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

Controlled release

Controlled release is a term referring to the presentation or delivery of compounds in response to stimuli or time. This can be for purposes in several areas including agriculture, cosmetics and personal care, pharmaceuticals and food science. Most commonly it refers to time dependent release in...

(CR), modified release (MR), or continuous-release (CR or Contin), is a mechanism used in pill tablet

Tablet

A tablet is a pharmaceutical dosage form. It comprises a mixture of active substances and excipients, usually in powder form, pressed or compacted from a powder into a solid dose...

s or capsules to dissolve

Solvation

Solvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...

 slowly and release a drug

Drug

A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

 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

Active ingredient

An active ingredient is the substance of a pharmaceutical drug or a pharmaceutical ingredient and bulk active in medicine; in pesticide formulations active substance may be used. Some medications and pesticide products may contain more than one active ingredient...

 is embedded in a matrix of insoluble substance(s) (various: some acrylics

Acryl group

In organic chemistry, the acryloyl group is the functional group with structure H2C=CH–C–; it is the acyl group derived from acrylic acid. The preferred IUPAC name for the group is prop-2-enoyl, and it is also known as acrylyl or simply acryl...

, even chitin

Chitin

Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...

; 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 excreted later 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

Micro-encapsulation

Micro-encapsulation is a process in which tiny particles or droplets are surrounded by a coating to give small capsules many useful properties. In a relatively simplistic form, a microcapsule is a small sphere with a uniform wall around it...

 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

Capsule

-Anatomy:* an eggshell* Articular capsules - every diarthrodial joint possesses a fibrous or ligamentous capsule, lined with synovial membrane, attached to the adjacent ends of the articulating bones* the sac that encloses the crystalline lens of the eye...

.

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
  Active transport
  Active transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
  
  , 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.