ER = Extended Release
SR = Sustained Release
Time release technology, also known as sustained-release (SR), sustained-action (SA), extended-release (ER, XR, or XL), time-release or timed-release, controlled-release (CR), modified release (MR), or continuous-release (CR or Contin), is a mechanism used in pill tablets or capsules to dissolve slowly and release a drug over time. The advantages of sustained-release tablets or capsules are that they can often be taken less frequently than instant-release formulations of the same drug, and that they keep steadier levels of the drug in the bloodstream.
Today, most time-release drugs are formulated so that the active ingredient is embedded in a matrix of insoluble substance(s) (various: some acrylics, even chitin; these substances are often patented) such that the dissolving drug must find its way out through the holes in the matrix. Some drugs are enclosed in polymer-based tablets with a laser-drilled hole on one side and a porous membrane on the other side. Stomach acids push through the porous membrane, thereby pushing the drug out through the laser-drilled hole. In time, the entire drug dose releases into the system while the polymer container remains intact, to be later excreted through normal digestion.
In some SR formulations, the drug dissolves into the matrix, and the matrix physically swells to form a gel, allowing the drug to exit through the gel's outer surface.
Micro-encapsulation is also regarded as a more complete technology to produce complex dissolution profiles. Through coating an active pharmaceutical ingredient around an inert core, and layering it with insoluble substances to form a microsphere you are able to obtain more consistent and replicable dissolution rates in a convenient format you can mix and match with other instant release pharmaceutical ingredients in to any two piece gelatin capsule.
There are certain considerations for the formation of sustained-release formulation:
* If the active compound has a long half-life (over 6 hours), it is sustained on its own.
* If the pharmacological activity of the active compound is not related to its blood levels, time releasing has no purpose.
* If the absorption of the active compound involves an active transport, the development of a time-release product may be problematic.
* Finally, if the active compound has a short half-life, it would require a large amount to maintain a prolonged effective dose. In this case, a broad therapeutic window is necessary to avoid toxicity; otherwise, the risk is unwarranted and another mode of administration would be recommended.
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