Invitro : dissolution and drug release testing

Dissolution : Official and Non official methods, Alternative methods of dissolution testing and transport models, Drug release testing, Invitro drug release testing

1. In vitro : Dissolution and drug release testing Presented by: Durgadevi.G 1 st M.pharm . Dept. of pharmaceutical analysis, PSG college of pharmacy.

2. DISSOLUTION : Dissolution is a process in which a solid substance solubilizes in a given solvent (mass transfer from the solid surface to the liquid phase.) Dissolution testing measures the extent and rate of solution formation from a dosage form, such as tablet, capsule, ointment, etc. The dissolution of a drug is important for its bioavailability and therapeutic effectiveness .

3. DISSOLUTION RATE : Dissolution rate is defined as the amount of solid substance goes into solution per unit time under standard conditions of temperature, pH and solvent composition and constant surface area. ABSOLUTE OR INTRINSIC SOLUBILITY : It is defined as the maximum amount of solute dissolved in a given solvent under standard conditions of temperature, pressure and pH.

4. DISSOLUTION OF TABLETS AND CAPSULES When a immediate release tablet or other solid drug form is introduced into a beaker of water or into the gastrointestinal tract, the following steps take place. Disintegration : breaking of tablet into granules. Deaggregation : breaking of these granules into individual particles. Dissolution : finally, particles dissolve, releasing the active drug into solution. Dissolution is a time dependant process that represents the final step of drug release, which is ultimately required before a drug can be absorbed or exert a pharmacologic effect.

5. Name of Apparatus Drug product Rotating basket tablets Paddle Tablets, capsules, modified release products, suspensions. Reciprocating cylinder Extended release drug products Flow cell Low water soluble drugs Paddle over disk Transdermal drug products Cylinder Transdermal drug products Reciprocating disk Extended release drug products Rotating disk Extended release drug products OFFICIAL METHODS (USP) :

6. ROTATING BASKET METHOD Cylindrical basket of 22mesh. Rotating speed-100 rpm. As per IP, height of dissolution jar is 168+8 mm and internal diameter is 102+4 mm and height of basket 36.8+3 mm and diameter is 25.4+3 mm. Temp. maintained at 37ᵒC Calibration tablets of Prednisone-for disintegrating tablets. Salicylic acid calibration tablets-for non disintegrating tablets. For capsules & dosage forms that tend to float.

7. PADDLE METHOD  It consists of a special coated paddle formed from a blade and a shaft that minimizes turbulence due to stirring. The coated material is inert. The paddle is attached vertically to a variable -speed motor that rotates at a controlled speed.

8. As per IP, diameter of the paddle is 74.5+0.5 mm. The tablet or capsule is placed into a round-bottom dissolution flask and the apparatus is housed in a constant temperature water bath maintained at 37°C. Most common operating speeds are 50rpm for solid oral dosage forms and 25 rpm for suspensions. A sinker ,such as few turns of platinum wire may be used to prevent a capsule or tablet from floating Used for film coated tablets that stick to the vessel walls or to help to position tablet/capsule under the paddle.

9. RECIPROCATING CYLINDER METHOD Set of cylindrical, flat –bottomed glass vessels equipped with reciprocating cylinders. temp. 37ᵒC Place the stated volume of dissolution medium in each vessel of the apparatus, assemble the apparatus, equilibrate the dissolution medium to 37±0.5ᵒC and remove the thermometer

10. Place one dosage form unit in each of the cylinders taking care to exclude the air bubbles from the surface of each dosage unit and immediately operate the apparatus as specified in the monograph. During the upward and downward stroke, the reciprocating cylinder moves through a total distance of 9.9 to 10.1cm. Within the time interval specified raise the cylinders and withdraw a portion of the solution under test from a zone midway between the surface of the dissolution medium and bottom of each vessel.

11. FLOW THROUGH CELL METHOD The flow through cell is transparent & inert mounted vertically with filters. Standard cell diameters are 12 & 22.6 mm. The bottom cone usually filled with glass beads of 1 mm diameter. Place the glass beads into the cell as specified in the monograph. Place one dosage unit on top of the beads or on a wire carrier.

12. Tablet holder used for positioning special dosage form e.g. inlay tablets. Assemble the filter head and fix the parts together by means of a suitable clamping device. Introduce by the pump of the dissolution medium warmed to 37±0.5ᵒC through the bottom of the cell to obtain the flow rate specified and measured with an accuracy of 5%. Flow rate is maintained from 4 to 16 mL /min. Collect the eluate by fractions at each of the times stated For modified release dosage forms, containing active ingredients with limited solubility.

