Release characteristics

Werner complexes can be used to form clathrates with the Cg aromatic isomers (35—42). The aromatic compounds are released upon heating. Since the uptake and release characteristics of the four Cg aromatic isomers are each different, this method has been suggested as a means of separating the isomers. 

Another advantage of the membrane plate is its flexibiUty to cake thickness, ie, thinner cakes can be easily handled without loss of dryness. Cake release characteristics are also improved by deflation of the membrane prior to cake discharge. Alternating arrangements, in which the membrane plates and the normal recessed plates alternate, have been used to reduce cost. 

Plasticizers (qv) are usually present at lower concentrations compared to general-purpose mbber-based compounds, because of their volatility at typical ACM service temperatures and/or their partial extractabiflty by the aggressive fluids where acryflc elastomers are employed. Other additives are therefore required to improve processibiflty. These processiag aids act as lubricating agents and enhance the release characteristics of the acryflc compound and/or reduce compound viscosity. 

One of the important breakthroughs in the silicone PSA industry has been the development of new release liners based on fluorosilicones [116]. These new materials significantly improve the release characteristics of the silicone PSAs, something that has been difficult to achieve because of the high adhesion silicone PSAs show to low energy substrates, including silicone rubbers and liners. 

Selecting the suitable mechanism largely depends on the release characteristics of the cake from the filter media. Scraper discharge mechanisms generally tend to suit cakes that release readily whereas roller discharge mechanisms are best suited for cakes that exhibit thixotropic behavior. 

The Modeling Engine in THERdbASE has the following model groups 1) Population Distributions, 2) Location/Activity Patterns, 3) Food Consumption Patterns, 4) Agent Releases Characteristics, 5) Microenvironment Agent Concentrations, 6) Macroenvironment Agent Concentrations, 7) Exposure Patterns and Scenarios, 8) Dose Patterns, and 9) Risk Assessment. 

A simple example of gel formation is provided by chitosan tripolyphosphate and chitosan polyphosphate gel beads the pH-responsive swelling abihty, drug-release characteristics, and morphology of the gel bead depend on polyelectrolyte complexation mechanism and the molecular weight. The chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution by ionotropic cross-hnking or interpolymer complexation, respectively. 

Spenlehauer, G., Vert, M., Benoit, J. P., Chabot, F., and Veillard, M., Biodegradable cisplatin microspheres prepared by the solvent evaporation method Morphology and release characteristics, J. Control. Rel., 7, 217, 1988. 

Deong, K. W., Brott, B. C., and Danger, R., Bioerodible polyanhydrides as drug-carrier matrices. I. Characterization, degradation and release characteristics, J. Biomed. Mater. Res., 19, 941-955, 1985. 

The effect of various chemical modifications on the mechanical properties of reconstituted collagen and the diffusion rates of the steroid medroxyprogesterone was investigated (38). Formaldehyde-treated films, which are heavily crosslinked, have high moduli and low rates of drug release. Films treated with chrome quickly become hydrated in solution and have low moduli and very rapid drug release characteristics. 

Neural networks have also been used in Slovenia, to model the release characteristics of diclofenac [52] in China, to study release of nifedipine and nomodipine [53] and in Yugoslavia to model the release of aspirin [54], More recently, work in this area has been extended to model osmotic pumps in China [55] and enteric coated tablets in Ireland [56],... 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

Figure 4. Effect of polymerization conditions on the release characteristics of the insulin/poly(acrylic acid) resin system.

It may sometimes by necessary to supplement the properties of the drug so that it compresses more easily, and these needs have been realized by several manufacturers of excipients. Materials described as compression aids are now commercially available. Ideally, such adjuvants should develop mechanical strength while improving, or at least not adversely affecting, release characteristics. Among the most successful at meeting both these needs have been the microcrystalline celluloses (partially acid-hydrolyzed forms of cellulose). A number of grades are available based upon particle size and distribution. 

J. Freyfuss, J. M. Shaw, and J. J. Ross, Jr., Fluphe-nazine enanthate and fluphenazine decanoate intramuscular injection and esterification as requirements for slow-release characteristics in dogs, J. Pharm. Sci., 65, 1310-1315 (1976). 

However, in the foregoing systems, the predominant mechanism allows easy mathematical description. In practice, the dominant mechanism for release will overshadow other processes enough to allow classification as either dissolution rate-limited or diffusion-controlled. Bioerodible devices, however, constitute a group of systems for which mathematical descriptions of release characteristics can be quite complex. Characteristics of this type of system are listed in Table 7. A typical system is shown in Fig. 8. The mechanism of release from simple erodible slabs, cylinders, and spheres has been described [36], A simple expression describing release from all three of these erodible devices is... 

Atmospheric information, including local climate (precipitation, temperature, wind speed and direction, presence of inversion layers), weather extremes (storms, floods, winds), release characteristics (direction and speed of plume movement, rate, amount, and temperature of release, relative densities), and types of atmospheric hazards and hazards assessment... 

As noted earlier, perhaps the key determinant of the overall release characteristics from an osmotic pump system is the solubility of the drug. If the solubility of the drug is too low, then the total dose that can be delivered is limited. If the solubility is too high, then the percent of the total dose that can be delivered at a zero-order rate can be relatively small. For example, as shown by Theeuwes [10], the fraction of the total dose (F) that can be delivered at a zero-order rate is given by... 

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