THEORY OF DISSOLUTION AND VARIOUS DISSOLUTION APPARATUS

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THEORY OF DISSOLUTION AND VARIOUS DISSOLUTION APPARATUS

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THEORY OF DISSOLUTION AND VARIOUS DISSOLUTION APPARATUS Presented by: N.PAVAN M.Pharm – 1 st year Regd no.11AB1S0311 Under the guidance of: Mr. G. KISHORE BABU Asso.Prof Vignan pharmacy college Vadlamudi, Guntur

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Dissolution : it is a process in which a solid substance solubilizes in a given solvent i.e. mass transfer from the solid surface to the liquid phase Rate of dissolution is the amount of drug substance that goes in solution per unit time under standardized conditions of temperature, pH and solvent composition and constant surface area.

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The process involved in dissolution of solid dosage forms:

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Initial mechanical lag Wetting of dosage form Penetration of dissolution medium Disintegration Deaggregation Dissolution Occlusion of some particles MECHAMISM OF DISSOLUTION

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INTRINSIC DISSOLUTION The rate of dissolution of a pure pharmaceutical active ingredient when conditions such as Surface area , temperature, agitation or stirring speed , kept constant pH, ionic strength This parameter allows the screening under various bio physiological conditions IDR should be independent of boundary layer thickness and volume of solvent. Thus IDR measures the intrinsic properties of the drug only as a function of the dissolution medium, e.g. its pH, ionic strength, counters ions etc.

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Diffusion layer model/Film Theory Danckwert’s model/Penetration or surface renewal Theory Interfacial barrier model/Double barrier or Limited solvation theory.

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DIFFUSION LAYER MODEL/FILM THEORY :- It involves two steps :- Solution of the solid to form stagnant film or diffusive layer which is saturated with the drug Diffusion of the soluble solute from the stagnant layer to the bulk of the solution; this is rate-determining step in drug dissolution . Noyes and Whitney’s equation dc dt = k (C s - C b ) DAK w/o (C s – C b ) Vh dC dt = Modified N oyes – Whitney’s

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ii Danckwert’s model/Penetration or surface renewal Theory :- Danckwert did not approve of the existence of stagnant layer Danckwert takes into account consisting of macroscopic mass of eddies or packets These packets get continuously replaced by new ones and expose to new solid surface each time, thus the theory is called surface renewal theory .

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Interfacial barrier model (double barrier or limited salvation theory) Based on solvation mechanism and is a function of solubility rather than diffusion. When considering the dissolution of the crystal will have a different interfacial barrier given by following equation, G = ki (Cs – Cb ) Where G = dissolution per unit area Ki = effective interfacial transport constant The interfacial barrier model can be extended to both diffusion layer model and the Danckwert’s model.

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Based on presence of sink or non sink conditions dissolution apparatus are classified as 1.Closed compartment apparatus 2.Open compartment apparatus There are basically three general categories of dissolution apparatus : Beaker methods Open flow-through compartment system Dialysis concept

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APPARATUS CLASSIFICATION IN THE USP Apparatus 1 ( rotating basket ) Apparatus 2 ( paddle assembly ) Apparatus 3 (reciprocating cylinder ) Apparatus 4 (flow-through cell ) Apparatus 5 ( paddle over disk ) Apparatus 6 (cylinder ) Apparatus 7 (reciprocating holder ) Intrinsic dissolution (apparatus 1087)

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Apparatus Classification in the EUROPEAN PHARMACOPOEIA for Different Dosage Forms A) For solid dosage forms Paddle apparatus Basket apparatus Flow-through apparatus B) For transdermal patches Disk assembly method Cell method Rotating cylinder method C) For special dosage forms Chewing apparatus (medicated Chewing gums), Flow-through apparatus, Apparatus Classification in the INDIAN PHARMACOPOEIA Apparatus 1 : Paddle type B) Apparatus 2 : Basket type :

