Introduction of Parenteral Drug DeIivery System

Oral drug delivery in which the systemic bio availability of a drug is often subjected to variations in gastrointestinal transit and
bio transformation in the liver by "FIRST PASS" metabolism.

Parenteral drug delivery, especially intravenous injection, can gain easy access to the systemic circulation with complete drug absorption and therefore reach the site of drug action Rapidly.

The intravenous, subcutaneous, intramuscular, intraperitoneal, and intrathecal routes are all examples of parenteral routes of drug administration. For a variety of reasons, the most notable being physiological and anatomical constraints, not all of these are useful as routes for controlled drug delivery. Up to the present, efforts in developing controlled release parenteral dosage fortes seem to have concentrated the subcutaneous and intramuscular routes, resulting in such products as aqueous and oil solutions, and implants.
There are currently a number of injectable depot formulation on the market.
•    Penicillin G procaine suspensions
•    Medroxy progesterone acetate suspension
•    Fluphenazine enanthate and decanoate in oil solution
•    Insulin-zinc suspensions
•    ACTH -Zn tannate/geletin preparation

When these formulations are injected into subcutaneous or muscular tissues, A depot is formed at the site of injection which acts as a reservoir for drug. Drug Molecules will be released continuously from the reservoir at a rate determined by the characteristics or each formulation. This continuous release of drug molecules will result in a prolonged drug blood level.

The rate of-drug absorption and hence duration of-therapeutic activities will be determined by,
•    The nature of the vehicle,
•    The physicochemical characteristics of the drug,
•    The interaction of drug with vehicles and tissues/fluid

The duration of action of a regular insulin injection is increased by approximately four times when it is completed with protamine to form the slowly dissolving protamine insulin. Oil solution and aqueous and oil suspension, recent efforts have been made to develop controlled and sustained release parenteral delivery systems via encapsulation, carriers, and magnetic systems. Controlled drug delivery is the phasing of drug administration to the needs of a condition at hand so that an optimal amount of drug is used to cure or control the condition in a minimum time. Research in controlled drug delivery during the past decade has led to increasingly sophisticated means to sustain drug delivery. It has also stimulated greater awareness among to pharmaceutical industry, the regulatory agencies the health care profession, and the public at large of the therapeutic advantages of controlled drug delivery systems.
The majority of these systems are based on synthetic polymers of some sort that differ in the degree in the degree of erodibility, swell ability and sensitivity to the biological environment in which they are placed. 'These polymers have been used to Fabricate sysdrogels for oral and parenteral drug delivery, the osmotic pump for oral drug delivery, and patches for transdermal drug delivery. Clearly, in order to fully utilize the potential of polymers in the broad area of drug delivery, it is necessary to understand their fundamental physical, chemical, and biological properties.

The area of controlled drug delivery is also becoming broader in scope in terms of routes of administration. Traditionally, controlled drug delivery systems were developed primarily for the oral route and, to some extent, for the parenteral route. Recently, there has been an explosion in research on drug delivery via the skin, due primarily to the success of several transdermal devices in sustaining drug delivery to the systemic circulation.

Benefits derived from the parenteral controlled release formulations are primarily the achievement of a relatively constant and substantially sustained therapeutic drug level with a reduction in the frequency of injection.
In other words, the injectable dept formulation was developed with primary of objective of stimulating the intravenous infusion an a more practical basis.