Sustained drug release

YoUes, S., and Sartori, M. F., Degradable polymers for sustained drug release, in Drug Delivery Systems (R. L. Juliano, ed.), Oxford University Press, New York, 1980, pp. 84-111. 

A number of the water-soluble polymers also have adhesive properties which are being extensively evaluated for drug delivery (9). These polymers will adhere to the mucous coating in the gastrointestinal tract, the nose, and the mouth to delay passage and sustain drug release. Those polymers with the best adhesive properties are those with hydroxyl and carboxyl groups. Table II lists some of the bioadhesive polymers and their adhesive properties. 

CNS-related disorders, sustained drug release for, 9 82-83 CO2. See also Carbon dioxide absorption of, 23 598-599 as an alternative refrigerant, 27 533 removal by alkanolamines, 23 597-600 CO2 emissions, from FCC unit regenerators, 77 720-721 CO2 flooding, in oil recovery, 78 615-617 CO2 removal unit, 70 646, 648 CO2 stimulation, in oil recovery, 78 617 CO-896, chain length and linearity, 2 12t CO-1270, chain length and linearity,... 

Sustained Drug Release from Solid, Semisolid, and Liquid Formulations... 

Sustained release from disperse systems such as emulsions and suspensions can be achieved by the adsorption of appropriate mesogenic molecules at the interface. The drug substance, which forms the inner phase or is included in the dispersed phase, cannot pass the liquid ciystals at the interface easily and thus diffuses slowly into the continuous phase and from there into the organism via the site of application. This sustained drug release is especially pronounced in the case of multilamellar liquid crystals at the interface. 

J. M. Conrad, and J. R. Robinson. Sustained drug release from tablets and particles through coating, in H. A. Lieberman and L. Lachman (eds.), Pharmaceutical Dosage Forms Tablets, Vol. 3. New York Marcel Dekker, 1982, pp. 149-221. 

Figure 2. Cross-section of different designs of hydrogel carriers for sustained drug release. Drug/polymer concentration c.

A sustained drug release is favourable for drugs with short elimination half-life. It can be controlled by hydration and diffusion mechanisms or ionic interactions between the drug and the polymeric carrier. In the case of diffusion control the stability of the carrier system is essential, as its disintegration leads to a burst release. Therefore, the cohesiveness of the polymer network plays a crucial role in order to control the release over several hours. Due to the formation of disulphide bonds within the network thiomers offer adequate cohesive stability. Almost zero-order release kinetics could be shown for insulin embedded in thiolated polycarbophil matrices (Clausen and Bernkop-Schnurch 2001). In the case of peptide and protein drugs release can be controlled via ionic interactions. An anionic or cationic polymer has to be chosen depending... 

The resins are prepared first by copolymerizing styrene (ST) and divinylbenzene (DVB), resulting in a cross-linked polystyrene. Usually, they are produced in the form of spherical beads. These beads are sulfonated with sulfuric acid for anionic resins and methylated with chloromethyl ether followed by quatemization with trimethylamine for cationic resins. Two types of resins exist gel and microporous. The microporous beads are used to remove ionic substances quickly while the gel-type beads are used for sustaining drug release over a long period of time. 

Microparticles Spray drying Propranolol hydrochloride CH-PVM/MA In vitro Sustained drug release 45... 

In order to achieve a sustained drug release and a prolonged therapeutic activity, nanoparticles must be retained in the cul-de-sac and the entrapped drug must be released from the particles at a certain rate. If the release is too fast, there is no sustained release effect. If it is too slow, the concentration of the drug in the tears might be too low to achieve penetration into the ocular tissues [208]. The major limiting issues for the development of nanoparticles include the control of particle size and drug release rate as well as the formulation stability. 

Chitosan, chitosan/ ethylcellulose In vitro Moderate swelling behavior, sustained drug release 107... 

Solid formulations for sustained drug release may contain mesogenic polymers as excipients. The mesogenic polymers form a matrix, which is usually compressed into tablets. Some of the most frequently used excipients for sustained release matrices include cellulose derivatives, which behave like lyotropic liquid crystals when they are gradually dissolved in aqueous media. Cellulose derivatives such as hydroxy-propyl cellulose or hydroxy-propylmethyl cellulose form gel-like lyotropic mesophases in contact with water, through which diffusion takes place relatively slowly. Increasing dilution of the mesophase with water transforms the mesophase to a highly viscous slime and then to a colloidal polymer solution. 

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