13. PADDLE OVER DISK METHOD For testing the release of drug from transdermal products. Stainless steel disk assembly is used for holding the transdermal system at the bottom of the vessel. The distance between the paddle and the surface of the disk is kept 25 ± 2 mm . The release surface of the trans dermal patch is kept such that it’s release surface faces upward and parallel to the edges of the blade. The transdermal system may be attached to the disk assembly by applying a suitable adhesive. TEMP.- 32± 0.5 ºC. Sample is drawn midway between the surface of the dissolution medium and the top of the paddle blade. Dosage unit kept on disk assembly

14. ROTATING CYLINDER METHOD Here, basket and shaft are replaced by the cylinder stirring elements. The dosage unit is kept on the cylinder. The distance between the inside bottom of the vessel and the cylinder is kept at 25 ± 2 mm. TEMP .- 32± 0.5 ºC. Sample is mounted on to cuprophan . Temperature 32ᵒC For testing transdermal preparations. Inert porous cellulose support

15. RECIPROCATING DISK METHOD It consist of a set of volumetrically calibrated or tared containers of glass or other suitable inert material , a motor and a set of sample holders. A motor drive assembly is used to reciprocate the system vertically. Samples are placed on disk shaped holders using cuprophan supports. Temperature 32ᵒC. Reciprocating frequency is about 30cylces per minute. It is useful for assessing the in vitro dissolution of extended release tablets and transdermal drug delivery systems

16. NON OFFICIAL METHODS Tumbling method Rotating disk method Rotating bottle method Intrinsic dissolution method Peristalsis method Sartorius apparatus Beaker method Dialysis method

17. TUMBLING METHOD In this method dosage form is placed in tubes or bottles which are rotated using revolving drum. It consists of magnetically driven rotating filter assembly and a 12 mesh wire cloth basket in which dosage form is placed. The sample is withdrawn through spinning filter for analysis. ROTATING FILTER METHOD

18. ROTATING DISK METHOD Developed by late eino nelson and described by Levy and Sahli . Non disintegrating tablets or discs mounted in plexiglas holder, one surface exposed to the dissolution medium. Holder is attached to the metal shaft , free from vibration The tablet immersed one inch below the surface of 200 ml of dissolution fluid , temp 37ᵒc , in 500 ml three round bottom flask , rate is 550 rpm. Samples were taken and assayed for drug content.

19. SARTORIUS APPARATUS It utilize in vivo stimulative method The absorption stimulater stimulates passive drug transport process that occur in vivo from GIT tract to plasma across lipoidal mucosal barrier

20. ROTATING BOTTLE METHOD It consists of rotating rack to hold sample drug products in bottles and they are capped tightly and rotated in 37ᵒC temperature bath Sample are decanted through a 40 mesh screen and residue are assayed

21. INTRINSIC DISSOLUTION METHOD Most method for dissolution deal with finished drug product The dissolution of drug powder by maintaining constant surface area is called intrinsic dissolution. It is expressed as mg/cm²/min.

22. PERISTALSIS METHOD To stimulate hydrodynamic condition of GIT tract in an in vitro dissolution device. It consists of rigid plastic cylindrical tubing fitted with septum and rubber stopper at both ends. Dissolution chamber consist of a space between the septum and the lower stopper Dissolution medium pumped with peristaltic action through the dosage form

23. BEAKER METHOD Reported by Levy and Hayes(1960) Dissolution medium , 250 ml of 0.1 N HCl at 37ᵒC placed in a 400 ml beaker Agitation by three blade polyethylene stirrer,5 cm diameter and rotates at 60 rpm. Stirrer immersed to a depth of 2.7 cm in medium and in the center Samples are removed and assayed for the content.

24. DIALYSIS METHOD Cell consist of 32 mm inflated membrane Plugged at the lower end by tight fitting cylindrical perspex box. Upper end of the tube held by thin perspex ring inserted into the tube and secured by an elastic band The cell , suspended from the arm of a tablet disintegration apparatus and containing the dosage form in 50 ml of distilled water at 37ᵒC. The cell was raised and lowered 30 times a min into 150 ml of distilled water at same temp. Agitation by slight flexing and streching of the dialysis membrane as it enters and leave the bath Rotation at 60 rpm Samples taken and assayed for content.

