Sustained release dosage forms

Modified-release dosage is a mechanism that (in contrast to immediate-release dosage) delivers a drug with a delay after its administration (delayed-release dosage) or for a prolonged period of time (extended-release [ER, XR, XL] dosage) or to a specific target in the body (targeted-release dosage).

Sustained release dosage forms are designed to release a drug at a predetermined rate in order to maintain a constant drug concentration for a specific period of time with minimum side effects. This can be achieved through a variety of formulations, including liposomes and drug-polymer conjugates (an example being hydrogels). Sustained release's definition is more akin to a "controlled release" rather than "sustained".

Extended-release dosage consists of sustained-release (SR) and controlled-release (CR) dosage. SR maintains drug release over a sustained period but not at a constant rate. CR maintains drug release over a sustained period at a nearly constant rate.

Sometimes these and other terms are treated as synonyms, but the United States Food and Drug Administration has in fact defined most of these as different concepts. Sometimes the term "depot tablet" is used by non-native speakers, but this is not found in any English dictionaries and is a literal translation of the term used in Swedish and some other languages.

Modified-release dosage and its variants are mechanisms used in tablets (pills) and capsules to dissolve a drug over time in order to be released slower and steadier into the bloodstream while having the advantage of being taken at less frequent intervals than immediate-release (IR) formulations of the same drug. For example, extended-release morphine enables people with chronic pain to only take one or two tablets per day.

Most commonly it refers to time dependent release in oral dose formulations. Timed release has several distinct variants such as sustained release where prolonged release is intended, pulse release, delayed release (e.g. to target different regions of the GI tract) etc. A distinction of controlled release is that not only prolongs action but it attempts to maintain drug levels within the therapeutic window to avoid potentially hazardous peaks in drug concentration following ingestion or injection and to maximize therapeutic efficiency.

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