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APPARATUS 1- BASKET APPARATUS a)Vessel :- Made up of borosilicate glass -Semi hemispherical bottom -Capacity 1000ml b)Shaft : -Stainless steel 316 -Rotates smoothly without significance wooble c)Basket :- Stainless steel 316 -Gold coatings up to 0.0001 inch d)Water bath : Maintained at 37±0.5⁰c Use : Capsules , tablets, delayed release, suppositories , floating dosage forms

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Two basket attachment designs: On the left is the O-ring design and on the right is the three-pronged USP Apparatus 1 design

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1.Vessel : Made up of borosilicate glass -Semi hemispherical bottom -Capacity 1000ml 2.Shaft: The blade passes through shaft so that bottom of blade fuses with bottom of shaft . 3.Stirring elements :- Made of Teflon -For laboratory purpose -Stainless steel 316 4.Water bath : Maintain at 37±0.5⁰c 5.Sinkers: Platinum wire used to prevent capsule /tablet from floating APPARATUS 2 : PADDLE TYPE:

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The sinker required in the Japanese Pharmacopeia .

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Hollow shaft auto sampler. (Courtesy of SotaxCorporation , Horsham, Pennsylvania, U.S.A.)

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PEAK VESSEL This vessel is designed to eliminate “coning ’’ by having a cone moulded into the bottom of the glass vessel Peak vessel. (Courtesy of VanKel, a member of the Varian, Inc . Life Science Business, Cary, North Carolina, U.S.A.)

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Water bath-less dissolution apparatus A water-less bath method is alternative way to heat the vessels other than a conventional water bath the vessels are heated with a water jacket and are not submerged into a water bath.

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Deaeration equipment. (Courtesy of Distek, Inc., North Brunswick, New Jersey, U.S.A.) Air bubbles can : interfere with the result Can cause particles to cling to the apparatus and vessel walls Deaeration can be done by: Heating Filtering Vacuum Deaeration

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The assembly consists of a 1)set of cylindrical flat-bottomed glass vessels 2 )set of glass reciprocating cylinders; 3 )stainless steel fittings(type 316) and screens that are made of suitable nonsorbing and nonreactive material(polypropylene) and a motor and drive assembly to reciprocate the cylinders vertically inside the vessels Apparatus III – Reciprocating cylinder

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The vessels are partially immersed in a suitable water bath of any convenient size that permits holding the temperature at 37 ± 0.5 during the test. The dosage unit is placed in reciprocating cylinder & the cylinder is allowed to move in upward and downward direction constantly. Release of drug into solvent within the cylinder measured. Useful for: Tablets , Beads , controlled release formulations Standard volume: 200-250 ml/station Advantages : 1) Easy to change the pH-profiles 2) Hydrodynamics can be directly influenced by varying the dip rate. Disadvantages: 1) small volume (max. 250 ml) 2) Little experience 3) Limited data

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Apparatus 3 – Reciprocating cylinder

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USP Apparatus 4 - Flow Through Cell

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The assembly consists of a reservoir and a pump for the Dissolution Medium; a flow-through cell; a water bath that maintains the Dissolution Medium at 37 ± 0.5 The pump forces the Dissolution Medium upwards through the flow-through cell. Assemble the filter head, and fix the parts together by means of a suitable clamping device. Introduce by the pump the Dissolution Medium warmed to 37 ± 0.5 through the bottom of the cell to obtain the flow rate specified in the individual monograph. Collect the elute by fractions at each of the times stated. Perform the analysis as directed in the individual monograph

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Useful for: Low solubility drugs , Micro particulates, Implants , Suppositories , Controlled release formulations Variations: (A) Open system & (B) Closed system Advantages: 1. Easy to change medium 3. Sink conditions Disadvantages: 1. Deaeration necessary 2. High volumes of medium

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Apparatus 4 – Flow-Through Cell

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USP Apparatus 5 - Paddle Over Disk

