Preparation and evaluation of pregelatinized plectranthus edulis (ethiopian potato) starch as an alternative direct compression excipient in paracetamol tablet formulations
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2018-05
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Abstract
Plectranthus edulis (Vatke) (Ethiopian potato) is an indigenous annual tuber crop which belongs to the family Lamiaceae. It is a diploid dicotyledonous plant with a height up to 150 cm. It has the potential of being used as an alternative source of starch for various applications in pharmaceutical, food, paper, and textile industry. As native starches are weak structurally and functionally, there is a need to increase their functionality through modification. Among the various starch modification techniques, physical methods have received more attention since they are chemical free and somewhat easier than the other methods. The aim of the study was to prepare and characterize pregelatinized Plectranthus edulis starch and evaluate its functionality as a direct compression excipient in tablet formulations. Starch extraction was carried out from the tubers of Plectranthus edulis using 0.075% (w/v) of sodium metabisulphite. The native Plectranthus edulis starch was physically modified by pregelatinization at different conditions. The pregelatinized Plectranthus edulis starch, prepared at optimum conditions (starch to water ratio of 1:3, at 65 oC for 5 min), was selected for direct compression studies as it had the best powder compaction and flow properties among the fifteen tested pregelatinized Plectranthus edulis starch products. This pregelatinized Plectranthus edulis starch product was compared against Starch 1500 and the native Plectranthus edulis starch for physicochemical characterization. To investigate the effect of lubricant concentrations on post-compaction properties of the starch products, lubricant sensitivity test was conducted for native Plectranthus edulis starch, pregelatinized Plectranthus edulis starch and Starch 1500® by preparing tablets at different magnesium stearate concentrations (0%, 0.25%, 0.5%, 0.75%, 1%, 1.5%, and 2%). The tablets were tested for weight variation, friability, crushing strength, tensile strength and disintegration time. Dilution potentials of pregelatinized Plectranthus edulis starch and Starch 1500 were determined by assessing friability, crushing strength, tensile strength and other parameters in tablet formulations containing various paracetamol concentrations (20%, 30%, 40% and 50% (w/w)).The X-ray diffractogram (XRD) of the pregelatinized Plectranthus edulis starch indicates that the pregelatinization process decreased the crystallinity of the starch. The major peaks that were observed in the XRD of native Plectranthus edulis starch disappeared following pregelatinization. Nonetheless, there was no total loss of crystallinity as indicated by the presence of a peak at 17.2o 2 in the XRD of pregelatinized Plectranthus edulis starch. The bulk density was found to increase from 0.6 0.01 g/ml to 0.72 0.01 g/ml following pregelatinization. The Hausner ratio and Carr‘s index of pregelatinized Plectranthus edulis starch (1.15 ± 0.02 and 13.25 ± 1.21, respectively) and Starch1500® (1.21 ± 0.02 and 17.92 ± 0.72, respectively) were significantly lower than the native Plectranthus edulis starch (1.40 ± 0.03 and 28.56 ± 1.77, respectively) (P < 0.05), suggesting the former has got better flowability than the native starch. The native Plectranthus edulis starch did not flow through the funnel but after modification the starch product was found to be a free flowing powder with 20.08 ± 1.01° angles of repose and 6.97 ± 0.2 g/sec flow rate. Compacts of native Plectranthus edulis starch were too soft and friable across the different lubricant concentrations and hence it was not included in all of the post-compaction studies. Pregelatinized Plectranthus edulis starch was able to accommodate 0.5% magnesium stearate with tablet hardness and friability value of 75.8 ± 3.67 N and 0.74 ± 0.01%, respectively. Compacts of Starch 1500, however, were acceptably hard (> 60 N) up to 0.25% of magnesium stearate concentration indicating pregelatinized Plectranthus edulis starch was found to be less lubricant sensitive. Both pregelatinized Plectranthus edulis starch and Starch 1500 were able to accommodate up to 30% of the active pharmaceutical ingredient (API) with crushing strength and friability values of (65.34 ± 3.28 N and 0.75 2.09%) and (61.32 4.12 N and 0.98 3.11), respectively. At all levels of paracetamol powder, tablets of Starch 1500 exhibited less crushing strength and were more friable as compared to those of pregelatinized Plectranthus edulis starch (P < 0.05). Disintegration and dissolution tests of acceptable direct compression paracetamol tablets for both starch products met the pharmacopoeial requirements (BP, 2009; USP 30-NF 25, 2007).
In general, the pregelatinization process improved the compressibility and flowability of Plectranthus edulis starch and the modified starch product has better flowability and compressibility than native Plectranthus edulis starch and Starch 1500. Hence, pregelatinized Plectranthus edulis starch can be used as an alternative direct compression excipient in tablet formulations.
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direct compression, dilution potential, filler-binder, lubricant sensitivity Plectranthus edulis starch, pregelatinization