APPROACHES FOR THE DEVELOPMENT OF IMPLANTABLE DRUG DELIVERY SYSTEMS:

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Hi bloggers

A warm wishes to all.

Here comes my second blog about the various approaches for implantable drug delivery systems, formulations and fabrications.

I wish everyone go through my last blog (http://www.pharmainfo.net/satyajeethpandey/blog/implantable-therapeutic-systems-i) to have a better understanding.

1.CONTROLLED DRUG DELIVERY BY THE PROCESS OF DIFFUSION:

A. A polymer membrane permeation,controlled drug delivery using non porous or micro porous or semi permeable membrane.

B.matrix diffusion controlled delivery using lipophilic or hydrophilic or porous polymers.

C.micro reservoir partition controlled drug delivery using hydrophilic reservoir in lipophilic matrix and vice versa

D.membrane
matrix hybrid drug delivery using lipophilic membrane with hydrophilic matrix and vice versa

2.CONTROLLED DRUG DELIVERY BY ACTIVATION PROCESS:

A.osmotic pressure activated drug delivery system

B.vapor pressure activated drug delivery system.

C.magnetically activated drug delivery system.

D.phonophoresis activated drug delivery system.

E.hydration activated drug delivery system.

F.hydrolysis activated drug delivery system.

3.CONTROLLED DRUG DELIVERY BY FEED BACK REGULATED PROCESS:

A.bioerosion regulated drug delivery

B.bio responsive drug delivery

1. CONTROLLED DRUG DELIVERY BY DIFFUSION PROCESS:

a.polymer membrane permeation controlled drug delivery using non porous or micro porous or semi permeable membrane:

in this drug reservoir is encapsulated within a capsule shaped or spherical compartment that is totally enclosed by a rate controlling polymeric membrane.

Drug present may be solid particles or a dispersion of drug particle in liquid or solid

The polymeric membrane may be non porous or micro porous or semipermeable

The subcutaneous release of levonogestrel from Norplant implant in human female is constant over a duration of more than 6 years.

here drug dipersion is formed by homogenous dispersion of drug solid particles throughout a lipophilic or hydrophilic polymer matrix.

The dipersion is done by blending solids with viscous liquids or semisolid polymers at room temperature and the melting and crosslinking at elevated temperature.The drug polymer dispersion is moulded or extruded from the device.

Microspheres are also made by coacervation and solvent evaporation method and designed as implant pellet.

e.g..subcutaneous release of estradiol from implants tested in rats

C.micro reservoir partition controlled drug delivery using hydrophilic reservoir using hydrophilic reservoir in lipophilic matrix and vice versa

Here drug reservoir contains micro dispersions made by suspension of drug crystals in aqueous solutions of polymer utilizing high energy dispersion technique.

This result a homogenous dispersions of millions of discrete
unleachable,microscopic,drug reservoirs in polymer matrix

These micro dispersions are then used to make pellets by moulding or extrusion

d. membrane matrix hybrid drug delivery using lipophilic membrane with hydrophilic matrix and vice versa

This is a hybrid of membrane permeation and matrix diffusion system

Here constant drug release kinetics is maintained by membrane permeation system with minimum risk of dose dumping.

A drug reservoir is made by polymeric matrix formation which is further encapsulated by polymeric membrane for rate controlling.

2.CONTROLLED DUG DELIVERY BY ACTIVATION PROCESS

a.osmotic pressure activated drug delivery system

in this device osmotic pressure is used as energy source to activate and modulate drug delivery

drug reservoir (a solution or a semisolid formulation)is contained within a semi permeable housing with controlled water permeability .After activation solution is released.

The rate of release occurs as

Dv/dt=PwAm/hm[sigma(pis-pie)-(Ps-Pe)]

Pw=water
permeability

Am=effective
surface area

Hm=thickness
of semipermeable membrane

Sigma=reflection coefficient of membrane

(pis-pie)=differential osmotic pressure between delivery system and environment

(Ps-Pe)=differential hydrostatic pressure between delivery system and environment

e.g:ALZET OSMOTIC PUMP

B.vapour pressure activated drug delivery system:

Vapour pressure is used as the power source to activate the controlled delivery of drugs.

Drug solution is put in an infusate chamber which is separated from the vapour pressure chamber by movable bellows.

Vapour pressure chamber contains a vaporizable fluid (fluorocarbon).it vapourizes at body temperature,increases the pressure,pushes the bellow and thus solution comes out through the floe regulators and cannulas in blood circulation at constant flow rate.

C.magnetically activated drug delivery system

Electro magnetic energy is used as the power source to activate the delivery of drugs and to control the rate of drug delivery

A magnetic wave triggered mechanism is incorporated into the device which controls the release rate.A zero order drug release profile was achieved.

The system contains a magnet inside the reservoir.By applying the external magnetic field,drugs are activated by electromagnetic energy and then released.

D.hydration activated drug delivery system

Release of drug molecules is upon activation by hydration of the device tissue fluid at the implantation site.

Hydrophilic polymer used in this system is swollen upon by hydration and molecules are released upon diffusion.

The device is fabricated by polymerzing ethylene glycol methacrylate in an alcoholic solution containing the drug,a cross linking agent(ethylene
dimethacrylate)and an oxidizing catalyst to form cylindrical vials swellable implant.

E.hydrolysis activated drug delivery system:

Activation is done by hydrolysis of polymer base by tissue fluid at the implantation site

Polymer used in making drug matrix is bioerodable or biodegradable through hydrolysis.the drug diffusion occurs from matrix.

polymers used are poly(lactide-glycolide) copolymer, polysaccharide. polypeptide,polyanhydride.

Reference:

Novel drug delivery systems by yie w.chien, 2nd edition, volume 50, Marcel and Dekker Publishers, page no 443 to 458.

"This blog does not contain plagiarized material"

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