Retentive delivery systems

Design of Retentive Delivery System Based on Size 177... 

Future Potential for Gastric Retentive Delivery Systems 195... 

Physiological Rationale for Gastric Retentive Delivery System Design GI Motility... 

The buccal mucosa comprises an expanse of smooth and relatively immobile surface and thus is ideally suited to the use of retentive delivery systems. In contrast, the sublingual mucosa is unsuitable for adhesive dosage forms for a number of reasons, including ... 

Abdellatif et al. reported a method for data retention [56] in which collected electronic data forms of each participating site are saved on a read-only CD as PDF files after the site s database has been locked. SAS Output Delivery System (ODS), PROC Template, and PROC Forms were used to construct a read-only CD of the data forms in a PDF format for each site and then sent to the site s PI. 

The solvent delivery system is one of the most important components of the liquid chromatograph since its performance directly affects retention time reproducibility d detector baseline stability [1,2,39,40]. As well as the pump, other components such as check valves, flow controllers, mixing... 

In summary, the advantages of our approach to studying gastric retention are twofold. First, hydrogel response to the gastric environment can be noninvasively visualized in real-time. Second, a more efficient and justifiable approach to the development of long-term oral drug delivery systems can be achieved. 

SH Gehrke, LH Uhden, JF McBride. Enhanced loading and activity retention in hydrogel delivery systems. J Controlled Release. 21-33 (1998). 

Nanosized objects perform various functions in the biomedical field. In the human body, nanosized particulate substances behave very differently from larger particles. In 1986, Maeda et al. found that the stained albumin, having a size of several nanometers, naturally accumulates in the region of cancerous tissues, which is now well known as the enhanced permeability and retention (EPR) effect. Many studies in the field of nanoparticles are based on this finding. Another application of nanoparticles is the delivery system using various polyplexes that are composed of carrier molecules and plasmid DNA or nucleic acid drugs such as antisenses and siRNA. In addition, nanofibers are mainly used for biodegradable scaffolds in tissue... 

Hwang, S.J., Park, H., and Park, K., Gastric retentive drug-delivery systems, Crit. Rev. Ther. Drug Carr. Syst., 15 243-284 (1998). 

Stimulation of saliva production is under sympathetic and parasympathetic control. Parasympathetic stimulation produces a serous watery secretion, whereas sympathetic stimulation produces much thicker saliva. Drug delivery systems, therefore, should not be placed over a duct or adjacent to a salivary duct, as this may dislodge the retentive system or may result in excessive wash-out of the drug or rapid dissolution/erosion of the delivery system making it difficult to achieve high local drug concentrations. If a retentive system is placed over salivary ducts, the reduced salivary flow rate may produce less or no mucus which is required for the proper attachment of a mucoadhesive delivery device. 

Desmopressin (the synthetic analog of vasopressin) acts by increasing water retention and urine concentration in the distal tubules of the kidney. This drug is administered intranasally (20-40 pg or one to two sprays) using a unit-dose, spray pump delivery system. The duration of action is 10 to 12 hours. The medication is expensive. 

Singh, B.N., and K.H. Kim. 2000. Floating drug delivery systems an approach to oral controlled drug delivery via gastric retention. J Control Release 63 235. 

Soppimath, K.S. 2001. Microspheres as floating drug-delivery systems to increase gastric retention of drugs. Drug Metab Rev 33 149. 

Bioadhesive formulations and microsphere delivery systems in particular have attracted much attention. As drug formulations are usually rapidly removed from the site of deposition by the mucociliary clearance, increasing the retention time of drug in the nasal cavity via bioadhesion can increase bioavailability [28], Bioadhesion may be defined as the ability of a material (synthetic or biological) to adhere to a biological tissue for an extended period of time. When applied to a mucous membrane, a bioadhesive polymer may adhere primarily to the mucus layer or epithelial cell surface in a phenomenon known as mucoadhesion [29,30]. The bioadhesive properties of a wide range of materials have been evaluated over the last decade. 

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