[Characterization of the resistance to combinations of beta lactams and inhibitors of beta-lactamases in Escherichia coli. Effect of the type and amount of beta-lactamase production]. / Caracterización de la resistencia a asociaciones de betalactámicos e inhibidores de betalactamasas en Escherichia coli. Influencia del tipo y nivel de producción de betalactamasas.

BACKGROUND: The aim of this study was to characterize resistance of Escherichia coli in our environment to four associations of beta-lactams and beta-lactamase inhibitors (beta Lac) studying the influence of the type and level of beta Lac production. METHODS: The minimum inhibitory concentration (MIC) to ampicillin/sulbactam (A/S), amoxycillin/clavulanic acid (A/C), ticarcillin/clavulanic acid (T/C) and piperacillin/tazobactam (P/T) assessed was in 245 strains of E. coli resistant to ampicillin, consecutively isolated in our laboratory from September 1995 to March 1996. The beta Lac produced by these isolates were identified by isoelectrofocusing and spectrophotometrically quantified. RESULTS: The sensitivity to A/S, A/C, T/C and P/T was of 9.4, 86.9, 64.5 and 89.4%, respectively. The strains with only one beta Lac which cofocused with TEM-1 were the most frequent (215/245), followed by those producing a cofocusing enzyme with SHV-1 (7/245). A significant correlation was observed between beta Lact activity of the 215 TEM-1 strains and their MIC at A/S (r = 0.53; p < 0.001), A/C (r = 0.46; p < 0.001), T/TC (r = 0.58; p < 0.001), and P/T (r = 0.42; p < 0.001). The comparison between enzyme activity of the isolates of the different categories of susceptibility showed significant differences (p < 0.05) for the four associations studied. CONCLUSION: TEM-1 production is the main cause of resistance to beta-lactams in E. coli in our environment. The inhibitory efficacy of sulbactam, clavulanic acid and tazobactam over TEM-1 is inversely proportional to the amounts of enzyme produced. The high rate of resistance to A/S and T/C E. coli presents in our environment is mainly due to a hyperproduction of TEM-1.

Spectrophotometric determination of dihydralazine in pharmaceuticals after derivatization with 2-hydroxy-1-naphthaldehyde.

A sensitive and selective colorimetric assay has been developed for the determination of dihydralazine. The method is based on the interaction of dihydralazine with an ethanolic solution of 2-hydroxy-1-naphthaldehyde to yield a water-insoluble yellow product, 1,4-bis[(2-hydroxy-1-naphthyl)methylene hydrazine]phthazine. This colour can be quantified spectrophotometrically at 420 nm. The calibration curve was linear between 0.4 and 8 micrograms ml-1 of dihydralazine. The molar absorptivity at 420 nm is 24000 l mol-1 cm-1. The method was successfully applied to the determination of dihydralazine in mixtures containing other drugs (reserpine, hydrochlorothiazide, oxprenolol, xanthinol, rutoside, chlorthalidone and bietaserpine).

Spectrophotometric determination of hydralazine with 2-hydroxy-1-naphthaldehyde in pharmaceuticals.

A new extraction-spectrophotometric method for the determination of hydralazine, based on its reaction with 2-hydroxy-1-naphthaldehyde at 25 degrees C, is described. The calibration curve was linear between 0.4 and 6 mg/mL of hydralazine. The molar absorbtivity of the product at 408 nm is 40,900 L.mol-1.cm-1. The method described was applied to the analysis of hydralazine in pharmaceutical preparations containing reserpine, hydrochlorothiazide, bendrofluorthiazine, propranolol, and other substances. The agreement with the U.S.P. XXI method was satisfactory for tablets and injections, but not for pellets.