Drug absorption dosage form

This time controlled release tablet with a designated lag time followed by a rapid release may provide an alternative to site-specific delivery of drugs with optimal absorption windows or colonic delivery of drugs that are sensitive to low pH or enzyme action for the treatment of localized conditions such as ulcerative colitis, Crohn s disease, and irritable bowel syndrome (IBS). Also, by controlling a predetermined lag time of drug from dosage form, the release behavior can be matched with the body s circadian rhythm pattern in chronotherapy. 

The absorption rate constant is a constant for a given drug formulation, dosage form and route of administration. That is, the same drug... 

Reppas, C., Shah, V. P. Dissolution testing as a prognostic tool for oral drug absorption immediate release dosage forms. Pharm. Res. 1998, 15, 11-22. 

The fact that the GIT is so well perfused by the bloodstream permits efficient delivery of absorbed materials to the body. As a result of this rapid blood perfusion, the blood at the site of absorption represents a virtual sink for absorbed material. Under normal conditions, then, there is never a buildup in drug concentration in the blood at the site of absorption. Therefore, the concentration gradient will favor further unidirectional transfer of drug from the gut to the blood. Usually, then, blood flow is not an important consideration in drug absorption. Generally, the properties of the dosage form (especially dissolution rate) or the compound s inherent absorbability will be the limiting factors in absorption. 

As discussed previously, drug absorption may be impaired or improved when food is present in the GIT. Food may reduce the rate or extent of absorption by virtue of reduced gastric-emptying rate, which is particularly important for compounds unstable in gastric fluids and for dosage forms designed to release drug... 

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