Delivery systems modified release

The term modified covers several drug delivery systems. Delayed-release available other than immediately after administration (mesalazine in the colon) sustained-release slow release as governed by the delivery system (iron, potassium) controlied-release at a constant rate to maintain unvarying plasma concentration (nitrate, hormone replacement therapy). 

Controlled-release dmg delivery systems can be grouped into two main categories passive and active systems. In passive systems, dmg release rate is passive at a predetermined rate and cannot be modified after implantation unless by surgical removal of the implant. In these systems, the rate of release depends on materials used to fabricate the device, methods of fabrication, and formulation of therapeutic agent. In active dmg delivery systems, dmg release rate can be adjusted after implantation by external stimuli such as electric or magnetic fields or other ways. 

The concept of fibrous polymer formulations was extended to the delivery of aquatic herbicides (56). Several herbicides including Diquat, Fluridone, and Endothal were spun into biodegradable poly-caprolactone. Monolithic fibers and a modified monolithic system were produced with levels of herbicide from 5 to 60% by weight. Laboratory and field trials showed efficacious delivery of the active agent. Fibers provided both targeted localized delivery and controlled release of the herbicide to the aquatic weed. 

There is some confusion concerning terminology used for drug delivery when control of drug release is discussed. Within this chapter we will use an empirical approach. When a drug-delivery system does not contain any design element (formulation or process attribute) that is included to modify either spatial or... 

The drug-delivery systems are not modified or controlled release. 

Other surface-active compounds self-assemble into bilayer structures (schematically illustrated in Fig. 10b), which normally spherilize into structures termed vesicles. When vesicles are formed from phospholipids, the term liposome is used to identify the structures, which also provide useful drug delivery systems [71]. Solutes may be dispersed into the lipid bilayer or into the aqueous interior, to be subsequently delivered through a variety of mechanisms. Liposomes have shown particular promise in their ability to act as modifiers for sustained or controlled release. 

Dissolution testing has become an important component of the assessment of the quality of solid oral dosage forms and oral suspensions. The basic procedures for these oral dosage forms have been extended to transdermal delivery systems as well. The release rate for modified-release oral dosage forms adds a level of sophistication to the concept of dissolution testing, setting acceptance criteria at multiple time points. 

A buccal drug delivery system is applied to a specific area on the buccal membrane. Moreover, the delivery system ean be designed to be unidirectional in drug release so that it can be protected from the loeal environment of the oral cavity. It also permits the inclusion of a permeation enhancer/protease inhibitor or pH modifier in the formulation to modulate the membrane or the tablet-mucosal environment at that particular application site. While the irritation is limited to the well-defined area, the systemic toxicity of these enhancers/inhibitors and modifiers can be reduced. The buccal mucosa is well suited for this type of modification as it is less prone to irreversible damage [9]. In the event of drug toxicity, delivery can be terminated promptly by removal of the dosage form. 

FACTORS INFLUENCING ORAL MODIFIED-RELEASE DELIVERY SYSTEM DESIGN AND PERFORMANCE FOR WATER-INSOLUBLE DRUGS... 

Conventional systems do not offer sufficient flexibility in controlling drug-release rate and sustaining the release over time periods extending from days to months. Therefore specific modified release vaginal delivery systems are continuously under development and are based on mucoadhesive systems. Penetration enhancement may represent a necessary feature for certain delivery systems, particularly when the absorption regards a macromolecule (such as a peptide or a protein). 

H. G. Zerbe and M. Krumme. Smartrix system Design characteristics and release properties of a novel erosion-controlled oral delivery system, in Michael J. Rathbone, Jonathan Hadgraft, and Machael S. Roberts (eds.), Drugs and the Pharmaceutical Sciences, vol. 126 Modified-Release Drug Delivery Technology. New York Marcel Dekker, 2003, pp. 59-76. 

As of today, there are no commercially available pharmaceutical products of this technology. The pharmaceutical industry however, is involved in developing nanoparticle-based delivery systems. Use of nanospheres to modify the blood-brain barrier (BBB)—limiting characteristics of the drug enables targeted brain delivery via BBB transporters and provides a sustained release in brain tissue and vaccine delivery systems to deliver therapeutic protein antigens into the potent immune cells are under investigation.103... 

Compounds that show low but intrinsic absorption can be optimized by various galenic techniques and procedures. However, those which possess no absorption ability at all cannot be optimized by such procedures. New strategies have been developed for novel drag delivery systems to control drag release, transport, and absorption across mucosal membranes. A special class of modifiers are amphiphilic... 

This new type of transdermal drug delivery system is capable of releasing one or a combination of two or more skin permeation enhancers to the stratum corneum surface in order to modify the skin s barrier properties (10), prior to the controlled delivery... 

Comparative pharmacokinetic profiles of nifedipine delivered from Procardia XL, an osmotic pressure-controlled drug delivery system, once-a-day versus that from Procardia, an immediate-release dosage form, taken on time 0, 8 and 16 in human volunteers. Modified from Y.W. Chien. Oral drug delivery and delivery systems. Y.W.Chien (ed.) (1992) Novel Drug Delivery Systems. Marcel Dekker, Inc. New York, pp. 139-196... 

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