Time Release Technology (medicine)

The term continuous release redirects here. That term may also refer to the practice of continuous integration releasing nightly builds.

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.

The first sustained-release tablets were made by Howard Press in Hoboken, New Jersey in the early 1950s. The first tablets released under his process patent were called "Nitroglyn" and made under license by Key Corp. in Florida.

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.

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.

The difference between controlled-release and sustained-release is that controlled-release is a perfectly zero-order release; that is, the drug releases over time irrespective of concentration. Sustained-release implies slow release of the drug over a time period; it may or may not be a controlled-release.

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