Coulometric titration of urea with electrogenerated hypobromite.

A definitive method is described for the indirect assay of several tens of milligrams of urea by coulometric titration. Urea was decomposed in concentrated sulfuric acid using a Kjeldahl flask. Subsequently, the formed ammonium ion was titrated with electrogenerated hypobromite ion in a sodium bromide-sodium tetraborate medium of pH 8.6, with amperometric end-point detection. Parameters affecting the pretreatment procedure were evaluated. The optimized conditions included the heating of 2 g of urea at around 300°C for 2 h with 10 cm(3) of sulfuric acid. Under the proposed conditions, the assay value with expanded uncertainty (k = 2), 99.870 ± 0.026%, agreed well with the certified value of NIST SRM 912a urea, 99.9 ± 0.1%.

Preparation and evaluation of novel directly-compressed fast-disintegrating furosemide tablets with sucrose stearic acid ester.

Fast-disintegrating tablets of furosemide (FS) were prepared by the novel direct compression method. FS, microcrystalline cellulose (MC), croscarmellose sodium (CC), xylitol (XL) and sucrose stearic acid esters (SSEs) with an hydrophilic-lipophilic balance (HLB) of 16, 15 and 11, named S1670, S1570 and S1170, were used. An FS/SSE/MC mixed powder was obtained by solvent evaporation of a suspension of MC in ethanol solution containing FS and SSE, and the resultant mixed powder was mixed with CC and XL, and directly compressed. The tablets with hardness of more than 40 N and disintegration time of less than 20 s were obtained at the addition of SSE at 0--0.5% (w/w). A tablet with S1670 at 0.1% (w/w), named TA2, dissolved faster than a commercial FS tablet, Lasix. TA2 tended to show higher plasma concentration than Lasix after intragastric administration to rats. It was demonstrated that the present direct compression using homogeneous FS/S1670/MC powder mixture could give an excellent fast-disintegrating tablet of FS.

Development of novel fast-disintegrating tablets by direct compression using sucrose stearic acid ester as a disintegration-accelerating agent.

It was attempted to produce novel furosemide (FS) fast-disintegrating tablets by direct compression. The combination of FS, microcrystalline cellulose, croscarmellose sodium and xylitol was used as the basic formulation, and sucrose stearic acid ester (SSE) was chosen as an additional additive. The tablets with SSE were prepared by the simple addition of SSE, using a lyophilized mixture of FS and SSE or using a FS/SSE mixture obtained by evaporation of their ethanol solution. Only the tablets, produced using the FS/SSE mixture obtained by organic solvent (ethanol) evaporation, showed hardness of more than 30 N and a disintegration time of less than 20 s, which were the properties suitable for fast-disintegrating tablets. These properties were considered to result from well-mixed and fine-powdered SSE and FS.