate and duration of drug delivery. The Transcu passive ionic transdermal drug delivery system is a simple, relatively inexpensive and optimised enhancer patch system that can accelerate the delivery of larger ‘ionic’ or electrically charged drugs which other conventional systems cannot effectively deliver. 21
22 : Advances in TDDs continued……….. Electroporation or electropermeabilisation is the transitory structural pertubation of lipid bilayer membranes by the application of high voltage pulses – 30-100 V (100-1500 V). New aqueous pathways would then be created within the SC due to electroporation of its lipid bilayer. Could be used for a rapid and pulsed delivery of drugs and therapeutic macro molecules. 22
23 : Advances in TDDs continued…… Sonophoresis : Use of ultra sound waves of frequency less than 18kHz. Transdermal transport during application of low frequency ultrasound occurs across keratinocytes than hair follicles. Longitudinal sound waves cause compression and expansion in the medium resulting in cavitation , thermal effects and mechanical effects. Incase of SC, this can results into formation of aqueous channels through the intercellular lipids through which drugs can permeate easily. 23
24 : Advances in TDDs continued….. Photomechanical waves: A drug solution is placed on the skin and covered by a black polystyrene target. It is then irradiated with a laser pulse. The resultant photomechanical wave stresses the horny layer and enhances drug delivery. Magnetophoresis: Involves the movement of diamagnetic materials through the skin The mechanism facilitating the drug absorption is magnetohydrokinesis. 24
25 : Advances in TDDs continued…….. Microstructured systems Individual silicon needles(approx.400) of approximately 150µm length and 80µm base diameter are fabricated on 3*3mm arrays. Designed to create a physical pathway through the upper epidermis to increase skin permeability. Enables the disruption of outermost layer of the skin, the SC, without causing pain. Suitable for vaccines and protein or peptide-based drugs. 25
26 : Marketed products 26
27 : conclusion Today, the use of the skin as a route of drug delivery is well established and research into the development of devices for optimum drug delivery is underway. Curently, a few transdermal patches do exist for drugs such as scopalamine, lidocaine, fentanyl etc. Various approaches such as chemical enhancers, electricity, ultrasound and microneedles are being explored for the delivery of macromolecules. Further research will undoubtedly be aimed at better transdermal devices design, development of novel methods and techniques and the assesment of safety and efficacy of existing technologies for delivering a wide variety of molecules. 27
28 : references S.P.Vyas, R.K.Khar;Targetted and controlled Drug Delivery-novel carrier systems, Volume-II: 28-45. N.K.Jain; Advances in Controlled and novel drug delivery ,2007. Joseph R.Robinson, Vincent H.L.Lee;Controlled drug delivery – Fundementals and applications,second edition, Revised and expanded:523-553. P.K.gaur:s.Mishra,S.puronit,K.dave: Transdermal drug delivery systems, a review, Asian journal of pharmaceutical and clinical research 2010. 28
29 : 29 Thank u


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