Microspheres are characteristically free flowing powders consisting of protiens or synthetic polymers which are biodegradable in nature and ideally having a particle size less than 200 μm. Ideal characteristics of microspheres The ability to incorporate reasonably high concentrations of the drug. Stability of the preparation after synthesis with a clinically acceptable shelf life. Controlled particle size and dispersability in aqueous vehicles for injection. Release of active reagent with a good control over a wide time scale. Biocompatibility with a controllable biodegradability. Susceptibility to chemical modification.
1. Microspheres provide constant and prolonged therapeutic effect.
2. Reduces the dosing frequency and thereby improve the patient compliance.
3. They could be injected into the body due to the spherical shape and smaller size.
4. Better drug utilization will improve the bioavailability and reduce the incidence or intensity of adverse effects.
5. Microsphere morphology allows a controllable variability in degradation and drug release.
Some of the disadvantages were found to be as follows
1. The modified release from the formulations.
2. The release rate of the controlled release dosage form may vary from a variety of factors like food and the rate of transit though gut.
3. Differences in the release rate from one dose to another.
4. Controlled release formulations generally contain a higher drug load and thus any loss of integrity of the release characteristics of the dosage form may lead to potential toxicity.
5. Dosage forms of this kind should not be crushed or chewed.
Microspheres used usually are polymers. They are classified into two types1.Synthetic polymers divided into two types
a. Non-biodegradable polymers
e.g. Poly methyl methacrylate (PMMA), Acrolein, Glycidyl methacrylate, Epoxy polymers.
b. Biodegradable polymers
e.g. Lactides, Glycolides& their co polymers, Poly alkyl cyano acrylates, Poly anhydrides.
2. Natural polymers obtained from different sources like proteins, carbohydrates and chemically
Proteins: Albumin, Gelatin, and Collagen.
Carbohydrates: Agarose, Carrageenan, Chitosan,Starch.
Chemically modified carbohydrates: Poly dextran,Poly starch.