Hollow core's inner surface coating in a photonic bandgap fibre (PBGF) is investigated by means of finite element method. The coat material and thickness-dependence dispersion curve and group velocity dispersion are numerically studied. The coating with materials of low index or small thickness will rise up the dispersion curve but will not induce surface modes. However, coating with materials of high index or big coat thickness will induce surface modes and avoided-crossings. By varying coat material's refractive index and thickness, the appearances of surface modes and avoided-crossings can be changed. It is found that the avoided-crossing can enormously enlarge the negative dispersion which can find applications in dispersion compensation. We numerically achieve a negative dispersion as large as −21416.15 ps/nm/km. The results give a physical insight into the propagation properties of PBGFs with the hollow core coated by a layer of material and are of crucial significance in the applications of PBGF coating.

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A new ready-to-use medicinal form -granules containing isoniazid and pyridoxine hydrochloride (0.15 and 0.015 g per gram of granules, respectively) -has been recently developed. An HPLC technique for the qualitative and quantitative analysis of the new preparation is described. The analyses are carried out using a Millihrom-2 chromatograph equipped with a UV detector and a KAKh 4-64-3 column filled with Separon C 18 . The column is eluted with an acetonitrile -0.5% aqueous sodium dihydrophosphate solution (60:40, adjusted with orthophosphoric acid at pH 2.5 -3.0) at a flow rate of 50 ml/min. The detection is carried out at 280 nm. The relative error of determination does not exceed ± 1.1% for isoniazid and ± 4.1% for pyridoxine hydrochloride.

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Corticosteroids, especially dexamethasone (DM), play an important role in eye therapy [I]. DM is used in the form of a 0.1% suspension or 0.05-0.1% solutions. Although DM is now produced in Russia, no domestic ophthalmologic preparations have been developed until recently.The purpose of this work was to prepare DM-based eye drops using the commercially available parent compound and domestic auxiliary substances. In particular, for DM dissolution we used 2-hydroxypropyl-13-cyclodextrin (HPCD) known to form inclusion complexes with steroidal compounds [2]. EXPERIMENTAL CHEMICAL PARTCDM, mote/liter 0.07The experiments were performed with DM obtained from the Akrikhin chemico-pharmaceutical plant (Akrikhin jointstock company) and HPCD (Novodeks Ltd., Ufa) produced according to State Technical Conditions TU 406K-H2100-002 -92 with 3.7 hydroxyl groups per macrocycle.The effect of HPCD on DM solubility was studied using a series of HPCD solutions with concentrations ranging from 5 to 100 mg/ml at a 5 mg/ml step.To 100 ml of an HPCD solution was added 50 mg DM and the mixture was treated in a shaker for 1 rain and allowed to stand for 1 day, after which the DM content in the supernatant liquid was determined by spectrophotometry at L = 246 nm (~ = 440). Figure 1 shows the results of averaging over three parallel determinations. As seen from these data, the solubility of DM in a 100mg/ml HPCD solution increases by a factor of 170 compared to the DM solubility in water. The dependence of the DM solubility on the HPCD concentration in water belongs to the type A [3], which is evidence of the DM-HPCD interaction with the formation of a water-soluble complex. No deviations from the linear de-State Pharmaceutical Academy, Pyatigorsk, Russia. pendence were observed in the entire HPCD concentration range studied (type AL ), which is indicative of considerable HPCD solubilization and the high solubility of the HPCD-DM compound formed.These results indicate that HPCD can be used for the preparation of DM solutions, the optimum HPCD concentration being 4%. Because the DM solutions are intended for use in ophthalmology, there arises an important question concerning the stability of both DM and HPCD in solution. To our knowledge, no data were reported on HPCD stability in aqueous solutions. For this reason, we have studied the be-160 0.06 0.05 0.04 0.03 0.02 0.0l 0. '02 0104 0106

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