II. required, lower effectiveness, toxicity and adverse side effects.



The  oral 
route  of  drug 
administration  is  the 
most  important  method 
of  administering  drugs 
for systemic effects. The parenteral route is not routinely used for
self administration of medication. The topical route of administration has only
recently been employed to deliver drugs to the body for systemic effects. It is
probable that at least 90 % of all drugs used to produce systemic effects
are  administered  by 
the  oral  route. 
When  a  new 
drug  is  discovered, 
one of  the  first 
questions  a pharmaceutical  company asks 
is whether or not the drug can  be
effectively  administered  for 
its intended effect by the oral route. If it cannot, the drug is
primarily relegated to administration in a 
hospital  setting  or 
physician’s  office.  Solid 
oral  dosage  forms 
represent  the  preferred 
class  of product. The reasons for

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this preference are well known.

Conventional drug delivery involves the formulation of the drug into a
suitable form, such as a compressed tablet for oral administration or a
solution for intravenous administration. These dosage forms have been found to
have serious limitations in terms of higher dosage required, lower
effectiveness, toxicity and adverse side effects. New drug delivery systems
have been developed or are being developed to overcome the limitation of the
conventional drug delivery systems to meet the need of the healthcare


Problems of Traditional Drug

An ideal dosage regimen in the
drug therapy of any disease is one which immediately attain the desired
therapeutic concentration of drug in plasma and maintains it’s constant for the
entire duration of treatment. This is possible through the administration of
conventional dosage forms in a particular dose and at particular frequency. The
frequency of administration or dose interval of any drugs depends upon its half
life or mean residence time and its therapeutic index.

In most cases, dosing interval is
much shorter than the half life of the drug, resulting in number of limitations
associated with such a conventional dosage form which is

Poor patient
compliance; increased chances of missing the dose of a drug with short half
life for which frequent administration is necessary.

A typical peak
valley plasma concentration time profile is obtained which makes attainment of
steady state condition difficult.

The unavoidable
fluctuation in the concentration may lead to under medication or over
medication as the C ss value fall or rise beyond the therapeutic range.

The fluctuating drug level may
lead to precipitation of adverse effect especially of a drug with

small therapeutic index whenever
over medication occurs.


Need for New Approach of Drug
Delivery System

To overcome the problem that we
mention before, it clearly indicates that the need of the development of the
non traditional dosage forms.

There are 2 ways to overcome such

Development of
new, better and safer drugs with long half life and large therapeutic indices.

Effective and
safer use of existing drugs through concepts and techniques of sustained/
controlled and targeted drug delivery systems.

Oral controlled/sustained release
dosage forms are being developed since past three decades due to their advantages.
The design of oral controlled/sustained release drug delivery systems should
primarily be aimed at achieving more predictable and increased bioavailability
of drugs.








The oral form of drug delivery
system is considered the most preferred an patient convenient means of drug
administration. While significant advances have been made in the development of
elegant systems to modify the oral delivery of drugs, the basic approaches have


The drugs have an optimum concentration range within which maximum benefit
is derived, and concentrations above or below this range can be toxic or
produce no therapeutic benefit at all 1. On the other
hand, the very slow progress in the efficacy of the treatment of severe
diseases, has suggested a growing need for a multidisciplinary approach to the
delivery of therapeutics to targets in tissues.

From this, new ideas on controlling the pharmacokinetics, pharmacodynamics,
non-specific toxicity, immunogenicity, and efficacy of drugs were generated.
These new strategies, often called drug delivery systems (DDS), which are based
on interdisciplinary approaches that combine polymer science, pharmaceutics,
chemistry, and molecular biology. To minimize drug degradation and loss, to
prevent harmful side-effects and to increase drug bioavailability and the
fraction of the drug accumulated in the required zone, various drug delivery
and drug targeting systems are currently under development 1. During the last decade and half pharmaceutical and
other scientists have carried out an intensive investigations in this field of
drug research.

Modified release formulation
technologies offer an effective means to optimize the bioavailability and
resulting blood concentration time profile of drugs. Modified release

dosage forms are those
preparations where the rate and/ or place of release of the active substance(s)
are different from that of a conventional release dosage form administered by the

same route. This deliberate
modification is achieved by a special formulation design and/ or

manufacturing method.