Controlled Drug Delivery System: Definition / Terminologies and Rationale.

As we have seen oral drug delivery although very popular has certain drawbacks.
To imagine an ideal drug delivery following important points should be taken into the consideration,

It should be a single dose for the duration of treatment.
It should deliver the active drug directly to the site of action, thereby minimizing or removing side effects.

Controlled drug delivery is one which delivers the drug at a predetermined rate, locally or systemically, for a specified period of time.
However it is observed that many terms are used synonymously, to differentiate them from one another we are going to discuss different terminologies that are used in NDDS related to controlled release formulations.

Different terms used in novel drug delivery systems,

A dosage form that releases a separate fraction of the drug at a time or times other than administration, although one portion may be released immediately after administration.
e.g. ; enteric-coated tablets, where a timed-release is achieved by barrier coating repeated action tablets or spansules.

When absorption of the drug is greater than its elimination, the release is known as extended-release.
A dosage form should allow at least a two fold reduction in dosage frequency as compared to that drug presented as an immediate release dosage form.
These include; any dosage form that maintains the therapeutic blood or tissue level of the drug for a prolonged period of time.

It includes the drug delivery systems that achieve and ensure a slow release of drugs over an extended/prolonged period or at a constant release rate to attain and maintain therapeutically effective levels of drug concentration in the circulation.
Here the absorption rate is equal to the elimination rate over an extended period.

It includes any drug delivery system by which the drug is delivered at a predetermined rate over a prolonged period.

It is a dosage form that releases drugs at or near the intended physiologic site of action.
Targeted release dosage forms may have either immediate or extended-release characteristics.
They usually contain suitable site directing molecules, which recognize their receptor or molecular attachment sites at the target.

In this type of system, the target is a particular receptor within an organ or tissue.

Also called Flash release systems.
It is a type of solid dosage form that dissolves or disintegrates in the oral cavity without the help of water or chewing.
Fast dissolution is achieved by forming,
a loose network, or by effervescent agent, or with a mixture of disintegrating agents.

The basic rationale of controlled drug delivery is to change the pharmacokinetics and pharmacodynamics of drugs by using NDDS or by modifying the molecular structure and/or physiological parameters inherent in a selected route of administration.
The primary objectives of controlled drug delivery are to ensure safety and to improve the efficacy of drugs as well as patient compliance.
For conventional dosage forms, only the dose and dosing interval can vary and for each drug, there exists a therapeutic window of plasma concentration below which therapeutic effect is insufficient and above which undesirable or toxic side effects are elicited.
This is often defined as, “the ratio of median lethal dose (LD50) to median effective dose (ED50)”.