The IR spectra of pure showed peaks at which are consistent with the presence of the functional groups of lisinopril (Fig.no.12) Furthermore, the calibration curve of lisinopril obeyed Beer’s law in the range of 10-60 g/ml (Fig.no.11)
An IR spectrum of the drug-polymer (methylcellulose) mixture was taken to study and check the drug- polymer interaction. The spectrum revealed that not much interaction between the drug and polymer (Fig.no.13).
In TLC studies, the prepared lisinopril microspheres (M4, M7) showed (Table.no.9) the same Rf (0.5512, 0.5769) value as pure compound (0.5897) and no additional spots were detected. TLC studies (Fig.no15) thus indicated no interaction between lisinopril and polymer (methylcellulose) in the floating microspheres prepared. This observation also indicated that lisinopril was not decomposing during the preparation of floating microspheres.
Differential Scanning Colorimetry:
The thermal behavior of floating microspheres of lisinopril was studying using DSC are shown in (Fig no.16). The DSC thermogram of pure drug lisinopril exhibited an exothermic peak at corresponding to its melting point. For formulation (M7) this peaks are at respectively. The characteristic exothermic peak is slightly shifted to lower temperature, indicating that there is no interaction between drug and carrier.
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Percentage yield:
Percentage yield of different batches of the prepared floating microspheres were determined by weighing the floating microspheres after drying. All batches of methylcellulose floating microspheres showed a percentage yield of greater than 75%, the percentage yields of all the prepared formulations (M1-M9) were in the range of 76.8 to 92.16% (Table.no.11). Percentage yield is found to be higher with formulation M7 (92.16%).
Scanning Electron Microscopy:
The surface morphology of the prepared floating microsphere (M7) was shown to be spherical by the SEM photography (Fig.no.19).
Particle size analysis:
The particle size analysis was carried out using an optical microscope. The arithmetic mean particle size of the methylcellulose floating microspheres significantly increased with increasing polymer concentration were shown in (Table.no.18).The particle size distribution of the methylcellulose floating microspheres ranged between 163.125 to 252.375µm.
Micromeritic properties of the floating microspheres 61
The various micromeritic properties of the prepared floating microspheres were studied.
Acceptable range of angle of repose is between 20ο-40ο and angle of repose for methylcellulose floating microspheres (M1-M9) was between 24.44 to 35.53ο (Table no. ), thus indicating good flow property for methylcellulose floating microspheres.
Acceptable range of Hausner’s ratio is up to 1.25 and Hausner’s ratio for methylcellulose floating microspheres(M1-M9) was between 1.085 to 1.181(Table.no.21) ,all the prepared floating microspheres had a value less than 1.25 thereby exhibiting good flow properties.
Acceptable range of Carr,s index (%)is up to 5-21%, and carr’s index for methylcellulose floating microspheres(M1-M9) was between 7.910 to 15.379 % (Table.no.21) all the formulations showed an Carr,s index (%) less than 16% and hence had a flow properties.
Percentage drug content of the floating microspheres
The percentage drug content of different batches of floating microspheres was found in the range of 55.33 to 88%.All batches of the methylcellulose floating microspheres formulation shown percentage drug content more than 55% (Table no.23) and it is found that percentage drug content increases with an increase in the polymer concentration (except M2,M6). Formulation M5 has shown maximum percentage drug content (88.0%).
Buoyancy percentage: (Floating ability)
The buoyancy test was carried out to investigate the buoyancy percentage (floating ability) of the prepared methylcellulose floating microspheres. The buoyancy percentage of the different batches of floating microspheres was found in the range of 48.0 to 85.0% at the end of 12 hrs (Table.no.25). All the formulated floating microspheres of lisinopril showed buoyancy (floating ability) more than 48%. Amongst the batches of prepared methylcellulose floating microspheres, batch M5 showed highest buoyancy (85%). Floating ability of different formulations was found to be differed according to the increase polymer concentration and it is found that percentage of buoyancy increases with an increase in the amount of polymer.
In-vitro release studies
Lisinopril release from the all formulated floating microspheres were studied in SGF (0.1N HCl) for 12 hrs.The floating microspheres showed sustained release of the lisinopril (drug) in acidic environment and the drug release was found to be approximately linear (fig no. ). The drug release from methylcellulose floating microspheres was found to be 82.35, 78.75, 74.25, 71.55, 66.15, 83.70, 90.45, 94.5 and 97.65% at the end of 12 h for M1,M2,M3,M4,M5,M6,M7,M8 and M9 respectively (Table.no.27). The sustained release pattern was observed for the prepared floating microspheres (M1-M9) clearly exhibiting an increase in the polymer concentration results decrease in-vitro drug release of lisinopril. Amongst the batches of prepared methylcellulose floating microspheres, batch M5 showed higher drug entrapment efficiency 88.0% and the minimal in-vitro drug release 66.15% at the end of the 12 hrs with compared to the other prepared methylcellulose floating microspheres.
