Controlled drug delivery systems:


Controlled drug delivery - Controlled drug delivery can be defined as the delivery of the drug at a predetermined rate, for locally or systemically, for a certain and specified time period. A controlled release system includes any delivery system that achieves slow release of the drug over an extended period of time. This is the way to be achieved by better control of plasma drug level and less frequent dosing. The rationalization for the development of controlled release drug delivery system of a drug is to improve its therapeutic benefits, minimizing the side effects of drugs even as improving the management of the diseased condition





Controlled release formulation – Controlled-Release (CR) formulations (dosage form) are absorbed slower than conventional tablets and produce more stable serum levels. The controlled drug delivery system delivers drug at a predetermined rate for a specific time. Peak serum concentrations are usually attained within 4–8 hours with plain tablets.


Repeat action preparation – this dosage forms are the type of extended-release dosage form. They usually contain two or three single doses of medication, one for immediate release and one for delayed release, if there is third single dose, it also release after a certain time.


Extended release formulation - this type of dosage forms allows at least a twofold reduction in dosage frequency as compared to that drug presented as an immediate-release (conventional) dosage form. Examples of extended-release dosage forms include controlled-release, sustained-release, and long-acting drug products.


Delayed release preparation - Delayed-release drugs have a release time similar to those of conventional drugs, but the medication does not release the API immediately. Example enteric coated dosage forms.


Targeted release drug product - Targeted drug delivery system is a special dosage form of drug delivery system where the medicament is selectively targeted or delivered only to its site or near the site of action. These dosage forms are either immediate or extended characteristics.



Controlled action system – This system provides a prolonged duration of drug release. The drug release kinetics is predictable.


Sustained action system - A drug in tablet form that provides the required dosage initially and then maintains or repeats it periodically at desired intervals.


Prolonged action system - prolonged release formulations (tablets/capsules) are aimed at delaying in administration and dissolve at a slower and constant rate into the body system. The main drawback of this system is it does not maintain the constant serum level.




Rationale – The logical reason for a procedure is known as RATIONALE.


The primary rationale of a controlled release drug delivery system is to optimize the biopharmaceutics, pharmacokinetics, and pharmacodynamics properties of a drug by using novel drug delivery system or altering the structure of molecules. An ideal drug delivery system should deliver the drug at a controlled rate by the need of body over a specified period of treatment.


The importance of medical rationale for the development of controlled drug delivery system are for following aspects:


Reduced dosing frequency – The conventional dosage forms have limit for the dosage frequency. This problem can be resolved by using controlled release dosage form of preparation that release drug over an extended time and maintains the desired drug concentration in blood.


Minimization of fluctuation of plasma concentration – When conventional dosage form like tablets and capsules are used the fluctuation of plasma concentration is noticed, this can be avoided by using CRDDS (Controlled Release Drug Delivery System).


Better patient compatibility – designing a dosage regimen for a drug influences its duration of action, bioavailability, absorption rate, and elimination.


Biological Rational:


Absorption – The efficiency of absorption is varying throughout the GIT, which directly effects the extent of drug absorption from the site.

Most of the drugs are poorly soluble and poorly permeable.


Distribution – Distribution of drug from the conventional dosage form directly gets distributed throughout the body and accumulated on some sites, this causes toxicity, it can be prevented by CRDDS.


Elimination – Most of drugs when used, they accumulate in the organs like liver, pancreas etc. and become fatal sometimes. The removal of these unwanted accumulated substances is hectic for the system due to slow elimination rate. In such situation the CRDDS plays important roles.




• Reduction in frequency of drug administration

• Improved patient compliance

• Elimination of over or low dosing effects

• Reduction in drug level fluctuation in blood

• Reduction in total drug usage when compared with conventional therapy

• Reduction in drug accumulation with chronic therapy

• Reduction in drug toxicity

Improve bioavailability of drugs.



• Formulation cost is high

• It decreases systemic availability due to incomplete release of drug.

• Barriers to drug delivery in tumors

• Challenges and barriers of ocular drug delivery

• Formulation design of poorly soluble drugs

• Pharmaceutical equipment & drug release testing

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