Administration, drugs membrane delivery systems

Scopolamine was the first drug to be marketed as a transdermal delivery system (Transderm-Scop) to alleviate the discomfort of motion sickness. After oral administration, scopolamine has a short duration of action because of a high first-pass effect. In addition, several side-effects are associated with the peak plasma levels obtained. Transderm-Scop is a reservoir system that incorporates two types of release mechanims a rapid, short-term release of drag from the adhesive layer, superimposed on an essentially zero-order input profile metered by the microporous membrane separating the reservoir from the skin surface. The scopolamine patch is able to maintain plasma levels in the therapeutic window for extended periods of time, delivering 0.5 mg over 3 days with few of the side-effects associated with (for example) oral administration. 

For systemic effect. Transdermal delivery systems (TDS) release drug through a rate-controlling membrane into the skin and so into the systemic circulation. Fluctuations in plasma concentration associated with other routes of administration are largely avoided, as is first-pass elimination in the... 

Following intramuscular (IM) administration, drugs must cross one or more biological membranes in order to enter the systemic circulation. Intramuscular injection is used mainly for drugs and vaccines that are not absorbed orally, for example, aminoglycosides, insulin, and hepatitis vaccine. The IM route is often used for sustained medication and specialized vehicles, such as aqueous suspensions, oily vehicles, complexes and microencapsulation, which has been developed for slow delivery of drugs by this route. ... 

Biodistribution of liposomes is a very important parameter from the clinical point of view. Liposomes can alter both the tissue distribution and the rate of clearance of the drug by making the drug take on the pharmacokinetic characteristics of the carrier (10, 11). The pharmacokinetic variables of the liposomes depend on the physiochemical characteristics of the liposomes, such as size, surface charge, membrane lipid packing, steric stabilization, dose, and route of administration. As with other microparticulate delivery systems, conventional liposomes are vulnerable to elimination from systemic circulation by the cells of the reticuloendothelial system (RES) (12). The primary sites of accumulation of conventional liposomes are the tumor, liver, and spleen compared with non-liposomal formulations (13). Many studies have shown that within the first 15-30 min after intravenous administration of liposomes between 50 and 80% of the dose is adsorbed by the cells of the RES, primarily by the Kupffer cells of the liver (14-16). 

In recent years there has been an increased interest in the utility of lipid-based delivery systems to enhance oral bioavailability (4). It is generally known that membrane permeability is directly correlated to a drug s water-lipid partition coefficient however, the systemic availability of highly lipophilic drugs is impeded by their low aqueous solubility. In an effort to improve this solubility-limited bio-availabiliy,formulators have turned to the use of lipid excipients to solubilize the compounds before oral administration. Several formulations are currently on the market, for example, Sandimmun/Neoral (cyclosporin microemulsion), Norvir (ritonavir), and Fortovase (saquinavir)... 

In membrane diffusion systems the polymer membrane with a given pore size or pore size distribution controls the diffusion of the active substance from the drug reservoir. Dosage forms with membrane-controlled drug delivery can be coated tablets, coated granules or pellets, or so-called multiparticulate systems on which various coats are applied. One possibility for transdermal drug administration is the transdermal patch controlled with a membrane [4-7,34-39]. 

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