25. ALTERNATIVE METHODS OF DISSOLUTION TESTING TRANSPORT MODELS NON SINK METHODS For poorly water-soluble drugs, pharmaceutical scientists are increasingly applying in vitro dissolution testing under non-sink conditions for a direct evaluation of their ability to generate and maintain supersaturation as a predictive surrogate for ensuring product quality and in vivo performance. NATURAL CONVECTION NON SINK METHODS: a) Klein solvmeter method b) Nelson hanging pellet method c) Levy static disk method FORCED CONVECTION NON SINK METHODS: a)Tumbling method b) Levy or Beaker method c) Rotating disk method d) Particle size method e) USP Rotating basket apparatus f) USP Paddle apparatus

26. SINK METHODS Sink condition  is the ability of the  dissolution  media to  dissolve  at least 3 times the amount of drug that is in your dosage form. Having  sink conditions  helps your  dissolution  have more robustness as well as being more biologically relevant. FORCED CONVECTION SINK DEVICES: a) Wurster pollis adsorption method b) Partition method c) Dialysis methods d) Rotating disk apparatus CONTINOUS FLOW/FLOW THROUGH METHODS: a) Pernarowski method b) Langenbucher method c) Baun and Walker d) Tingstad and Reigelman e) Modified column apparatus f) Takenaka method

27. KLEIN SOLVMETER METHOD Carrier device surrounded by flat and is immersed in dissolution medium When dosage form is placed in the boat the bar moves and as dosage form dissolves it moves upwards Amount of dosage form dissolved is revealed from the difference in height of bar movement 

28. NELSON HANGING PELLET METHOD  Aluminum strip having provision for holding dosage form which is in turn connected perfectly maintained balance arm of strip Dosage form is mounted on aluminium strip with help of wax .This method can be employed to know Intrinsic dissolution rate. To prevent disintegration further high pressures can be applied and also constant surface 

29. LEVY STATIC DISK METHOD Acrylic holder containing dosage form is inserted into a known volume of medium through rubber stopper The vial is inverted and placed in incubator at 37 C . At specific time intervals the vial is removed from incubator and samples are analysed Disadvantages :- effect of conc. On dissolution medium is ignored and the surface area of dosage form while dissolving is assumed constant which is not impractical .

30. WURSTER-POLLI ADSORPTION METHOD In this method the dissolved drug is adsorbed by charcoal or bentonite . care should be taken regarding the adsorbent, adsorbent should not alter the viscosity of the medium 

31. PARTITION METHOD  In this device organic phase is employed to remove the dissolved drug such that the drug would partition between the lipophilic and hydrophilic phases. selection of organic phase plays a critical role

32. ROTATING FLASK APPARATUS  In this method a flask containing dissolution medium is rotated around its horizontal axis in a water bath kept at a temperature of 37 C. The flask has a provision of sampling such that aliquots can be withdrawn and the fresh medium can be replaced back. This apparatus is best suited for oral solid dosage forms like tablets and capsules since they do not require much agitation . 

33. FLOW THROUGH DEVICES For the drugs which saturate rapidly in large volumes of medium, USP apparatus will not serve the purpose. For this the suitable device is flow through device. In this device unlimited quantity of fresh dissolution is available. A dosage form is placed in a small cell and is subjected to a stream of fresh dissolution media. 

34. PERNAROWSKI  It consists of 10 mesh stainless steel basket stirrer assembly with an adjustable stirrer. the chamber is 3 necked flask of 33 mm and the rest two of 20 mm diameter. 1L of medium is employed within the flask. the dissolution characteristics are dependent upon the amount of medium pumped through the dissolution chamber. 

35. LANGENBUCHER COLUMN TYPE   This device is according to the dissolution basic design . The screen is constructed such that the medium flows equally through the entire cross section in a laminar pattern. This is again closed by a secondary screen, filter which prevents the undissolved drug from being eluted. 

36. TINGSTAD AND RIEGELMAN a cylindrical glass cell of 6.1 cm long and 1.9 cm in diameter constructed with two glass filter funnels is used. The dissolution cell has filter membranes which prevents the solid particles from being analyzed. There are also external valves to control the excess flow of solvent into the system. the air trap averts air bubbles. The complete assembly is immersed in a temperature bath kept at 37ᵒC

37. MODIFIED COLUMN APPARATUS The device consists of filter of 14 M -size made of nylon. the tubing from the pump is connected to the dissolution cell. the Teflon faced stainless steel supports the screen resting on the bottom half of the filter holder. The direction of the flow is such that the particles do not fall through the screen. the rest of the process is the same. 

