Modified Release Dosage Forms
The term “modified release” means alteration in the release of the drug substance based on the time, course or duration. This is particularly useful for pro-drugs or poorly soluble drugs where release is dependent either on the environment of the different regions of the body or factors that governs the conversion of one product into the another for the therapeutic action. Unlike immediate release (conventional forms) drug products which involve direct absorption and onset of action, it is more cumbersome to develop modified release drug products where rate of transfer of drug substance in the body is adjusted for effective therapeutic response.
Different types of modified release dosage forms are:
- 1. Extended Release Dosage Form: It is a type of dosage form in which release of drug is in controlled manner at a predetermined rate, duration and location to achieve and maintain optimum therapeutic blood levels of the body. The main rationale behind development of extended release is to allow reduction in the frequency of the doses. They are generally recognised by two different types: Controlled and Sustained Release. In controlled release drug is delivered at a predetermined rate over a longer period of time whereas in sustained release the release of drug is at a slow pace over an extended period of time but not particularly at a predetermined rate.
A) Controlled Release
B) Sustained Release:
- 2. Delayed Release Dosage Form: This form is designed to release the portion of the drug promptly after administration and discrete portions of the drug other than promptly after administration. the delay may be based on the time or gastrointestinal pH. For example enteric coated dosage forms. the main rationale behind development of these type of dosage form is to protect from the gasrtic distress or facilitate GI transit of drugs better absorbed in intestinal fluid.
The above diagram depicts the lag time during which there is no therapeutic response (as pm) and release of drug after delayed period of time (as early am)
- 3. Target Release Dosage Form: This type of dosage form releases the drug at or near the intended site of action. This may be instant or it may have extended release characteristics. The rationale behind is to increase the concentration of the drug at particular site that others which will certainly lead to lesser side effects and improved efficacy. For example: Liposomes, Nanocrystals.
- 4. Repeat Action Dosage Form: This type of dosage form usually contains two single doses of medication in which one is of immediate release and second of extended release. Mostly prepared by forming layers in which first layer is immediately dissolved followed by slowly permeable barrier coating. The rationale behind development of such dosage forms is for the chronic situations that requires repeated dosing.