DISSOLUTION

DISSOLUTION: 

DISSOLUTION Presented By: Shilpi Bhatnagar M.Pharm (Q.A.) Gyan Vihar School Of Pharmacy

CONTENTS: 

CONTENTS INTRODUCTION GOALS OF DISSOLUTION TEST IDEAL FEATURE OF DISSOLUTION APPARATUS TYPES OF DISSOLUTION APPARATUS APPARATUS USED FOR NOVEL/SPECIAL DOSAGE FORM CONCLUSION REFERENCES

INTRODUCTION: 

INTRODUCTION It is a process by which drug released from solid dosage form and immediately goes into molecular solution. Dissolution is defined as process by which a known amount of drug substance goes into solution per unit of time under standardized conditions. Dissolution is principally useful as a QC test. It can be predictive of in vivo behavior, but this must be demonstrated by an in-vivo in-vitro correlation study (IVIVC).

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The absorption of solid drugs administered orally can be depicted by the following flowchart: where K d & K a are rate constants for the dissolution & absorption respectively. When dissolution is the significantly slower of the two processes (i.e., k d « k a ) the absorption is described as dissolution rate-limited. A ny change in the process of dissolution would influence the absorption. K d Dissolution K a Absorption

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A. Intrinsic Dissolution Rate: The dissolution rate of a solid in its own solution is adequately described by the Noyes-Nernst equation: dc = AD (Cs – C) dt hV ……eq. (1) where dC / dt = dissolution rate A = surface area of the dissolving solid D = diffusion coefficient C = solute concentration in the bulk medium h = diffusion layer thickness V = volume of the dissolution medium Cs = solute concentration in the diffusion layer

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During the early phase of dissolution, Cs » C and is essentially equal to saturation solubility S. Surface area A and volume V can be held constant. Under these conditions and at constant temperature and agitation, Equation (1) reduces to dC = KS dt ….eq(2) where K = AD/hV = constant. Dissolution rate as expressed in Equation (2) is termed the intrinsic dissolution rate (IDR) and is characteristic of each solid compound in a given solvent under fixed hydrodynamic conditions. The intrinsic dissolution rate in a fixed volume of solvent is generally expressed as mg dissolved x (min -1 cm -2 ).

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B. Common Ion Effect: A common interaction with solvent, which is often overlooked, is the common ion effect. The addition of a common ion often reduces the solubility of a slightly soluble electrolyte. To identify a common ion interaction, the IDR of the hydrochloride salt should be compared between: Water & water containing 1.2% w/v NaCl, 0.05 M HCl & 0.9% w/v NaCl in 0.05 M HCl.

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C. Particulate Dissolution: Particulate dissolution is another method of studying the dissolution of solids. A weighed amount of powder sample from a particular sieve fraction is introduced in the dissolution medium. Agitation is usually provided by a constant-speed propeller. Particulate dissolution is used to study the influence on dissolution of particle size, surface area, and mixing with excipients.

Means of enhancing slow dissolution: 

Means of enhancing slow dissolution In absence of more soluble physical or chemical form of the drug - Particle size reduction (most commonly used). Enhanced surface area by adsorbing the drug on an inert excipient with a high surface area, i.e., fumed silicon dioxide. Co-precipitating, or triturating the drug with some excipients. Incorporation of suitable surfactant.

Goals of Dissolution test : 

Goals of Dissolution test To accessing therapeutic efficacy. Monitoring batch to batch consistency. Assessment of bioequivalence. Requirement for regulatory approval for product marketing and is a vital component of the quality control program.

THE IDEAL FEATURES OF A DISSOLUTION APPARATUS : 

THE IDEAL FEATURES OF A DISSOLUTION APPARATUS Must be simply designed. Must be enough sensitive. Uniform hydrodynamic flow is essential. An easy means of introducing dosage form. Provide minimum mechanical abrasion to the dosage form. The medium must be maintained at a fixed temperature. Samples should be easily withdrawn.

Types of dissolution apparatus : 

Types of dissolution apparatus USP dissolution apparatus (official): Apparatus 1:Basket type (37ºc) Apparatus 2: Paddle type (37ºc) Apparatus 3: Reciprocating cylinder(37ºc) Apparatus 4: Flow through cell (37ºc) Apparatus 5: Paddle over disc (32ºc) Apparatus 6: Rotating cylinder (32ºc) Apparatus 7: Reciprocating disc

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USP dissolution apparatus ( non- official): Rotating bottle method Diffusion cell Peristalsis method Intrinsic dissolution method

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IP dissolution apparatus: Apparatus 1: paddle type Apparatus 2: Basket type BP dissolution apparatus: Apparatus 1: basket type Apparatus 2: paddle type Apparatus 3: flow through cell

USP Apparatus 1: Basket type: 

USP Apparatus 1: Basket type

USP Apparatus 2: Paddle type: 

USP Apparatus 2: Paddle type

Apparatus used for novel/special dosage form : 

Apparatus used for novel/special dosage form Types of dosage form Release method Solid oral dosage forms(conventional) Oral suspension Orally disintegrating tablets Chewable tablets Transdermal-patches Suppositories Basket,paddle,reciprocating cylinder, or flow through cell Paddle Paddle Basket, paddle,reciprocating cylinder Paddle over disk Paddle, modified basket, or dual chamber flow through cell

CONCLUSION: 

CONCLUSION An appropriate drug release test is required to characterize the drug product and ensure batch-to-batch reproducibility and consistent pharmacological or biological activity. Dissolution test continues to increase in importance as a quality control test in pharmaceutical analysis and drug development. These methods are also designed to mimic the physiological environment of the GIT and have increased the likelihood of establishing in vitro – in vivo correlation. The in vitro drug release test for some novel/special dosage forms such as semisolid dosage forms and transdermal drug delivery systems has proven to be as valuable as the dissolution test for solid oral dosage forms.

REFERENCES: 

REFERENCES Wells J.I and M.E Aulton, The Drug Delivery System, p. 234-235 Martin Alfred, Physical Pharmacy, 4 th edition, p.330-332 William. L and Wilkins. Remington, The science and practice of pharmacy, 21st ed., Vol 1. p. 672-88 Brahmankar. D.M , Sunil B. Jaiswal. Biopharmaceutics and Pharmacokinetics A Treatise 5th ed. P. 19-49 www.authorstream.com

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