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This report describes zero-order approximation for metoclopramide hydrochloride sublingual tablet formulation. Effects of type and concentration of excipients on release were investigated. Study revealed that highest rate of dissolution was attained with crosspovidone and decreased in the order crosspovidone > sodium starch glycolate > ac-di-sol. All formulations demonstrated flush release, except the one containing 10% crosspovidone where a lag time of 0.5 min. was depicted. Increasing the concentration of crosspovidone from 5 to 10% gave the same half-life, whereas kinetics of release changed to zero order. Differential scanning colorimetry and infrared spectroscopy did not reveal any sign of physical or chemical interaction between drug and crosspovidone. In order to study the alignment of polymeric network inside tablet matrix, scanning electron microscopy was performed on the tablet and its cross-section. Matrix with 10% crosspovidone showed higher density of interconnections extending to the interior of core enabling fast and constant release. Hence physicochemical characteristics of crosspovidone could be tailored by varying its concentration, in a way that provided a porous matrix with tight arrangement of polymeric chains, resembling to an assemblage of cylinders with constant apertures, from which zero-order release was approached.

ZH501 strain of Rift valley fever virus (RVFV) was originally isolated from a human patient during the outbreak of 1977 in Egypt. This virus strain was used since 1980 for preparation of an inactivated RVF vaccine at Veterinary Serum and Vaccine Research Institute (VSVRI), Egypt. Two subpopulations of ZH501 with a single nucleotide polymorphism (A/G) at nucleotide position 847 of Gn gene of M segment have been described. This nucleotide substitution affected signifcantly RVFV virulence in the mouse model. In this report, the genetic makeup of the Gn gene of ZH501-VRVSI vaccine virus stock was analyzed for verifcation of its safety and stability. Plaque assay of the vaccine stock virus revealed the presence of two populations that produced different plaque forms. The viruses that developed large plaques resembling those produced by the virulent virus strains were isolated for genetic analysis. Comparison of the Gn gene nucleotide sequence of the isolated viruses with those of the wild-type ZH501 and other reference strains identifed fve nucleotide substitutions, of which three are capable to induce amino acid changes in the mature protein. Protean analysis suggested a potential change in the three dimensional structure of the Gn protein in relation to the parent strain. The results of this study throw light on the changes occurred in the master seed virus used for preparation of RVFV vaccine in Egypt. Further studies focusing on the other gene segments of
ZH501-VSVRI are required to conclude is it still the best choice for vaccination against RVF in Egypt.