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Use the paddle and vessel assembly from Apparatus 2 with the addition of a stainless steel disk assembly designed for holding the transdermal system at the bottom of the vessel. The disk assembly holds the system flat and is positioned such that the release surface is parallel with the bottom of the paddle blade The vessel may be covered during the test to minimize evaporation. Useful for: Transdermal patches Standard volume : 900 ml Disadvantages: Disk assembly restricts the patch size. Borosilicate Glass 17 mesh is standard (others available) Accommodates patches of up to 90mm

USP Apparatus 6 - Cylinder:

USP Apparatus 6 - Cylinder 34

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• Use the vessel assembly from Apparatus 1 except to replace the basket and shaft with a stainless steel cylinder stirring element • The temperature is maintained at 32°C ± 0.5°C • The dosage unit is placed on the cylinder with release side out The dosage unit is placed on the cylinder at the beginning of each test, to the exterior of the cylinder such that the long axis of the system fits around the circumference of the cylinder & removes trapped air bubbles. Place the cylinder in the apparatus, and immediately rotate at the rate specified in the individual monograph. 35

USP Apparatus 7 – Reciprocating Holder :

USP Apparatus 7 – Reciprocating Holder 36

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The assembly consists of a set of volumetrically calibrated solution containers made of glass or other suitable inert material, a motor and drive assembly to reciprocate the system vertically • The temperature is maintained at 32°C ± 0.5°C • The dosage unit is placed on the cylinder with release side out The solution containers are partially immersed in a suitable water bath of any convenient size that permits maintaining the temperature, inside the containers at 32 ± 0.5 For Coated tablet drug delivery system attach each system to be tested to a suitable Sample holder 37

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For Transdermal drug delivery system attach the system to a suitable sized sample holder with a suitable O-ring such that the back of the system is adjacent to and centered on the bottom of the disk-shaped sample holder or centered around the circumference of the cylindrical-shaped sample holder. Trim the excess substrate with a sharp blade. 38

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I.P. USP B.P. E.P. Type 1 Paddle apparatus Basket apparatus Basket apparatus Paddle apparatus Type 2 Basket apparatus Paddle apparatus Paddle apparatus Basket apparatus Type 3 Reciprocating cylinder Flow through cell apparatus Flow through cell apparatus Type 4 Flow through cell apparatus Type 5 Paddle over disk Type 6 cylinder Type 7 Reciprocating holder

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USP APP. DESCRIPTION ROT. SPEED DOSAGE FORM Type 1 Basket apparatus 50-120rpm IR, DR, ER Type 2 Paddle apparatus 25-50rpm IR, DR, ER Type 3 Reciprocating cylinder 6-35rpm IR,ER Type 4 Flow through cell apparatus N/A ER , poorly soluble API Type 5 Paddle over disk 25-50rpm TRANSDERMAL Type 6 cylinder N/A TRANSDERMAL Type 7 Reciprocating holder 30rpm ER

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Vessel head for sampling.

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Automated filter assembly .

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Fully automated custom system

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Fully automated dissolution system.

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Calibration or Apparatus Suitability Test USP calibrator tablets, prednisone and salicylic acid .( Courtesy of Erweka, GmbH, Heusenstamm, Germany.) Pharmaceutical Research Manufacturers of America (PhRMA) formerly known as Pharmaceutical Manufacturers of America (PMA ) conducted the collaborative studies

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CONCLUSION : B y conducting dissolution studies we can know the batch to batch reproducibilit y We can estimate the solubility profiles of drugs The best available tool today which can at least quantitatively assure about the biological availability of drug from its formulation is its invitro dissolution

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Pharmaceutical Dissolution Testing - Taylor & Francis Remington The science and practice of pharmacy 21 st edition volume 1 Leon Shargel, Applied Biopharmaceutics & Pharmacokinetics; Alton’s pharmaceutics - The design and manufacturing of medicines D.M.Brahmankar, Bio pharmaceutics and pharmacokinetics A Treatise; Vallabh Prakashan www.://apps.who.int/phint/en/p/docf / Us pharmacopeia Indian pharmacopeia REFERENCES .

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