PubMed · 8973757
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P A van Zwieten, G Mancia. 1996. Third generation calcium antagonists: further developments.. https://doi.org/10.3109/08037059609078078
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The twin-screw hot-melt extrusion process is useful for preparing solid dispersions which can improve the dissolution and absorption of drugs. The kneading paddle elements of the screws play an important role in changing the crystallinity and dissolution properties of a solid dispersion of kneaded nifedipine-hydroxypropylmethylcellulose phthalate (NP-HPMCP). After operating the machine, a small amount of kneaded material adhering to the screws was collected and its physicochemical properties examined. Samples from the kneading paddle with a twist angle of 60 degrees were transparent and exhibited super-saturation on dissolution testing. When the kneading paddle elements were detached from the screws and only the feed screw elements were operated, the physicochemical properties of the extruded material were significantly influenced by the operating conditions of the machine e.g. revolution rate of screws, and the amount of water added to the feed materials. Slow revolution of the screws and the addition of a suitable amount of water to the mixture increased the rate of drug dissolution, although no super-saturation occurred. As the kneading paddle elements can retain the mixture in the machine for a longer period under intense shear, desired solid dispersions can be prepared routinely irrespective of the operating conditions. Moreover, a capillary rheometer can be useful to predetermine the amount of water added and the temperature for the preparation of solid dispersions using a twin-screw extruder.
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A simple, rapid and sensitive high performance thin layer chromatographic method was developed and validated for the estimation of lacidipine. The sample preparation involved protein precipitation followed by an efficient solid phase extraction on C18 cartridge. The analytes were isolated from 1 ml of urine and recovered by pure ethyl acetate solution. The method employed TLC aluminium plate precoated with silica gel 60F254 as the stationary phase. The solvent system employed consists of toulene-ethyl acetate [6.5:3.5v/v]. This system gave a dense and compact spot of the drug at R(f) value of 0.45. The linear regression data for the calibration plots showed good linear relationship (r=0.999) over the concentration range 10-80 ng. Recovery studies were performed at two different levels. The recovery data reveals that the R.S.D. for intra-day and inter-day analysis at 10 ng was found to be 0.84 and 0.22%, respectively. The proposed method was found to be useful for the routine analysis of pharmaceuticals and pharmacokinetic studies in human urine samples.