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 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, one can obtain more consistent and replicable dissolution rates in a convenient format that can be mixed and matched with other instant release pharmaceutical ingredients into any two piece gelatin
capsule. There are certain considerations for the formation of sustained-release formulation: • If the pharmacological activity of the active compound is not related to its blood levels, time releasing has no purpose except in some cases, such as bupropion, to reduce possible side effects. • If the absorption of the active compound involves an
active transport, the development of a time-release product may be problematic. The
biological half-life of the drug refers to the drug's elimination from the bloodstream which can be caused by metabolism, urine, and other forms of excretion. If the active compound has a long half-life (over 6 hours), it is sustained on its own. 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. Appropriate half-lives used to apply sustained methods are typically 3–4 hours and a drug dose greater than 0.5 grams is too high. The
therapeutic index also factors whether a drug can be used as a time release drug. A drug with a thin therapeutic range, or small therapeutic index, will be determined unfit for a sustained release mechanism in partial fear of
dose dumping which can prove fatal at the conditions mentioned. For a drug that is made to be released over time, the objective is to stay within the therapeutic range as long as needed. • Matrix devices forms a matrix (drug(s) mixed with a gelling agent) where the drug is dissolved/dispersed. Osmotic release systems have a number of major advantages over other controlled-release mechanisms. They are significantly less affected by factors such as
pH, food intake,
GI motility, and differing intestinal environments. Using an osmotic pump to deliver drugs has additional inherent advantages regarding control over drug delivery rates. This allows for much more precise drug delivery over an extended period of time, which results in much more predictable
pharmacokinetics. However, osmotic release systems are relatively complicated, somewhat difficult to manufacture, and may cause irritation or even blockage of the GI tract due to prolonged release of irritating drugs from the non-deformable tablet.
Ion-exchange resin In the ion-exchange method, the resins are cross-linked water-insoluble polymers that contain ionisable functional groups that form a repeating pattern of polymers, creating a polymer chain.
Bio-adhesive systems Bio-adhesive systems generally are meant to stick to mucus and can be favorable for mouth based interactions due to high mucus levels in the general area but not as simple for other areas. Magnetic materials can be added to the drug so another magnet can hold it from outside the body to assist in holding the system in place. However, there is low patient compliance with this system. • A lipid matrix uses wax or similar materials. Drug release happens via diffusion through, and erosion of, the wax and tends to be sensitive to digestive fluids. and electronic control of
MEMS and
NEMS. Spherical hydrogels, in micro-size (50-600 μm diameter) with 3-dimensional cross-linked polymer, can be used as drug carrier to control the release of the drug. These hydrogels are called microgels. They may possess a negative charge as example DC-beads. By ion-exchange mechanism, a large amount of oppositely charged amphiphilic drugs can be loaded inside these microgels. Then, the release of these drugs can be controlled by a specific triggering factor like pH, ionic strength or temperature. == Pill splitting ==