Absorption site-specific

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

Implementation of dissolution testing by BP was in a tiered program similar to that employed at the time by USP. For the first category, products would conform to 75% release in 45 min. Where the drug had a narrow therapeutic index and should not release too rapidly, was known to exhibit a brief plasma half-life, or have site-specific absorption, additional testing to satisfy the need for greater control would be considered. Dissolution tests were included in 1980 for 14 tablet and four capsule monographs (15,16). 

Sinko et al. [92] established an Intestinal and Vascular Access Port (IVAP) model where dogs were fitted with three intestinal catheters for site-specific administration to various section of the intestine (i.e. duodenum, ileum, and colon), one vascular catheter for access to the portal vein, and a peripheral vein (e.g. branchial) for IV access. The animals were allowed to recover for 2 weeks prior to initiation of studies. The extent of intestinal versus hepatic first-pass metabolism was determined by comparing blood levels following intra-duodenal (AUQ.d.) versus portal (AUVi.p.v.) versus intravenous (AUQ.V.) administration. The model also lends itself to a comparison of the impact of site-specific preferential absorption, and hence a determination of the optimal site for intestinal delivery. 

Rouge N, Buri P, Doelker E (1996) Drug absorption sites in the gastrointestinal tract and dosage forms for site-specific delivery. Int J Pharm 136 117-139... 

Hwang KK, Jiang L, Ren Y, Martin LL, Martin NF (2002) Site-specific absorption of M100240 and MDL 100,173 in rats evaluated using Sweetana-Grass diffusion chamber technology. J Pharmacol Toxicol Methods 48 97-101. 

Terao T, Matsuda K, Shouji H (2001) Improvement in site-specific intestinal absorption of furosemide by Eudragit L100-55. J Pharm Pharmacol 53 433 140... 

A high concentration of Ca in the intestinal lumen relative to the ECF tends to drive Ca absorption via the paracellular route. Water naturally seeps through the "microspaces (Wasserman, 2004), or cellular jimctions between adjacent enterocytes, during absorption thus creating a paracellular pathway between which 8-30% of the total Ca absorbed (McCormick, 2002) is entrained as a solute. The transfer of Ca by a solvent drag-induced mechanism is via a passive diffusion process in response to increases in the osmolarity of the lumenal contents. This pathway is not site specific and the opportunity for Ca absorption via this route occurs throughout the entire length of the small intestine (Weaver and Liebman, 2002). 

Drug release and retention at the site of absorption are very important for the enhancement of the bioavailability, particularly when the absorption sites are localized to a certain area of the GI route. This control of the transition of the drug can be achieved using bioadhesive excipients. Chlorothiazide (CT), a diuretic and antihypertensive drug, was better orally absorbed when administered with mucoadhesive polymers [25], The absorption of CT is considered to be saturable and site-specific, because a low dose is better absorbed, and a decreased stomach emptying rate and slow GI transition rate are better for increased absorption. As chitosan is a mucoadhesive polymer, the absorption of CT is expected to be enhanced... 

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. 

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