Parameters dissolution

Diffusive dissolution of MgO-rich olivine and diffusion profiles MgO is the principal equilibrium-determining component and its diffusion behavior is treated as effective binary. Consider the dissolution of an olivine crystal (Fo90, containing 49.5 wt% MgO) in an andesitic melt (containing 3.96 wt% MgO) at 1285°C and 550 MPa (exp 212 of Zhang et al. 1989). The density of olivine is 3198 kg/m, and that of the initial melt is 2632 kg/m. Hence, the density ratio is 1.215. To estimate the dissolution parameter a, it is necessary to know the interface melt... 

In previous work, the formula used were optimized by direct compression [13]. The area under the dissolution curve was optimized and validated by a composite design. However, the formulation gave poor powder flow as well as variability in the dissolution parameters. Thus the double compression process was investigated in order to change the powder into solid aggregates and therefore to enhance homogeneity, density and powder flow in addition it was expected that this process would reduce the variability between tablets. 

In conclusion, the incorporation of 50% magnesium stearate and talc before precompression and the other 50% before the final compression improves the compression behaviour. At the same time, it decreases the coefficients of variation of UPF the weight of the tablet and dissolution parameters. From these results, the process from experiment was chosen for the experimental designs. 

From the models, when X2, and X4 decrease, the dissolution parameters increase. This can be explained by the hydrophobic effect of the ethylcellulose (X4). Furthermore, an increased effective drug surface area occurs when the particle size range and the UPF at the final compression are at minimal levels and an increase in dissolution rate occurs. The area under the dissolution curve is far above the optimum value (713% h). Another experimental design must be explored. 

The area under the dissolution curve (AUC=T6), was chosen as the major response to be optimized. Nevertheless, the results showed that it is necessary to study several properties to define the best formulation adequate powder flow, compression behaviour and particularly, a minimal variability of the dissolution parameters [3]. It was noted that good powder flow rate is not always related to an adequate compression behaviour [4]. 

The variability of the porosity parameters may be used to differentiate the processes. It also explains the variability of the dissolution parameters because of the same order of variation (CV) ... 

A Level C IVIVC establishes a single point relationship between a dissolution parameter, for example, t5o%, percent dissolved in 4 hours and a pharmacokinetic parameter (e.g., AUC, C ax. I max)- A Level C correlation does not reflect the complete shape of the plasma concentration time curve, which is the critical factor that defines the performance of ER products. 

Table I. Experimental and Theoretical Data of Dissolution Parameters...

K = dissolution parameter of the active drug inside the matrix... 

In this section the controlled release delivery systems applying dissolution as the major release mechanism are discussed. Since many of these systems actually apply to both the concepts of dissolution and diffusion in the design, only the dissolution parameters affecting the release profiles and the release rates of these systems are analyzed. 

As shown above, if the initial dissolutional parameters are known (mean annual temperature, type of dissolution system), then the [Ca ] of the cave dripwaters can be estimated Drake and Wigley (1975) demonstrated an empirical correlation between regional temperatures and spring water /7CO2, and thus CO2. The next section summarises the controls on precipitation and translates them into growth rates. 

The mean in vitro dissolution time is compared to either the mean residence time or the mean in vivo dissolution time. Level B correlation, like Level A correlation, uses all of the in vitro and in vivo data but is not considered to be a point-to-point correlation and does not uniquely reflect the actual in vivo plasma level curve, since several different in vivo plasma level-time curves will produce similar residence times. A Level C correlation is the weakest IVIVC and establishes a single point relationship between a dissolution parameter (e.g., time for 50% of drug to dissolve, or percent drug dissolved in two hours, etc.) and a pharmacokinetic parameter (e.g., AUC, Cmax, Tmax). Level C correlation does not reflect the complete shape of the plasma drug concentration-time curve of dissolution profile. 

Fig. 3 Relationship between the dissolution parameter tgo-io of effervescent enteric tablets of levodopa and the amount of sodium bicarbonate formulated in the tablet. The number of strokes was fixed at 5/min and the pH was 7.5. Key ( ) = uncoated tablet (O) = enteric tablet. (From Ref. "l)...

Two additional hydrofluoric acid methods have been reported (1,2), and are similar to that described above. The method of Hughes et al. has also been the subject of two comparative studies relevant to the analysis of ceramics (2,31). Techniques that retain silicon have been discussed (1,2) and involve either fusion with lithium metaborate [or sodium carbonate (2)] or high pressure dissolution in a PTFE bomb. An alternative high pressure method, developed by Price and Whiteside (32), was evaluated in the course of this investigation but was found to be unreliable for stained glass of medieval composition in many experiments dissolution was incomplete. Attempts to modify the procedure by varying the prescribed dissolution parameters produced insufficiently consistent results although superior conditions were established (Table I). 

Annexures 7A and 7B call for a summary of the final product specifications, and where applicable some of the above comment is also relevant here. The product must be specified fully, even including parameters that are not routinely tested (e.g., a disintegration specification in addition to a dissolution parameter). If release and stability specifications differ, they must be clearly distinguished. All the stability parameters must correspond with those reflected in Annexure 10. 

TABLE 5.3. Typical Energetic and Dissolution Parameters of the Electrolytic Dissolution Process for Different Timgsten Scraps [5.30]... 

A level C correlation establishes a relationship between a dissolution parameter such as the amount of drug dissolved at a certain time and a pharmacokinetic (PK)... 

Celecoxib HP-(3-CD HPMC Physical mixing, co-evaporation Water Increase in value of stability constant of complex on addition of HPMC to complexation medium along with brief autoclaving, which was reflected by better dissolution parameters of ternary complex than the drug alone [68]... 

Table 2 Wetting dynamic contact angle values of white beeswax coated potassium chloride microcapsules with different core-to-wall ratios and dissolution parameters of the Weibull distribution function (the medium for the wetting and dissolution measurements was distilled water)...

Figure 3 shows the dissolution kinetics and Table 4 summarises the dissolution parameters derived from the rapid and slow dissolution phases by fitting equation 2 to the experimental data using a non linear least squares fitting routine based on the Levenberg Marquardt method. Table 5 summarises the radiochemistry results with imcertainties. 

Some of these clearance mechanisms compete with others, such as particle uptake by phagocytes versus epithelial cells and phagocyte migrational parameters. Others run parallel, for instance, particle dissolution parameters are independent of transport parameters no matter whether the latter are associated with free particle transport or mediated by phagocytes. The latter has an important consequence the clearance pathway of particle dissolution and subsequent uptake of dissolved material by blood (absorption) is independent of particle transport pathways inside and out of the peripheral lungs. This concept was challenged by ICRP-66 (2) and was supported by several studies. Given this assumption, the fractional clearance rate CL(t) of Eq. (2) is the sum of the dissolution and uptake rate S(t) and particle transport rate M(t) ... 

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