75511-23-8Relevant articles and documents
Hydrolysis mechanisms for indomethacin and acemethacin in perchloric acid
Garcia,Hoyuelos,Ibeas,Leal
, p. 3718 - 3726 (2007/10/03)
The acid-catalyzed hydrolysis reactions of the antiinflammatory drugs indomethacin and acemethacin were investigated at 25.0 °C in a number of strongly concentrated perchloric acid media. The reaction rates were evaluated by UV measurements, and the intermediate species were detected by UV-vis, 1H NMR, 13C NMR, and mass spectroscopy measurements. A switchover from an A-2 to an A-1 mechanism as a function of the medium acidity is reported for the acid-catalyzed hydrolyses of the amide group of both indomethacin and acemethacin. In the A-2 hydrolysis, two water molecules are involved in the rate-determining step. An analysis of the kinetic data collected for acemethacin by the different techniques used reveals a complex mechanism, indomethacin being a metabolite intermediate species in the hydrolysis of acemethacin. The rate constants for the hydrolysis of the acemethacin ester group were considerably larger compared to those of the amide group.
Effect of Liposomes on the Rate of Alkaline Hydrolysis of Indomethacin and Acemetacin
Matos, C.,Chaimovich, H.,Lima, J. L. F. C.,Cuccovia, I. M.,Reis, S.
, p. 298 - 309 (2007/10/03)
The anti-inflammatory, analgesic, and antipyretic drugs indomethacin (INDO) and acemetacin (ACE), extensively used for the treatment of diseases of degenerative or inflammatory character, exhibit marked gastric irritant action, have low water solubility at neutral pH, and decompose in alkali. Alternative formulations are being investigated to obtain products with lower toxicity and higher stability. Here we examine the effect of liposome charge on the rate of alkaline decomposition of INDO and ACE using micelles as reference. Binding of ACE and INDO to zwitterionic hexadecylphosphocholine (HDPC) micelles and phosphatidylcholine (PC) liposomes was analyzed using a two-phase separation model to quantify the effect of these aggregates on the rate of alkaline degradation. The substrate association constants to HDPC micelles were 1335 and 2192 M-1 for INDO and ACE, respectively, whereas the corresponding values for PC vesicles were 612 and 3050 M-1. The difference was attributed to the additional hydrophobicity of ACE. The inhibitory effect of HDPC micelles and PC vesicles was quantified by calculating the ratio between the rate constants in water (kw) and in the aggregate (km). The values of the kw/km ratios for INDO and ACE in HDPC micelles were, respectively, 80 and 42, and in PC liposomes these ratios were 21 and 3.7, respectively. Positively charged micelles of hexadecyltrimethylammonium chloride (CTAC) and vesicles containing varying proportions of dioctadecyldimethylammonium chloride (DODAC) and PC increase the rate of INDO and ACE alkaline decomposition. Vesicle effects were very sensitive to the DODAC/PC ratio, with rates increasing with the proportion of DODAC. The data were analyzed quantitatively using a pseudophase model with explicit consideration of ion exchange. The calculated second-order rate constants in micelles and vesicles were lower than that in water. The charge density in the liposome necessary to increase the entrapment efficiency and decrease drug decomposition can be modulated, by judicious choice of pH and ionic strength. These manipulations can lead to more stable formulation with increased efficiency in drug entrapment and controlled effects on drug stability.
