Dissolution rate salts

The physicochemical factors affecting the absorption are lipid solubility, dissolution rate, salt from complexation, viscosity and drug stability in the GIT. 

Salt Formation. Salt formulation is one of the most commonly used approaches to deal with Class II compounds as a way to enhance drug solubility and dissolution rate. Salt selection largely depends on piiTa. It is generally accepted that a minimum difference of 3 units between the value of the group and... 

The formation of deposits on platinised anodes can cause anode degradationThus dissolved impurities present in water which are liable to oxidation to insoluble oxides, namely Mn, Fe, Pb and Sn, can have a detrimental effect on anode life. In the case of MnOj films it has been stated that MnOj may alter the relative proportions of Cl, and O, produced and thus increase the Pt dissolution rate Fe salts may be incorporated into the TiO, oxide film and decrease the breakdown potential or form thick sludgy deposits. The latter may limit electrolyte access and iead to the development of localised acidity, at concentrations sufficient to attack the underlying substrate . 

Nevertheless, Ta5+ and Nb5+ interact with aqueous media containing fluorine ions, such as solutions of hydrofluoric acid. On the other hand, as was clearly shown by Majima et al. [448 - 450], the increased hydrogen ion activity can also significantly enhance the dissolution rate of oxides. The activity of hydrogen ions can be increased by the addition of mineral salts or mineral acids to the solution. 

Thus, as the pH increases, the dissolution rate of a weak base decreases. Referring to Table 2, we can see that, for the weak acid tolbutamide, the dissolution rate increases as pH is increased, as predicted by Eq. (3). Additionally, for the weak base tetracycline, as predicted by Eq. (4), the dissolution rate decreases as pH is increased. Thus far, the more rapid dissolution of the salt forms of these drugs and the direction of change of the dissolution rate with pH have been accounted for with Eqs. (1) to (4). However, there are six possible dissolution rate... 

The comparison of I —> N and N —> I may also be explained by the buffered pH in the diffusion layer and leads to an interesting comparison between a process under kinetic control versus one under thermodynamic control. Because the bulk solution in process N —> I favors formation of the ionized species, a much larger quantity of drug could be dissolved in the N —> I solvent if the dissolution process were allowed to reach equilibrium. However, the dissolution rate will be controlled by the solubility in the diffusion layer accordingly, faster dissolution of the salt in the buffered diffusion layer (process I—>N) would be expected. In comparing N—>1 and N —> N, or I —> N and I —> I, the pH of the diffusion layer is identical in each set, and the differences in dissolution rate must be explained either by the size of the diffusion layer or by the concentration gradient of drug between the diffusion and the bulk solution. It is probably safe to assume that a diffusion layer at a different pH than that of the bulk solution is thinner than a diffusion layer at the same pH because of the acid-base interaction at the interface. In addition, when the bulk solution is at a different pH than that of the diffusion layer, the bulk solution will act as a sink and Cg can be eliminated from Eqs. (1), (3), and (4). Both a decrease in the h and Cg terms in Eqs. (1), (3), and (4) favor faster dissolution in processes N —> I and I —> N as opposed to N —> N and I —> I, respectively. 

E. Nelson, Comparative dissolution rates of weak acids and their sodium salts, J. Am. Pharm. Assoc. Sci. Ed., 47, 297-299 (1958). 

This paper presents new data on dissolution kinetics. The effects of alkali concentration, size of the cation, and salt addition were studied. The influence of segmental mobility on dissolution was elucidated by measuring the temperature coefficients of the dissolution rates. Experiments were also carried out to study the relation between the chemical structure of a polymeric Inhibitor and Its effectiveness 1n retarding dissolution. Based on these results,... 

Effect of Added Salt. It 1s well known that the presence of salt promotes dissolution (1.31. For a fixed NaOH concentration, the dissolution rates of both p-Cl-PHMP and PBPh-1 were found to increase... 

The effect of added salt on dissolution rate 1s not completely understood at present. A possible explanation of the plateau value 1s that the solubility of the salt in the solid reaches a limiting value at high concentrations. But additional studies are needed to arrive at a quantitative understanding of the observed decreases in CQ and n when salt 1s present. 

In silico models should also be used with care when it comes to predicting the absorption properties of salts and bases with low solubility in the intestinal fluids. All models use the thermodynamic solubility to calculate the dissolution rate and the saturation solubility in the different parts in the GI tract. However,... 

Some of the current methods of increasing dissolution rates of drugs are particle size reduction, salt formation, and development of the optimized delivery systems, such as solid dispersion, soft gelatin encapsulation, etc. 

Another major ion chromatography application is the analysis of active ingredient counterions. Frequently, drug substances are formulated as salts in order to achieve specific pharmaceutical properties (such as improved solubility or control of dissolution rate). The analysis of... 

It has been shown that polymers with free phthalic acid groups dissolve much faster and at a lower pH than those esterified with acrylic or methacrylic groups. The presence of plasticizer and the nature of the salts in the dissolution medium influence the dissolution rate [62],... 

In summary, the lag time of drug release may be controlled by the rate at which water penetrates through the coating or shell, the rate of fluid absorption of the polymer layer, the osmotic activity of salts and osmopolymers, the erosion and dissolution rate of the polymer layers and the thickness of the layers or coatings. 

In vivo results correspond quite well to those of the in vitro experiments although the effect of a basic additive seems to be greater in vivo. It is possible to increase the dissolution rate of PVM-MA esters in tear fluid by adding disodium phosphate or possibly other basic salts to the matrices. With basic additives it may be possible to modify drug release and polymer dissolution also in the case of other polyacids. 

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