38. TAKENAKA The release of drug is measured with the aid of in vitro simulator device consisting of flow type dissolution container. The dosage form is placed in the basket rotating at 94 rpm with 300 ml of medium. then the medium is removed by collecting reservior using peristaltic pump. aliquots are withdrawn using syringe and then filtered using Whatman filter paper and the same volume is replaced immediately with fresh medium.

39. IN VITRO DISSOLUTION AND DRUG RELEASE STUDY INVOLVES : Preparation of solutions for calibration curve Stock solution Sample solution Buffer solution Determination of absorption maxima Preparation of calibration curve Dissolution study Dissolution procedure was carried out. Plot a graph between Time intervals on x-axis vs % of drug release on y-axis. Find out the slope, concentration, amount of drug release, percentage of drug release and report it.

40. DRUG RELEASE TESTING Drug release is the process by which a drug leaves a drug product Drug release : Immediate release (IR) Sustained Release (SR) Sustained Action (SA) Extended Release (ER) Long Acting (LA) Prolong Action (PA) Controlled Release (CR) Timed Release (TR)

41. Immediate release drug products allow drugs to dissolve with no intention of delaying or prolonging dissolution or absorption of the drug Prolonged-release dosage forms Prolonged-release dosage forms are modified-release dosage forms showing a slower release of the active substance(s) than that of a conventional-release dosage form administered by the same route. Delayed release is defined as the release of a drug at a time other than immediately following administration. Enteric Coated: Intended to delay the release of the drug (or drugs) until the dosage form has passed through the stomach. Enteric-coated products are delayed-release dosage forms.

42. Controlled release includes extended-release and pulsatile -release products Extended-release products are formulated to make the drug available over an extended period after administration. Pulsatile release involves the release of finite amounts (or pulses) of drug at distinct time intervals that are programmed into the drug product. Repeat action products contain two single doses of medication; one for immediate release; another one for modified release

43. Targeted release drug release directed toward isolating or concentrating a drug in a body region, tissue or site of absorption or for drug action Drug release and dissolution Modified-release dosage forms include both delayed and extended-release drug productsModified -release dosage forms are preparations where the rate and/or place of release of the active substance(s) is different from that of a conventional- release dosage form administered by the same route.

44. APPARATUS FOR DRUG RELEASE TESTING OF VARIOUS DOSAGE FORMS : DOSAGE FORM EXAMPLE RELEASE METHOD Oral solid dosage forms Basket apparatus, paddle apparatus, reciprocating cylinder, flow through cell Oral suspensions Paddle apparatus Oral disintegrating tablets Padder apparatus, disintegration method Chewable tablets Basket apparatus, paddle apparatus, reciprocating cylinder Powders and granules Flow through cell Thin dissolvable films Basket apparatus, disintegration method Chewing gum Special apparatus Dermal delivery systems(patches) Paddle over disk Topical (semisolid dosage forms) Franz cell diffusion system Suppositories Paddle apparatus, modified basket apparatus Microparticulate formulations Modified flow through cell Implants Modified flow through cell Aerosols Cascade impactor

45. IN VITRO DRUG RELEASE TESTING ROTATING BASKET METHOD : In vitro release study was carried out by the rotating basket method. Six tablets of each batch were taken and placed in rotating basket, respectively. Then the rotating basket was introduced into 900 mL of each dissolution medium (water, 0.1 M HCl and pH 6.8 phosphate buffer) at 37˚C ± 0.5˚C with a rotation speed of 100 rpm. 5 mL of sample solution was collected at different time intervals (2, 4, 6, 8, 10, 12 h) and filtered through a 0.45 µm hydrophilic membrane .

46. 1.0 mL of subsequent filtrate was taken accurately to add into a 100 mL volumetric flask and diluted with the corresponding dissolution medium to 100 mL and mixed well. The amount of drug dissolved in the dissolution medium was measured using an UV-visible spectrophotometer at 233 nm. The same volume of fresh dissolution medium at the same temperature was added to replace the amount withdrawn after each sampling. The drug amount of cumulative release was calculated with a standard curve.

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