Aspirin in suspension

The hydrolysis of aspirin in aqueous suspension is zero-order. Aspirin was suspended in an aqueous solution, which was maintained at pH 2.5. The amount of aspirin suspended initially was 70 g/L. After 2 weeks, a 5 ml aliquot of the suspension was withdrawn and found by analysis to contain 0.3375 g aspirin, (a) What is the rate constant for the hydrolysis of aspirin in suspension, expressed in g/L/day (b) How long will it take for 10% of the aspirin suspended initially to hydrolyze (c) After 50% of the aspirin suspended initially is hydrolyzed, how much additional time is required for 50% of the remaining aspirin to hydrolyze ... 

Degradation of aspirin in suspension has been reported to follow zero-order kinetics (Fig. 7).249... 

Figure 7. Time course of degradation of aspirin in suspension (pH 3.0), showing apparent zero-order behavior and a dependency on temperature but no dependency on particle size. Particle size , 60 mesh O, 100 mesh. (Reproduced from Ref. 249 with permission of the American Pharmaceutical Association.)...

Figure 92. Effect of grinding time on the degradation of aspirin in suspension at 40°C. o, Zero-order rate constant , solubility. (Reproduced from Ref. 414 with permission.)...

Stability and decomposition kinetics of aspirin both as a solid and in solution continue to be studied. The topochemical decomposition pattern of aspirin tablets has been explored.175 The degradation of aspirin in the presence of sodium carbonate and high humidity was studied by x-ray diffraction.176 The activation energy of decomposition by water vapor in the solid state was found to be 30 kcal/mol.177 The effect of common tablet excipients on aspirin in aqueous suspension was also studied.178... 

FIGURE 5.4 Hydrolysis of aspirin in an aqueous suspension at 34°C. [Graph reconstructed from data by K. C. James, J. Pharm. Pharmacol., 2, 363 (1958).]... 

Brockman MJ, Eiroa AM, Marcus AJ (1991) Inhibition of human platelet reactivity by endothelium-derived rehning fodorfiom human umbilical vein endothelial cells in suspension blockade of aggregation and secretion by an aspirin-insensitivemechanism. Blood 78 1033-1040. 

Studies of the pathophysiology of acute renal failure has classically considered both tubular and vascular mechanisms [227,228]. In vitro techniques isolating either the vascular or tubular components have been developed. For example, the use of isolated proximal tubules in suspension or in culture allows the study of tubular mechanisms of injury in the absence of vascular factors [229] [230]. There are both in vitro and in vivo models to study vascular injury in the kidney. In vitro models include the study of vascular smooth muscle cells or endothelial cells in culture. In this section, the in vivo methods to evaluate the renal micro-circulation will be discussed. This is of relevance as many nephrotoxins exert their deleterious effects through pharmacologic actions on the resistance vasculature with parenchymal injury occurring as a consequence of ischemia. In clinical practice nephrotoxins may cause prerenal azotemia as a result of increased renal vascular resistance. Nephrotoxins that cause acute renal failure on a vascular basis include prostaglandin inhibitors e.g. aspirin, non-steroidal anti-... 

S. S. Komblum and M. A. Zoglio, Pharmaceutical heterogeneous systems I. Hydrolysis of aspirin in combination with tablet lubricant in an aqueous suspension, J. Pharm. Sci. 56, 1569-1575(1967). 

Eight patients receiving 12 to 48 units of insulin zinc suspension daily required no insulin when they were treated for 2 to 3 weeks with aspirin in doses of 3.5 to 7.5 g daily, which were large enough to give maximum therapeutic serum salicylate levels of about 2.5 to 3.3 mmol/L. Six other patients were able to reduce their insulin requirements by between about 20and65%.2... 

Chinese Herbal Medicines. Many traditional Chinese medicines have been screened for radioprotective activity in experimental animals. In one study of more than a thousand Chinese herbs, a number of agents increased the survival rate of dogs exposed to a lethal dose of y-rays by 30—40%, and some symptoms of radiation injury were ameHorated. These effects are potentially related to stimulation of the hemopoietic and immune systems (130). Extracts of five Chinese dmg plants, as weU as aspirin, effectively protected mice exposed to 7.5—8.0 Gy (750—800 rad) of y-radiation, and increased survival rates by 8—50% (131). Several Chinese traditional medicines, adininistered ip before or after irradiation, protected against Hpid peroxidation in a variety of mouse tissues, including BM, Hver, and spleen, as weU as in mouse Hver microsomal suspensions irradiated in vitro (132). 

The degradation of aspirin by hydrolysis in an aqueous suspension was carried out and is represented in Figure 5.4. What is the apparent rate constant for the hydrolysis of the aqueous aspirin suspension What is the hydrolysis rate constant in an aqueous phase Assume the initial concentration is 0.21 mole/L. The solubility of aspirin is... 

The aqueous hydroxide extract contains aspirin as the sodium salt of the carboxylic acid. To the aqueous solution add 3M hydrochloric acid dropwise until the solution tests strongly acid to indicator paper, and then add two more drops of acid. This will give a suspension of white ace-tylsalicylic acid in the aqueous solution. It could be filtered off and recrystallized from boiling water, but this would entail losses in transfer. An easier procedure is to simply heat the aqueous solution that contains the precipitated aspirin and allow it to crystallize on slow cooling. 

Rainsford KD. Gastric mucosal ulceration induced in pigs by tablets but not suspensions or solutions of aspirin. / Pharm Pharmacol 1978 30 129-131. 

When absorption takes place rapidly, which is usual for conventional dosage forms, fca > kd, but when absorption takes place slowly and ka < k(j the flip-flop phenomenon occurs, whereby the rate of absorption controls the rate of elimination of the drug. This situation applies not only to sustained-release oral dosage forms administered to dogs, but also to phenylbutazone and meclofe-namic acid in horses, salicylate administered as an aspirin bolus to cattle and oral suspensions of benzimidazole anthelmintics in ruminant species. 

Exemplarily, for a typical fine chemical manufacturing process, the simplified process scheme of the aspirin production is presented in Figure 7.14. Acetylsali-cylic acid as produced by reaction of salicylic acid and acetic anhydride in a batch reactor is subjected to a cooling crystallization. The resulting suspension is transferred to a filter to remove the solvent and acetic acid formed as by-product. 

On the basis of IR and Raman spectroscopy (Table 5.2, Figure 5.12), which are relatively cheap, fast, and easy for technical operation and interpretation of data, and do not require sample dissolution methods, we presented the quantitative determination of the six binary mixtures with the studied cephalosporins in solid state, which was reported for the first time in the literature. The IR-LD analysis of oriented colloids as a liquid crystal suspension was applied for experimental IR band assignment and selection of appropriate bands for quantitative determination. This method gives additional supramolecular solid-state structural information at room temperature and atmospheric pressure. It also avoids the phase transition and guarantees the study of different forms without polymorph transitions. This approach has been applied recently for caffeine as a matrix compound and for studying the polymorphs of Paracetamol, Aspirin, Phenacetin , and Salophen. The spectroscopic data were... 

---