Controled Release Drug Administration

During the last two decades there has been remarkable increase in interest in controlled release drug delivery system. This has been due to various factor viz. the prohibitive cost of developing new drug entities, expiration of existing international patents, discovery of new polymeric materials suitable for prolonging the drug release, and the improvement in therapeutic efficiency and safety achieved by these delivery systems. Now-a-days the technology of controlled release is also being applied to veterinary products.

Modified Release Dosage Forms2:    According to the United States Pharmacopoeia the term 'modified release dosage forms' is used to denote the dosage forms for which the drug release characteristics of time course and/or location are chosen to accomplish therapeutic objectives not offered by the conventional dosage forms. Two types of modified release dosage forms are recognised.

1] Extended release dosage forms:
        It is defined as the one that allows at least a two fold reduction in the dosing frequency as compared to that of conventional dosage form.

2] Delayed release dosage forms:

It is defined as one that releases the drug at a time other than “immediately” after administration.
Rationale of controlled drug delivery 
The basic rationale for controlled drug delivery is to alter the pharmacokinetics and pharmacodynamics of pharmacologically active moieties by using novel drug delivery system or by modifying the molecular structure and /or physiological parameters inherent in a selected route of administration.
Terminology3,4    Different terminologies have been used for the new drug delivery system by different authors.
A] Controlled Action:
In this type of dosage forms it provides a prolonged duration of drug release with predictability and reproducibility of drug release kinetics. In this case, the rate of drug absorption is equal to the rate of drug removal from body.
2] Sustained Action:
    In this type of dosage forms, a sufficient amount of drug is initially made available to the body to cause a desired pharmacological response. The remaining fraction is released periodically and is required to maintain the maximum initial pharmacological activity for some desirable period of time in excess of time expected from usual single dose.
3] Prolonged Action:
    These types of dosage form are designed in such a way that it release the drug over an extended period during which pharmacological response is obtained but does not necessarily maintain the constant blood level.
4] Site specific and receptor release:
It refers to targeting of drug directly to a certain biological location.