Implantable Drug Delivery System

1. Implantable Drug Delivery Systems
Dr. Prashant L. Pingale
Associate Professor, Dept. of Pharmaceutics
GES’s Sir Dr. M. S. Gosavi College of Pharm. Edu. & Research,
Nashik-422005, INDIA

2. Content as per syllabus
Introduction,
Advantages and disadvantages,
Concept of implants and osmotic pump

3. Introduction
Drug development involves discovering, designing or modifying molecules to maximize
desirable therapeutic characteristics while minimizing untoward side effects.
Orally administered drug must be protected against denaturation in the gastrointestinal tract
and should be capable of absorption across the wall of the stomach or the intestine.
After absorption and upon reaching the portal circulation, it must be resistant to hepatic
enzymes.
The rate of drug absorption and elimination should ensure the blood levels within the
therapeutic range.

4. Introduction
Moreover, the amount of intact drug that reaches the site of action should be
sufficiently large to obtain desired therapeutic effect but insufficient to cause untoward
side effects.
Implantable drug delivery devices are devoid of aforementioned limitations associated
with oral, intravenous, topical drug administration vis-à-vis subcutaneously
implantable drug delivery devices offer one unique advantage of a retrievable
mechanism.

5. Advantages
Convenience: Effective concentration of drug in the blood can be maintained for longer
period of time by techniques such as continuous intravenous infusion or repeated injections.
Implantation treatment permits patients to get medication outside the hospital setting with
marginal medical observation.
Compliance: By reducing the frequency of drug administration over the entire period of
treatment improve patient compliance. Patient can forget to take a medicine, but drug
delivery from an implant is not dependent of patient input.

6. Advantages
Stability: Implants are environmentally stable they should not breakdown under the
influence of heat, light, air and moisture. It should be stable and safe and have good
mechanical strength.
Improved drug delivery: The drug is distributed locally or in systemic circulation with least
interference by metabolic or biological barriers. For example, the drug moiety bypassed the
GIT and the liver. The by-passing effect is beneficial to drugs, which are either easily
inactivated or absorbed poorly in the GIT and/or the liver before systemic distribution.

7. Advantages
Controlled release: Implants are available which deliver drugs by zero order
controlled release kinetics. So that dosing frequency is reduced, and patient
compliance is increased. It leads to enhanced effectiveness and reduce side effects.
Flexibility: In the choice of materials, methods of manufacture, degree of drug loading,
drug release rate etc. considerable flexibility is possible. From a regulatory viewpoint,
it is regarded as a new product and can lengthen the market protection of the drug.

8. Disadvantages
Invasive: To initiate therapy either a minor or a major surgical procedure is required to initiate therapy.
Appropriate surgical personnel is required for this, and may be time-consuming. This causes some scar
formation at the site of implantation and surgery related complications in a very small number of
patients. Uncomfortable feeling for the patient wearing the device.
Danger of device failure: There is no associated danger with this treatment that the device may for
some reason fail to work. This again requires surgical involvement to correct.
Biocompatibility issues: Concerns over body reactions to a foreign substance often increase the issues
of biocompatibility and safety of an implant.

9. Disadvantages
Termination: Osmotic pumps and non-biodegradable polymeric implants also are surgically recovered
at the end of therapy. Although surgical recovery is not required in biodegradable polymeric implants. Its
on-going biodegradation makes it difficult to end drug delivery, or to maintain the accurate dose at the
end of its lifetime.
Limited to potent drugs: In order to minimize patient’s discomfort the size of an implant is usually kept
small. Therefore most implants have a limited loading capacity so that frequently only somewhat potent
medicines such as hormones may be appropriate for delivery by implantable devices.
Possibility of adverse reactions: A high concentration of the drug delivered by an implantable device at
the implantation site may produce adverse reactions.

10. Mechanisms
Diffusion Controlled: Reservoir type of system consists of a core of drug surrounded by a
polymer and diffusion of the drug across the polymer layer is the rate limiting step. Zero order
release kinetic easily obtained. In Matrix type systems zero order release rate can be achieved
by compensating for the increase diffusional distance with an increasing area of the drug.
Chemically Controlled: The drug is distributed uniformly throughout the bio erodible
polymer, which erodes and decreases in geometry with time to allow the drug release. Zero
order kinetics can be achieved if the surface area remains unchanged with time.

11. Mechanisms
Swelling Controlled: In this type of system the release rate is equal to the product of surface
area and a rate constant corresponding to rate of advance of boundary separating the outer
shell from central core.
Osmotically Controlled: The system in the form of matrix where the core is surrounded by
semipermeable film utilizes osmotic pressure as driving force for delivery of drugs.
Magnetically Controlled: This type of system consists of drug and small magnetic beads
uniformly dispersed within a polymer matrix. In contact with aqueous media, drug is released
in diffusion-controlled manner.