Drug delivery system' is a relatively new term used in place of 'dosage form' to describe a system for carrying drug(s). The term emphasizes the complicated nature of delivering drug in an optimal fashion. According to consumer's viewpoint, drug delivery is regarded as a method that ensures a drug arrives at relevant in vivo location with minimal side effects. In a modern era of advanced technology, 'drug delivery' is considered to be the technology associated with converting an NME (new molecular entity) into a medicine. In the past, virtually all the oral delivery systems marketed were what we initially called "conventional immediate release products" that disintegrate within 10 or 15 minutes in the GIT wherein the drug is available for absorption. For some drugs, dissolution may take longer because of the drug or the dosage form properties, but the sustained release is not designed.
The principal drawback of conventional oral dosage forms is uncontrolled delivery , which leads to a number of undesired events. Although conventional oral formulations are still widely used dosage forms, they are enhanced today by many innovations. Innovations in drug delivery, by controlling the rate at which the drug is released, offer substantial clinical advantages, including reduced dosing frequency and improved patient compliance; minimized fluctuations of plasma drug concentrations and maintenance of plasma drug levels within desired range; and potential for reduced adverse effects. The 'spansule' drug delivery system by Smith Kline and French in the early 1950s was considered to be the first oral controlled release drug delivery system. Advances made in controlled drug delivery over the past decades have been significant. The use of drug delivery technologies has emerged as an influential force in recent years, as pharmaceutical companies are poised to reap the rewards of the increasing global market.
Why oral drug delivery? :
Oral drug delivery remains the most user-friendly dosage form. It has the highest degree of patient compliance due to its non-invasive mode of delivery. Novel oral formulation needs to be taken once a day is perceived as "patient-friendly" for compliance. Many drugs for chronic disease conditions are still preferred for oral administration for ease of long-term use. This is illustrated by the fact that oral drugs represent 84% sales of world top 50 drugs (source: IMS health).
The most prescribed 100 drugs in the USA that use oral forms are accounted for 76% market value. The field of oral drug delivery has been driven by the increasing cost of developing NME (approx 1.7 billion dollar), by focusing on the improvement in drug bioavailability and new effective indications and also life cycle management of existing products.
Oral controlled release dosage form:
The oral route of delivery remains the preferred option of the consumers, and hence the pharmaceutical industries. Many delivery opportunities are available using oral route. The major technologies in oral delivery are controlled-release, delayed-release, pulsatile-release, taste-masked, gastro-retentive, orally disintegrating tablets (ODT) and micro-emulsion formulations. The oral drug delivery technologies are in a mature phase, with such technologies now being used routinely by pharmaceutical companies for life cycle management. In 2006 US FDA approved 25 significant dosage forms of existing drugs, out of which 10 belongs to orally administered category. Alza Corporation, founded in 1968, was perhaps one of the earliest, true drug delivery companies. The commercial potential of drug delivery technologies, however, came into the limelight with highly successful products approved in the 1990s, including "Cardizem" and "Losec". These products demonstrated how drug delivery can be used with an existing drug to significantly expand its appeal by improving patient compliance. Cardizem was formulated from a multiple-doses-per-day regimen to a once-a-day pill.
Opportunities ahead: The oral delivery drug market is a US $35 billion industry and expected to grow as much as 16 percent per year up to 2008. Sales of these products are expected to expand faster than total pharmaceutical market, in view of an unprecedented number of innovator block bluster drug molecules (22-24) will lose patent protection in the coming two years.
Conclusions: The principal goal of drug delivery is to develop systems that have useful and intended functions. Oral drug delivery technologies have been providing platform to overcome most of the limitations imposed by GI physiology and chrono-pharmacology. The ideal oral drug delivery systems should ensure compliance with treatment by making delivery as convenient as possible for the patients. Without compliance, therapeutic outcomes are affected and overall health care costs increase. With a better understanding of disease, an escalating NME development cost, and the patients' expectation, there will be continuing demand for innovations in oral drug delivery.
(The author is reader in pharmacy Annamalai University, Tamil Nadu, India)