Microspheres

Microspheres are small particles of spherical form with form below 200 μm. The analysis is concerned with the microspheres of its benefits, demerits, forms, planning, results and implementation of process variables. Here, in this article it is one of the novel drug delivery system. It overcame a number of problems regarding other forms of dosage. In order to improve bioavailability, the different types of microspheres are used in various ways to provide greater therapeutic efficacy. The effects of process variables on drug trapping, drug release, and particle size are being investigated. Microspheres are typically free flowing powders consisting of naturally biodegradable synthetic polymers. A microsphere has a drug in the middle of the molecule, where it is contained inside a special polymeric membrane.

The microspheres are also called as micro-particles. To overcome some of the problems of conventional therapy and enhance the therapeutic efficacy of a given drug they are designed. At the target tissue the drug should deliver in an optimal amount in the right period of time with the minimum side effect & maximum therapeutic effect, to get the desired effect. The microspheres received much attention not only for the prolonged release but also for targeting of the anticancer drugs to the tumour. The microsphere are spherical microparticles & are used where predictable & consistent particle surface area is important. . The microspheres has the drug located centrally within the particle where it is encased within the unique polymeric membrane. This review focuses on types, materials used, different methods of preparation, evaluation & applications of microspheres.

Microspheres are free flowing particles ranging from 1-1000u. Microspheres are having wide applications in drug delivery system. They are mainly used for targeted drug delivery of anti-cancer agents, ophthalmic agent and can be used for diagnosis purpose. In this article detail discussion was made on the polymers, preparation methods and applications of microspheres in pharmaceutical dosage form development. General methods of preparation are emulsion techniques, phase separation coacervation techniques, spray drying and spray congealing and solvent extraction, in-situ polymerization etc.  Advantages of microspheres use are targeted drug delivery, optimal therapeutic effects and minimum side effects. Recent trends are floating microspheres, radio immobilization using microspheres. Gastro-retentive floating microspheres are low-density systems that have sufficient buoyancy to float over gastric contents and remain in stomach for prolonged period. The drug is released slowly at desired rate resulting in increased gastric retention with reduced fluctuations in plasma drug concentration.

Micro-particulate systems have already shown their potential as a carrier in delivery of many therapeutic molecules. Due to this potential, such systems are now most preferred over other conventional systems of drug delivery. Micro-carriers (Microspheres) shows features like controlled release, improvement in the residence time and thus enhancing bioavailability of administered drug. Nasal microspheres are now a day’s becoming more popular for delivery of many therapeutic moieties. For building of microparticulate systems polymers from natural and synthetic origins are generally used. Drugs which are not suitable for oral administration due to high first pass effect (i:e presystemic metabolism), instability in gastrointestinal tract can be successfully delivered via nasal route. Systems like mucoadhesive microspheres provide sufficient time for drug to remain in contact with mucosal membrane so as to increase their absorption. This is the basic underlined reason suggests why most of the polar drugs have shown improvement in the bioavaibility when compared with their conventional intranasal formulations. This review mainly focuses on the basic aspects of microspheres as a potential carrier in the drug delivery.

Microsphere is a carrier system for delivery of therapeutic candidate. Nasal microspheres offers significant advantages over other type of drug delivery system. It modulates absorption characteristics of the drug by enhancing drug residence time in the nasal cavity and subsequently may increase bioavailability profile of administered drug. Prior to formulation some physicochemical properties of drug are need to be considered like molecular weight, solubility, pKa and partition coefficient of drug etc. Till date various methods have been adopted for fabrication of nasal microspheres are like spray drying, emulsion crosslinking, Solvent Evaporation etc. Obtained microspheres can characterized for various properties like its morphology, drug content, and zeta potential etc. Present  review mainly focuses on overview of microsphere technology for nasal administration of drug.

The present work was aimed to prepare respirable slow release formulation for isoniazid by spray drying method using hydrophilic carrier, chitosan. The chitosan microspheres were crosslinked with glutaraldehyde to modify release characteristics. Microspheres were prepared and evaluated for % yield, drug loading, moisture content, morphological characteristics, particle size, tapped densities, in vitro drug release, in vitro aerosolization and pharmacokinetic parameters. The scanning electron microscopy revealed that microspheres produced were spherical shaped with slight rough surface. The drug loading efficiency of microspheres showed drug loading efficiency was in the range of 84.44 % to 98.24 %. The in-vitro drug deposition revealed that mass median aerodynamic diameter of crosslinked chitosan microspheres (2.82 µm) was better than the uncrosslinked chitosan microspheres (3.85μm). The complete drug release was seen with uncrosslinked microspheres in two hour while crosslinked chitosan microspheres showed sustained drug release for more than 12 hrs. All the formulation batches showed Carr’s index in the range of 28.7 to 34.3 %. The fine particle fraction for crosslinked chitosan microspheres was found to be 69.1%. Pharmacokinetic differ among the free, crosslinked and uncrosslinked formulations. The crosslinked chitosan microspheres showed sustained drug release lasted for more than 3 days with half life of 31.67 hrs. In vitro and in vivo evaluation studies suggested that chitosan microspheres prepared with spray drying method showed promising aerosol properties having potential to use as sustained drug release formulation for isoniazid as inhalable microparticles. 

  Drug development technologies constituting innovations at the formulation end in the pharmaceutical industry has received a lot of attention in past two decades. Drug delivery as an opportunity to extend product life cycles has indeed proved its place in the market with significant advantages of therapeutic gains as well as commercial success. Carrier technology offers an intelligent approach for drug delivery by coupling the drug to a carrier particle such as microspheres, nanoparticles, liposomes, etc. which modulates the release and absorption characteristics of the drug. Mucoadhesion is a topic of current interest in the design of drug delivery systems. Mucoadhesive microspheres exhibit a prolonged residence time at the site of application or absorption and facilitate an intimate contact with the underlying absorption surface and thus contribute to improved and/or better therapeutic performance of drugs. Hence, uptake and consequently bioavailability of the drug is increased and frequency of dosing reduced with the result that patient compliance is improved. In recent years such Mucoadhesive microspheres have been developed for oral, buccal, nasal, ocular, rectal and vaginal for either systemic or local effects. This review article aims to provide various aspects of mucoadhesion, theories of mucoadhesion and the polymers which will shows the excellent mucoadhesive properties. It also contains a number of available methods of preparation of microspheres and its evaluation including in vitro-wash off test for to determine the mucoadhesive property of prepared microspheres.