Drug release mechanism and models of release kinetics

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DRUG RELEASE MECHANISMS AND MODELS OF RELEASE KINETICS. Guided by, Mr. Kamlesh J. Wadher Prepared by, Gaurav A. Bhatt Email: gaurav.a.bhatt@gmail.com 09096793437 S.K.B.COLLEGE OF PHARMACY, KAMPTEE, NAGPUR.

Types of drug release mechanism:

Types of drug release mechanism Dissolution controlled system. a) Encapsulation b) Matrix Diffusion controlled system. a) Reservoir b) Matrix Dissolution and Diffusion controlled system.

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Water penetration controlled system. a) Swelling controlled b) osmotically controlled Chemically controlled system. a) Erodible b) drug covalently link to polymer Hydrogel.

Dissolution controlled system.:

Dissolution controlled system. In this system the rate controlling step is dissolution. The drug is embedded in slow dissolving or erodible matrix or by coating with slow dissolving substance. It is of two types a)Encapsulation b)matrix

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a) Encapsulation The drug particle are coated or encapsulated by microencapsulation techniques with slow dissolving materials like cellulose, polyethylene glycol, polymethacrylates, waxes etc. The dissolution rate is depend upon the solubility and thickness of coating.

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b) Matrix It is also called as MONOLITHS. They employ waxes such as beeswax, carnubawax, hydrogenated castor oil which controls drug dissolution by controlling rate of dissolution fluid penetration into matrix by altering porosity of rate. The wax embedded drug is generally prepared by dispersing drug in molten wax and congealing and granulating same.

Diffusion controlled system.:

Diffusion controlled system. Rate limiting step is diffusion of drug through inert water insoluble membrane barrier. There are two types, a) Reservoir b) Matrix

Reservoir diffusion system:

Reservoir diffusion system

Matrix diffusion system:

Matrix diffusion system

Water penetration controlled system.:

Water penetration controlled system. Rate controlling step is penetration of water into the system. It is of 2 types. a) swelling controlled system b) osmotically controlled system

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a) Swelling controlled system. This type of systems are initially dry and when placed in body, absorb water or other fluid and it swells. Swelling increases aq. solvent content within the formulation as well as the polymer mesh size, enabling the drug to diffuse through the swollen network into external environment.

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b) Osmotically controlled system . In this type of systems core i.e. osmotically active drug or combination of osmotically inactive drug + osmogen (Nacl) is enclosed within semi permeable membrane made up of bio compatible polymer like cellulose acetate.

Chemically controlled system.:

Chemically controlled system. These type of systems changes their chemical structure when exposed to biological fluid. In this type, the polymer is degraded as a result of hydrolysis into biologically safe and smaller moieties. It is of 2 types, a) Erodible b) Pendent

a) Erodible system:

a) Erodible system

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b) Pendent chain system. It consist of linear or homo copolymers attached to drug. The drug is release from polymer by hydrolysis or enzymatic degradation of linkage. Zero order release can be achieved and cleavage of linkage is rate limiting step. n-(2-hydroxy propyl) methacrylamide.

Hydrogels :

Hydrogels Hydrogels are water swollen 3-D structure composed of primarily hydrophilic polymers. They are rendered insoluble because of chemical or physical cross links. The physical cross links includes crystallites, entanglements or weak association like H-bonds or vanderwaals forces. These cross links provide the physical integrity and network structure. It provide desirable protection to labile drugs, proteins and peptides.


RELEASE KINETICS The various mathematical models are used to evaluate kinetics and mechanism of drug release. The model that best fits the release data is selected based on correlation coefficient value.

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The models are : Zero order release model First order release model Hixson - Crowell release model Higuchi release model Korsemeyer – Peppas release model

Zero order release model:

Zero order release model The equation is, Q t = Q 0 + k 0 t where, Q 0 = initial amt of drug Q t = cumulative amt of drug release at time t K 0 = constant t = time (hrs) Here, the release rate is independent of its concentration.

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The plot between t(hrs) Qt gives straight line that starts from origin. APPLICATION : Modified release dosage forms like coated form, osmotic systems, transdermal systems etc…

First order release model:

First order release model The equation is, log Q t = log Q 0 + kt/2.303 Where, Q0 = initial concentration Qt = cumulative amt of drug release at time t K = constant t = time (hrs) Here, the release rate is depends on its concentration.

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The plot between Time (hrs) Vs log cumulative % of drug remaining to be release gives straight line. APPLICATION : Water soluble drugs in porous matrix. TIME LOG CUM.%DRUG

Hixson – Crowell release model:

Hixson – Crowell release model The equation is, W 0 1/3 - W t 1/3 = ks t Where, W 0 = initial amt of drug W t = remaining amt of drug ks = constant t = time (hrs)

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The plot of cube root of initial conc. Minus cube root of % remaining VS time. APPLICATION : Used for drug release by dissolution mechanism. TIME CUBE ROOTIFINITIAL-CUBRRR0T %OFREMAINING

Higuchi release model:

Higuchi release model The equation is, Q = ( t D Cs (2C – Cs)) 1/2 Where, D = diffusion coefficient The higuchi model is applicable to drug release by diffusion mechanism.

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APPLICATION : Water soluble drugs and also to low water soluble drugs incorporated to solid/semisolid polymer matrix.

Korsemeyer – Peppas release model:

Korsemeyer – Peppas release model The equation is, F = (M t /M) = k m t n Where, F = fraction of drug release at time t Mt = amt of drug release at time t M = total amt of drug in dosage form K = constant

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‘n’ is estimated from linear regression of log (Mt/M) Vs log t. If n = 0.45 indicates fickian diffusion. 0.45<n<0.89 indicates non fickian diffusion. Non fickian diffusion refers to combination of both diffusion and erosion controlled rate release. APPLICATION : Use to analyze the release of p’ceutical polymeric dosage form. When the release mechanism is not known or when more than one type of release phenomena could be involved.


REFERENCE : Chein Y.W., “Novel Drug Delivery System”, II nd ed., 2005, pg. no.47-54, Marcel Dekker, INC., NewYork . Jain N.K., “Controlled & Novel Drug Delivery”, I st ed., 2004, pg.no . 242-242, CBS Publishers & Distributors, New Delhi. Vyas S.P., Khar R.K., “ Targetted & Controlled Drug Delivery”, I st ed.,2004, pg.no . 425-427, CBS Publishers & Distributors, New Delhi. Wikipedia.net

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