Gradual release

A monolithic system is comprised of a polymer membrane with dmg dissolved or dispersed ia it. The dmg diffuses toward the region of lower activity causiag the release of the dmg. It is difficult to achieve constant release from a system like this because the activity of the dmg ia the polymer is constantly decreasiag as the dmg is gradually released. The cumulative amount of dmg released is proportional to the square root of time (88). Thus, the rate of dmg release constantly decreases with time. Again, the rate of dmg release is governed by the physical properties of the polymer, the physical properties of the dmg, the geometry of the device (89), and the total dmg loaded iato the device. 

Antimony (Sb) and tin (Sn) are usually not added to the active material, but both are alloying components of the grid. They are gradually released from the grid by corrosion, and permeate the active material by dissolution and diffusion. 

PA-4,6 salt is prepared from adipic acid and 1,4-tetramethylenediamine as described for the PA-6,6 salt (Example la). PA-4,6 salt (20 g), 2 mL water, and 0.2 mL 1,4-tetramethylenediamine (2.1 mol % excess) are added to a 100-mL glass container in an autoclave. The autoclave is flushed with nitrogen, closed, and given a starting nitrogen pressure of 5 bar. The autoclave is heated over a period of 60 min to 180° C and maintained at that temperature for 100 min, when the pressure is increased to about 8 bar. The pressure is then gradually released, the reaction mass cooled, and the material removed from the autoclave. The prepolymer is crushed into small particles (0.1—0.2 mm) (see Example lb). This prepolymer has a relative viscosity (r]rd) of 1.3 as measured in 96% sulfuric acid (1% solution at 25° C). 

As discussed earlier the whole process is a redox reaction. Selenium is reduced using sodium borohydride to give selenide ions. In the above reaction, the metal ion reacts with the polymer (PVP or PVA) solution to form the polymer-metal ion solution. Addition of the selenide ion solution to the polymer-metal ion solutions resulted in instantaneous change in the colour of the solutions from colourless to orange (PVA) and orange red (PVP). This indicates the formation of CdSe nanoparticles. The addition of the selenide solution to the polymer - metal ion solution resulted in gradual release of selenide ion (Se -) upon hydrolytic decomposition in alkaline media (equation 4). The released selenide ions then react with metal ion to form seed particles (nucleation). 

Dendron 32 was incubated in phosphate buffer saline, pH 7.4, in the presence and in the absence of PGA. The progress of the disassembly was monitored by RP-HPLC, and the results are presented in Fig. 5.27. Tryptophan was gradually released from dendron 32 upon incubation with PGA. The release was completed within 48 h in the presence of PGA the control reaction without PGA showed no release at all. Although the disassembly of this dendron occurred more slowly under physiological conditions than dendron 31 in the MeOH/DMSO environment (Fig. 5.24), PGA cleaved its phenylacetamide substrate from dendron 32 and the resulting amine intermediate was disassembled to release the total six molecules of tryptophan. 

The proteins in the mortars can be modified by gradual oxidation or other chemical processes. In mass spectra the peaks that can be interpreted as oxygen incorporation (the mass shift of +16 Da) or ammonia release (—15 Da) can be sometimes indicated. This observation is not surprising as several amino acids (Met, Trp, Tyr, etc.) can be oxidised under these conditions similarly, Gin and Asn can gradually release their ammonia by long-term hydrolysis in a wet inorganic matrix. 

The monofunctional adduct formed between c/s-[Pt(NH3)2(4-Me-Py)Cl]+ and heptamer duplex 5 -d(CCTG TCC) d(GGACAGG) is unstable, and the platinum moiety is gradually released from DNA (65). Similarly, a slow dissociation of platinum from the single-stranded... 

The solubility of C60 and C70 fullerenes in vegetable oils will permit to employ these molecules for topical use in creams, lotions and ointments, which are adsorbed by skin. Vegetable oils, especially olive oil, are considered excellent excipients for injectable preparation where the active principle is soluble in fats. Their absorption in the subcutaneous tissues is slow and limited and ensures a gradual release of the active principle (Adami, 1960). 

The C60 and C70 reactivity with the vegetable oils at first glance could appear as an obstacle in the use of fullerene solutions in vegetable oils. Apart from the fact that one could use fully saturated fatty acids derivatives as vehicle for fullerenes delivery, which are not reactive with them, the formation of adducts between the unsaturated fatty acids and fullerenes could be exploited not only in the stabilization of the systems fullerenes-vegetable oils, but also in the alteration and, may be in the attenuation of the fullerene reactivity in in vivo and in a very gradual release of the fullerenes-fatty acids derivatives in living systems. 

Timed-release capsules-These dosage forms gradually release the active medication so that the total daily dosage may be administered in 1 to 3 doses. These products are not necessarily interchangeable. If patients are switched from one brand to another, closely monitor their theophylline serum levels. 

During imbibition of whole tea seeds (6 days) two purine alkaloids, caffeine and theobromine, did not decrease in the seed coats and there was no increase in the seeds. In parallel with and after the breaking seed coats there was a gradual release of caffeine from coats of germinating seeds. By contrast, when the seed was freed from the outer seed coat and soaked, imbibition of the seed required only two days and simultaneously caffeine was released from the inner seed coat. 

The pH is thus slowly raised in the solution by the gradual release of ammonia basic carbonates are precipitated. Although very uniform spherical particles are obtained (Figure 2), they do not have a homogenous cation distribution since upon the slow increase of pH, Cu is precipitated first as the nucleus of these particles, then Y (32). Ba can be precipitated only if large amounts of urea are used (31). Another procedure is to first precipitate Y Cu particles then disperse them in a solution containing Ba(NOs)2 and urea in order to, by the... 

Hard capsules are used for powdered drugs e.g. capsules ampicillin, tetracycline. In hard capsules, certain sustained released substance, which gradually release the drug in the respiratory tract (e.g. cap. theophylline). 

The limited penetration of topical corticosteroids can be overcome in certain clinical circumstances by the intralesional injection of relatively insoluble corticosteroids, eg, triamcinolone acetonide, triamcinolone diacetate, triamcinolone hexacetonide, and betamethasone acetate-phosphate. When these agents are injected into the lesion, measurable amounts remain in place and are gradually released for 3-4 weeks. This form of therapy is often effective for the lesions listed in Table 61-2 that are generally unresponsive to topical corticosteroids. The dosage of the triamcinolone salts should be limited to 1 mg per treatment site, ie, 0.1 mL of 10 mg/mL suspension, to decrease the incidence of local atrophy (see below). 

THC is optically active and the levorotatory form is 10 to 15 times more potent than the dextrorotatory. The therapeutic index (Tl) has been reported to be 40,000. Due to its lipophilicity, THC crosses the placental membrane and is stored in fat deposits in the body. In fact its pattern of appearance in the plasma is bimodal, that is, it shows up almost immediately after use to a certain extent and then reappears over a period of anywhere from 14 to 30 days as it is gradually released from fat stores and metabolized. The... 

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