By Dr. Shruti Bhat
In the past, many terms viz. time-release, pulse-release, prolonged-release, sustained release, controlled release etc. have been used to refer to therapeutic systems. However, “sustained” and “controlled” release represent separate delivery processes. “Sustained release” systems describe a drug delivery system with delayed and / or prolonged release of drug. It also implies delayed therapeutic action and sustained duration of therapeutic effect.
“Controlled release” implies a predictability and reproducibility in the drug release kinetics. In other words, sustained release dosage forms provide medication over an extended time period whereas controlled release systems attempt to control drug concentrations on the target tissue. Site-specific systems and targeted delivery systems are the descriptive terms used to denote this type of delivery control.
CLASSIFICATION OF CONTROLLED RELEASE SYSTEMS:
Broadly, controlled release systems can be classified into two categories:
1) Based on Route of Administration:
· Peroral dosage forms
· Dental Systems
· Ocular systems
· Vaginal and Uterine systems
· Injections and implants
2) Based on Formulation Aspect:
· Polymer based CR technology (dissolution/diffusion controlled)
· Osmotic pumps
· Mechanical pumps
· Biodegradable carrier based CR system
· Ion-exchange system
· Prodrug approach
· Micro emulsion / Multiple emulsions
· Design of Controlled - Release Drug Delivery SYSTEM:
The design of controlled - released drug delivery system (CRDDS) accounts three important criteria viz. drug, delivery and destination. CRDDS can be designed using open or closed loop systems.
OPEN LOOP SYSTEM:
These systems comprise a drug platform; a reservoir, where the drug is stored; an energy source and in more sophisticated systems, a therapeutic program which meters the amount of agent passing through the rate-controlling mechanism. Once the agent gets into the biological environment, a pharmacokinetic process occurs before distinguishable therapeutic and side actions manifest themselves.
CLOSED LOOP SYSTEM:
In more complex closed loop systems, the pharmacokinetic process-taking place systemically is feed back to the drug delivery system. This mechanism instructs the delivery system to alter its therapeutic program appropriately. These systems are more complicated than open-loop systems because they require a very sensitive sensor in the biological environment that is capable of sending a negative feed back signal to the delivery system.
To date, most research in controlled release has involved an open-loop system. The design of the loop in turn is based on the pathway of drug distribution / disposition in the body.
Numerous molecules have been developed as controlled release formulations. I have developed close to 50 controlled / modified released products and the products are doing extremely well in the markets globally.
By Dr. Shruti Bhat