dissolution

Views:
 
Category: Education
     
 

Presentation Description

dissolution,AIMST

Comments

Presentation Transcript

PowerPoint Presentation:

DISSOLUTION Definition: mass transfer from solid surface to the liquid phase or solid substance in a given solvent. Drug released from solid dosage forms Immediately go into molecular soln. Process is called dissolution-after dissolution –absorption is possible

PowerPoint Presentation:

Amount of solid substance goes into solution per unit time under standard Condition Temp pH solvent composition and solid surface area is called Dissolution rate

PowerPoint Presentation:

Low aqueous drug solubility. Poor product dissolution – evidence from the literature that the dissolution of one or more marketed products is poor. Drug particle size – evidence that particle size may affect bioavailability. The physical form of drug – when polymorphs, solvates and complexes have poor dissolution characteristics. Presence of specific excipients which may alter dissolution or absorption. Tablet or capsule coating which may interfere with the disintegration or dissolution of the formulation. The physicochemical factors which point to the need for dissolution testing include:

PowerPoint Presentation:

Diffusion layer model/film theory Solid surface Solid/liquid interface Stagnant layer of thickness h and concentration c s Diffusion of molecule Bulk of the solution With conc . c b Dissolving solid drug GI Lumen GI Barrier blood Theory of dissolution

PowerPoint Presentation:

Around the drug particle a thin film (or) layer are formed-called as the Stagnant film or diffusion layer which is saturated with the drug-this Step usually rapid . Diffusion of the soluble drug from the stagnant layer to the bulk of the Solution ; This step is slower (rate determine step) Noyes and Whitney dc dt = K (C S - C b ) eqn 1 dc dt - Dissolution rate of drug K - dissolution rate constant C S - Conc. of drug in the stagnant layer C b - conc. of drug in the bulk of soln at time t eqn 1 -according to ficks second law Diffusion layer model/film theory

PowerPoint Presentation:

Nernst and brunner incorporated ficks first law Modified noyes and whitneys eqn………….. dt DAK w/o (C S – C b ) vh dc = D- Diffusion coefficient A-Surface area of the dissolving solid V-Volume of dissolution medium H-Thickness of stagnant layer More value More dissolution Se viscosity of medium Se dissolution More surface area More disso. More thickness Less disso. w/o – water/oil partition coefficient Higher value More disso. (C S – C b )-Conc. Of gradient for diffusion of drug

PowerPoint Presentation:

= K ….under sink condition-zero order ….under non sink condition-first order According to Noyes and Whitney dc dt Surface area of dissolving particle same throughout experiment Practically not possible (particle size decrease, change in surface area) Hixson and Crowell's cubic root law

PowerPoint Presentation:

Hixson and Crowell's cubic root law W 0 1/3 - W 1/3 =Kt W 0 W K - Original mass of drug -mass of the drug remaining to dissolve at time t -dissolution rate constant Dankwert’s didn’t approve stagnant theory and suggested

PowerPoint Presentation:

When agitation is consider (small solvent packets are generated) Small packets solvent rotate random motion Empty solvent packet approach with solid drug surface Carry the drug Diffusion take place Packets are replaced by empty pockets of fresh solvent Since the solvent packets are exposed to new solid surface each time is called surface renewal theory

PowerPoint Presentation:

Dissolving solid Dankwert’s model (penetration or surface renewal theory) S/L interface having Conc. Cs Fresh packet of solvent Approaching the interface Packet of solvent saturated With Drug leaving the interface Bulk of the soln having Conc. C b dc dm γ D dt dt V = = (C S – C b ). M-mass of solid dissolved γ - rate of surface renewal or the interfacial tension

PowerPoint Presentation:

Dissolution test is specified for its compliance in the individual monograph, particularly for tablets and capsules. Dissolution methods official in the USP Apparatus 1 – Rotating basket type : Used for testing of drugs having appreciable aqueous solubility. In this type, agitation is not vigorous . A few examples of drugs that are tested by this type are: Lithium carbonate tablets USP Phenylbutazone tablets USP Extended phenytoin sodium capsules USP Basket method is a widely used procedure. Apparatus consists of following parts

PowerPoint Presentation:

A . Cylindrical vessel : Normally it is made of glass or other transparent material. It may be flat bottomed or spherical bottomed and contains a flanged lid. Its capacity is 1000 ml. B. Variable speed motor : The speed of the motor should be capable of being varied between 25 to 150 rpm and maintained with in 5% required speed. A basket is attached to the shaft of the motor C. Basket : A cylindrical stainless steel basket assembly is made of woven wire cloth with a nominal aperture size of 425 μ m. Joined down one side with a narrow welded seem. Gold coating is required for acidic media. The top of the basket is attached to the disc of the driving shaft by three clips. The dosage form under test is placed in the basket and allowed to rotate by motor

PowerPoint Presentation:

D. Withdrawal port : This facility is used to withdraw sample of dissolution medium from point approximately half-way between the basket wall and wall of the vessel, and halfway between the surface of dissolution medium and bottom of the vessel. E. Water bath : The cylindrical vessel is securely clamped in a water bath. It is set to maintain the temperature of the dissolution medium in the vessel at 37 ± 0.5 0 C. Apparatus type 2- Hansen Paddle type (USP) Prescribed for poorly water soluble drugs. The method provides more vigorous conditions to yield quick results. Examples: Tolbutamide tablets USP Methaqualone tablet USP An assembly can be described as:

PowerPoint Presentation:

The assembly is same as apparatus 1, except that a shaft carrying paddle is used as the stirring element. The shaft is suitably positioned and rotate smoothly. The metallic blade and shaft comprise a single entity that may be coated with a suitable fluorocarbon polymer. The dosage unit is allowed to sink to the bottom of the vessel before rotation of the paddle is started. A small, loose piece of non reacting material such as wire or glass helix may be attached to dosage unit to avoid floating.

authorStream Live Help