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1. INTRODUCTION

1.1. Current Status of Drug Delivery Systems

During the past two decades, Drug development technology in Pharmaceutical Industry with innovations in formulation development have received a lot of attention. 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. In India drug development technology is still in nascent stage with academia and research institutes collaboration as main stay of the development of novel products. The main motto of Indian companies, in the development of newer pharmaceutical formulations by using NCE in order to achieve by providing cost effective, therapeutically effective with short term and long term options. While development in the oral route is still the main focus, pulmonary, cutaneous, transdermal and other multiple routes are gaining increased attention¹.

The application of modern technology in the field of drugs administered via oral, parenteral, pulmonary and intra-ocular finds a newer, better than the conventional dosage forms is an important era in the drug delivery. The health scenario in India demands Novel Drug Delivery Systems (NDDS) for more than 20 diseases and conditions for which rationale for such system is established. More than half of these conditions are prevalent in India and other developing and under-developing countries only and offer a great challenge and opportunity for the Indian Pharmaceutical Industry².

A number of drug delivery platform technologies currently exist that may be adapted to various drug molecules to yield superior medicines. Such medicines while offering obvious benefits to patients will also generate a more stable and patent protected revenue stream³.

Although the drug delivery concept is not new, a great progress has recently been done in the treatment of variety of diseases. Targeting delivery of the drugs to the lesions and controlling the release rate at the site of action is the most important aspect of Drug Delivery System. Research is being carried out throughout the world at a great place, devising strategies for drug delivery to overcome biological barriers and the physiochemical properties of the modern drugs. Above all the prominence of drug delivery systems can be understood by the variety that out of the $250 billion worldwide value of pharmaceuticals, 10% is attributed to it⁴.

In this context controlled drug delivery along with targeted drug delivery forms the essence of modern and future drug delivery systems.

1.2. Controlled Drug Delivery Systems

As the name implies, CDDS serves two functions. First it involves transport of the drug to particular part of the body and the second function is that of the controlled release.

The main advantages of Controlled drug delivery systems are:

• Maintenance of optimum therapeutic drug concentration in the blood with minimum fluctuations.
• Predictable and reproducible delivery for extended duration.
• Enhancement of activation duration for short half – life drugs.
• Minimizes the side effects.
• Reduce the frequent dosing.
• Reduce the wastage of drug.
• Better patient compliance.

1.2.1. Oral Controlled drug Delivery Systems

Oral controlled release technology was evolved with matrix technology. Several research papers in the 1950s and 1960s reported as simple matrix tablets or monolithic granules. In 1952, a new formulation “spansule” a timed- release formulation was introduced by Smith Kline & French which launched a widespread search for other applications in the design of dosage forms. Advances in oral controlled release technology are attributed to the development of novel biocompatible polymers and machineries that allow preparation of novel design dosage forms in a reproducible manner⁵. For controlled release systems, the oral route has by far received most attention and success because of the fact that gastro-intestinal physiology offers more flexibility in dosage form design than other routes⁶. Apart from that owing to patient acceptance, convenience of administration, cost-effective manufacturing, and generally long product shelf-life is a continuous emphasis to develop oral formulations will persist. Some of the marketed oral controlled release products were listed in table no.1.1.

Table No. 1.1. Marketed oral controlled release products7

1.2.2. Particulate Oral Drug Delivery System

In any drug delivery system the use of carriers to convey a certain dose of the drug is important as drug itself. Various carrier systems in application till date are macromolecular drug carriers, micellar systems, liposomes, red cells and microparticulates. These were used to carry a wide variety of pharmaceutical agents in a number of different therapeutic situations. Among these chiefly microparticulate carriers has been accounted for an important potential application in the administration of therapeutic molecules such as sustained drug delivery in cancer and infectious disease or for the administration of gut labile drugs⁸.

Moreover, due to their size microparticulates are not usually administered through intravenous routes but via alternate routes. Thus, inclusion of drugs in microparticulate carriers clearly holds significant promise for the improvement in the therapy of several disease categories.

They serve many purposes⁹ such as:

• Protecting the incorporated components from degradation
• Controlling drug release
• Increasing adjuvancy
• Targeting to the specific sites.

Due to the unique physiological conditions in the GI tract, the particulate systems are required to meet the following criteria before they can be used as effective oral delivery vehicles¹⁰.

• Firstly they should be resistant to undergo degradation in GI tract.
• The encapsulated drug in the particles need to be absorbed with high efficiency in GI tract to be therapeutically effective. Currently it is believed that, less than 1% of the particles can be absorbed after oral administration.

1.3. Biodegradable polymers and Mucoadhesion

Mucoadhesive polymers

Mucoadhesive polymers¹¹ have properties to get adhered to the mucus membrane and hence capable of prolonging the contact time of the drug with a body tissue. The use of mucoadhesive polymers can significantly improve the performance of many drugs. This improvement ranges from better treatment of local pathologies to improved bioavailability and controlled release to enhance patient compliance.

Ideal characteristics of mucoadhesive polymers¹²

• It should be able to accommodate both oil and water soluble drugs for the purpose of controlled drug delivery.
• It should possess an optimum molecular weight to the mucoadhesive.
• It should demonstrate local enzyme inhibition and penetration enhancement properties.
• It should show specificity for attachment to an area or cellular site.
• It should show specificity and stimulate endocytosis.
• It should be inert and compatible with the environment.
• It should be easy and inexpensive to fabricate.
• It should have good mechanical strength.
• It should possess a wide margin of safety both locally and systemically.

Microspheres can be defined as solid, approximately spherical particles ranging in size from 1 to 1000 μm. They are made of polymeric, waxy or other protective materials, i.e. biodegradable synthetic polymers and modified natural products such as starches, gums, proteins, fats and waxes. Microspheres are small and have large surface to volume ratio. At the lower end of their size range they have colloidal properties. The interfacial properties of microspheres are extremely important, often dictating their activity.

Microparticles are of two types

1. Microcapsules: The entrapped substance is completely surrounded by a distinct capsule wall.
2. Microspheres: The entrapped substance is dispersed throughout the microsphere matrix are shown in the Fig: 1.1.

Fig: 1.1. Differentiation between microcapsules and microspheres

Microsphere carrier systems made from the naturally occurring biodegradable polymers have attracted considerable attention for several years in sustained drug delivery. However, due to short residence time at the site of absorption, the success of these microspheres is limited. By providing the drug delivery system a means of intimate contact with the absorbing membrane, these delivery systems would be advantageous which can be achieved by coupling mucoadhesion characteristics to microspheres and developing mucoadhesive microspheres^13,14.