Drug delivery systems forms

Fig. 3.20 Nanoparticulate drug delivery systems formed by amphiphilic block copolymers and their general characteristics. (From ref. [112])...

Block Copolymers are macromolecules which are composed of blocks usually in linear as it shown in Fig. 3.20, where it is illustrated a classical block copolymer. Main block copolymers are amphiphilic block copolymers having united hydrophilic blocks to hydrophobic blocks. Amphiphilic block copolymer have surfactant properties and form different kinds of associations, such as micelles, nanospheres, nanocapsules and polymersomes This tipe of association can act like excellent vehicles of several active principles. The composition, aggregate formation and the different applications of these materials have been reviewed [112], Figure 3.20 also illustrates the nanoparticulate drug delivery systems formed by amphiphilic block copolymers and their general characteristics. 

Fig. 13 Scheme of a polymeric drug delivery system formed by the simultaneous coalescence of matrix polymer and drug molecules from their common inclusion complex... 

Fig. 4.3 Plan representation of various drug delivery systems formed by self-association of amphiphilic polysaccharides in aqueous solution ( Hydrophobic domain owing to the involvement of hydrophobic groups)...

Since the development of the Spansule brand (Smith Kline Beech am) of coated beads and granules in the late 1960s, various dmg product technologies have been developed and patented to achieve extended durations of therapeutic effects. Each of these does so by various mechanisms of control of dmg release from adrninistered dosage forms. Each method has its advantages and disadvantages, a discussion of which is available in the pharmaceutical hterature (see Drug delivery systems) (21). 

Controlled-release drug delivery systems mimic nature. Molecules called lipids are found in fats and also form the membranes of living cells. A lipid molecule is similar in struc-... 

As discussed earlier, noncollagenous proteins, particularly albumin and to a lesser extent gelatin, in the form of microspheres and nanoparticles continue to be exploited as drug delivery systems. Oppen-heim (71) and Speiser (72) reviewed the technology developed to produce ultrafine particles, often referred to as nanoparticles. 

An erodible insert developed as a potential ocular drug-delivery system is marketed as a prescription drug for the lubricant properties of the polymer base. Lacrisert is a sterile ophthalmic insert used in the treatment of moderate to severe dry eye syndrome and is usually recommended for patients unable to obtain symptomatic relief with artificial tear solutions. The insert is composed of 5 mg of hydroxypropylcellulose in a rod-shaped form about 1.27 mm diameter by about 3.5 mm long. No preservative is used, since it is essentially anhydrous. The quite rigid cellulose rod is placed in the lower conjunctival sac and first imbibes water from the tears and after several hours forms a... 

Historically, the oral route of administration has been used the most for both conventional and novel drug-delivery systems. There are many obvious reasons for this, not the least of which would include acceptance by the patient and ease of administration. The types of sustained- and controlled-release systems employed for oral administration include virtually every currently known theoretical mechanism for such application. This is because there is more flexibility in dosage design, since constraints, such as sterility and potential damage at the site of administration, axe minimized. Because of this, it is convenient to discuss the different types of dosage forms by using those developed for oral administration as initial examples. 

Liposomes have been, and continue to be, of considerable interest in drug-delivery systems. A schematic diagram of their production is shown in Fig. 10. Liposomes are normally composed of phospholipids that spontaneously form multilamellar, concentric, bilayer vesicles, with layers of aqueous media separating the lipid layers. These systems, commonly referred to as multilamellar vesicles (MLVs), have diameters in the range of 15 pm. Sonication of MLVs... 

The critical void in pediatric drug therapy now lies in effective drug-delivery systems. Some inroads have been made in the manufacturing of pediatric dosing systems, particularly OTC preparations. There needs to be a redirection of the focus in nonparenteral drug formulations towards pediatric dosage forms with proven stability and bioavailability that can be easily and accurately administered to infants and children. 

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