Dissolution rate of salicylic acid

Fig. 17 Effect of starch content of granules on dissolution rate of salicylic acid contained in compressed tablets. Q, 5% . 10% x, 20% starch in granules. (From Ref. 22.).

Figure 5 Dissolution rates of salicylic acid-benzoic acid mixtures. ( ) Benzoic acid from melt (O) salicylic acid from melt (A) salicylic acid from mechanical mix ( ) Benzoic acid from mechanical mix. (From Ref. 19.)... 

BiUany, M. R., and Richards, J. H. Batch variation of magnesium stearate and its effect on the dissolution rate of salicylic acid from solid dosage forms. Drug. Dev. Ind. Pharm. 8 497-511, 1982. 

Underwood 1W, Cadwallader DE. Influence of various starches on dissolution rate of salicylic acid from tablets. / Pharm Sci 1972 61 239-243. 

In yet another important study. Levy et al. (2) studied the effect of the granule size on the dissolution rate of salicylic acid tablets and found that the dissolution rate increased with a decrease in the granule size the increase in dissolution rate, however, was not proportional to the increase in the apparent surface area of the granules. Furthermore, it was also reported that the dissolution rate decreased significantly with the increase in the age of the granules. 

Serajuddin, A.T.M. Jarowski, C.I. Effect of diffusion layer 54. pH and solubility on the dissolution rate of pharmaceutical acids and their sodium salts. II. Salicylic acid, theophylline and benzoic acid. J. Pharm. Sci. 1985, 74 (2), 148-154. 55. 

The effect of organic anions on silicates other than quartz and feldspar has also been investigated. Dissolution rates of kaolinite are enhanced more by oxalate than salicylate, while malonate and phthalate show little effect (CarroU-Webb and Walther, 1988 Chin and Mills, 1991 Wieland and Stumm, 1992). Dissolution of hornblende is accelerated at pH 4 in the presence of organic acids at 2.5 mM rate enhancement was observed... 

Figure 7.4 Plot of dissolution rate constants (kgs x 10 ) of salicylic acid against concentration of polysorbate 20 at several pH values JpH 10, OpH 2.0, pH 3.0, DpH 4.0. From Rees and Collett [10] with permission.

However, both Collett and Rees [19] and Gibaildi et al. [25] find that dissolution rate is proportional to the effective diffusion coefficient raised to the power 0.5 to 1.0, thus placing in some doubt the diffusion coefficients of salicylic acid calculated assuming Equation 7.4 to hold [20]. The lack of agreement between the dissolution data and the predictions of Equation... 

Figure 5. Dependence of rate of dissolution of 5pM Y-FeOOH in pH 4.0, 0.01M NaCl on concentration of a) tartaric acid, and b) salicylic acid. Fitted parameters obtained for rectangular hyperbolic model are given. Light source mercury arc lamp with 365nm band-pass filtering.

The apparatus suitability test described in USP General Chapter <711> Dissolution is equivalent to a performance qualification.5 The determination of suitability of a test assembly to perform dissolution testing must include conformance to the dimensions and tolerances of the apparatus. In addition, the critical test parameters that have to be monitored periodically include volume and temperature of the dissolution medium, rotation speed (Apparatuses 1 and 2), dip rate (Apparatus 3), and flow rate of medium (Apparatus 4). This test requires that the USP Calibrator Tablets (now known as Performance Verification Standard Tablets) be tested the dissolution results must be within the ranges stated in the certificate of the calibrator tablets. The performance verification standard tablets include USP Chlorpheniramine Maleate Extended-Release Tablets RS, USP Prednisone Tablets RS, and USP Salicylic Acid Tablets RS. 

Except for theophyllin, the solubilities are similar at a dissolution temperature (Td) and a dissolution pressure (Pd) of 65°C and 250bar, respectively, the mole fractions are of 2.5e-4 for anthracene, 5e-4 for caffeine and 6.5e-4 for salicylic acid. Theophyllin is an order of magnitude lower, with a value of 0.2e-4. The mole fractions allow one to estimate the maximum production rate for the experimental set up. Assuming a recovery of produced particles of 100%, and no dilution required for processing, the production rates are 1.0, 1.2, 0.5 and 0.04 g/h for caffeine, salicylic acid, anthracene and theophyllin, respectively (conditions Pd = 220bar, Td=65°C, capillary =1.5cm x 75pm flow rate of liquid C02=11.2ml/min)... 

Quantitative data on the rate of consumption of pfa are few and somewhat variable. Those based on differences between the CH contents of pure Portland and pfa cements are suspect, because the calculation involves the effects of pfa substitution both on the rate of consumption of the clinker phases and on the compositions of the products, which are not fully understood. Unreacted pfa has been directly determined by dissolution of the other phases with HCl (C43) or with salicylic acid in methanol followed by HCl (T44), chemical separation of the residual pfa followed by QXDA determination of its content of crystalline phases (D12) and a trimethylsily-lation method (U19). A method based on EDTA extraction was found unsatisfactory (L46). 

Calibrators are used to show deficiencies in the equipment, for example, chain looseness, tilting of stirrer motor, excessive vibration, or misalignment of the flasks with the stirrers. Non-disintegrating calibrators are composed of 300 mg salicylic acid, whereas disintegrating calibrators contain 10 mg prednisone. The dissolution rates obtained from the calibrants should fall within established ranges at both 50 and 100 rpm. 

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