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Microsphere: An Overview
5.1) For biodegradable: -
5.1.1) Degradation controlled monolith system:-
In degradation controlled monolithic microspheres system, the drug is dissolved in the matrix is in degradation controlled monolithic microspheres system, the dissolved and is released only on degradation of the matrix. The diffusion of the drug is slow compared with the degradation of the matrix. When degradation as by homogeneous bulk mechanism, drug release is show initially and increase rapidly when repaid bulk degradation starts. Drug release from such type of device in independent of the geometry of the device if the degradation is by homogeneous mechanism, degradation is confined to the surface. Hence rate of release is affected by the geometry of the device.
5.1.2) Diffusion controlled monolith system:-
Here the active is released by diffusion prior to or concurrent with the degradation of the polymer matrix. Degeneration of the polymer matrix affects the rate of release and to be taker into account. Rate of release also depends on whether the polymer degrades by homogeneous or heterogeneous mechanism.
5.1.3) Erodable polyagent system:-
In this case the active agent is chemically attach to matrix & the rate of biodegradation of matrix is slow compared to the rate of hydrolysis of drug-polymer bond. Assuming that the rate of diffusion of active agent from the matrix to the surrounding is rapid, the rate limiting step is the rate of cleavage of bond attaching drug to polymer matrix. This type of delivery is obtained in the release of norethindrone-17-chlorofirmate which is then attached to the –OH group of polymer. In vitro studies in rats using labeled drug polymer conjugate showed that a fairly constant release is obtained during the time of observation which was 5 months
5.2) Utilization of Microspheres in Body
Microparticulate carrier system can be administered through different routes such as i.v,ocular,i.m,oral,intra arterial.etc.Each routes has it’s own biological significance, limitation & pharmaceutical feasibility. The micro particles are intended to be administration through differents routes to achieve desired activity of either sustained action or targeting or both.Throgh different routes different mechanisms of uptake,transport & fate of translocated particles have been proposed.
Biodegradable microparticulate carriers are of interest for oral delivery of drugs to improve bioavailability, to enhance drug absorption,to target particular organ 7 to reduce toxicity to improve gastric tolerance of gastric irritant to stomach & as a carrier for antigen. The polystyrene microspheres administered orally are reported to be taken up by Peyer’s Patch. They are subsequently translocated to discrete anatomical compartments such as mecentric lymph vessels,lymh nodes & to a lesser extent in liver & spleen. The particulates matters gain entry into follicle associated epithelium through Peyer`s patches.
After the uptake of particulate carriers via different mechanism their fate become more important. Some uptake mechanism avoids the lysosomal system of the enterocytes.The particles following uptake by enterocytes are transported to the mecentric lymph, followed by systemic circulation & subsecuently phagocyosized by the Kupffer cells of liver.However,after uptake by enterocytes,some particulate carriers may be taken up into vacuoles & discharged back into gut lumen.
Microsperes can also be designed for the controlled release to the gastrointestinal tract. The release of drug contents depends on the size of micro particles & the drug content within microspheres.The release of the drug could be regulated by selecting an appropriate hydrophilic/lipophilic balance of the matrix such as in case of matrix of polyglycerol,ester of fatty acids.Microparticles of mucoadhesives polymers get attached to the mucous layer in GIT & hence, prolong the gastric residence time & functionally offer a sustained release. The microspheres of particle size less then 0.87 µm are taken to the general circulation. The fluid environment of the GIT can affect the number & rate of particles translocation.
6) Application of Microspheres
6.1) In enteric release dosage form.
Drugs which are irritant to the stomach & other side effects like aspirin, pancrelipase & erythromycin, salbutamol sulphate can be incorporated in microspheres for their selective release in intestine.
6.2) To protect reactive materials against environment.
It is useful for drugs vitamins. Aspirin which aresensitiveto oxygen & water.
6.3) To mask bitter of unpleasant taste of the drug
E.g. for drugs such as quinidine, nitrofurantion, paracitamol prednisolone, metronidazole, fish oils, sulpha drugs, clofibrate, alkaloids & salts.
6.4) For drug targeting.
E.g. casein & gelatin microspheres containing Adriamycin & iterferons respectively were magnetically delivered to tumour site. Albumin microspheres used for anti-inflammatory agents for directing against knee joints.
6.5) As a topical drug delivery system.
E.g.Microspheres of benzoyl peroxide for their bactericiday activity against acne.
6.6) As an antidote in the poisoning of heavy metals.
E.g Polymercaptal microspheres as an antidote against mercury poisoning.
6.7) As antigen carrier.
E.g. & PLGA microspheres of varying composition have used to improve the ability of the antigens to provoke a mucosal immune response.
6.8) To reduce gastric irritation.
Hard gelatin capsule containing microspheres liberate in stomach & spread in the overall GIT, thus ensuring more reproducible drug absorption with less local irritation
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