Drug release kinetics
The results for the mathematic modeling of the in-vitro drug release data for the methylcellulose floating microspheres have been complied and the R2 values shown in the table no.
The in-vitro drug release profile for the formulations M1-M9 were subjected to various drug release kinetic studies and are depicted in the following figures. (Fig.no.30-38)
The release profile for the formulations M1-M9 exhibiting a maximum R2 values (0.9613, 0.9421, 0.9386, 0.9446, 0.9382, 0.9546, 0.9520, 0.9599 and 0.9660) was found to obey that particular kinetics. From the results it is apparent that the regression coefficient value closer to unity as in the case of the Zero orders plots. The Zero order plots of different formulation were found to be fairly linear, as indicated by their high regression values. Thus, it seems that drug release from the floating microspheres followed Zero order kinetics. The data indicates a lesser amount of linearity when plotted by the First order equation. Hence it can be concluded that the major mechanism of drug release follows Zero order kinetics.
Further, the conversion of the data from the dissolution studies suggested possibility of understanding the mechanism of drug release by configuring the data into various mathematical modeling such as Higuchi’s and Korsemeyer’s -peppas plots. The mass transfer with respect to square root of time has been plotted, revealed a linear graph with regression value close to one stating that the release from the matrix was through diffusion. Data based on the Higuchi model usually provide a evidence to the diffusion mechanism of drug release from matrix systems such as the methylcellulose floating microspheres developed in this work. R2 values based on the Higuchi’s model ranged from 0.8882, 0.8578, 0.8507, 0.8603, 0.8542, 0.8773, 0.8708, 0.8858 and 0.8978. (Table.no.29). As these values were close to 1.0, the drug release mechanism of the developed floating microspheres can be said to be Higuchian and, therefore, matrix diffusion-controlled.
CHITOSAN FLOATING MICROSPHERES
IR Spectra of chitosan floating microspheres
An IR spectrum of the drug-polymer (chitosan) mixture was taken to study and check the drug- polymer interaction. The spectrum revealed that not much interaction between the drug and polymer (Fig.no.14).
Thin Layer Chromatography:
In TLC studies, the prepared lisinopril microspheres (C4, C7) showed the same Rf (0.5384, 0.5000) value as pure compound (0.5897) and no additional spots were detected(Fig.no.15). TLC studies thus indicated no interaction between lisinopril and polymer (chitosan) in the floating microspheres prepared. This observation also indicated that lisinopril was not decomposing during the preparation of floating microspheres.
Differential Scanning Colorimetry:
The thermal behavior of floating microspheres of lisinopril was studying using DSC are shown in Fig.no.17. The DSC thermogram of pure drug lisinopril exhibited an exothermic peak at corresponding to its melting point. For formulation (C7) this peaks are at respectively. The characteristic exothermic peak is slightly shifted to lower temperature, indicating that there is no interaction between drug and carrier.
Percentage yield:
Percentage yield of different batches of the prepared floating microspheres were determined by weighing the floating microspheres after drying. All batches of methylcellulose floating microspheres showed a percentage yield of greater than 75%, The percentage yields of all the prepared formulations (C1-C9) were in the range of 78.0 -93.66% (Table.no.12). Percentage yield is found to be higher with formulation C7 (93.66%).
Scanning Electron Microscopy:
The surface morphology of the prepared floating microsphere (C7) was shown to be spherical by the SEM photography (Fig.no.20).
Particle size analysis:
The particle size analysis was carried out using an optical microscope. The arithmetic mean particle size of floating microspheres significantly increased with increasing polymer concentration were shown in Table. No. 19. The particle size distribution of the chitosan floating microspheres ranged between 32.50 to 55.80µm.
Micromeritic properties of the floating microspheres 61
The various micromeritic properties of the prepared floating microspheres were studied.
Acceptable range of angle of repose is between 20ο-40ο and angle of repose for chitosan floating microspheres (C1-C9) was between 19.02 to 23.49ο (Table.no.22), thus indicating good flow property for chitosan floating microspheres.
Acceptable range of Hausner’s ratio is up to 1.25 and Hausner’s ratio for chitosan floating microspheres(C1-C9) was between 1.100 to 1.230 (Table.no.22) ,all the prepared floating microspheres had a value less than 1.25 thereby exhibiting good flow properties.
Acceptable range of Carr,s index (%)is up to 5-21%, and carr’s index for chitosan floating microspheres(C1-C9) was between 9.090 to 18.746% (Table.no.22) all the formulations showed an Carr,s index (%) less than 18% and hence had a flow properties.
Percentage drug content of the floating microspheres
The percentage drug content of different batches of floating microspheres was found in the range of 50.66 to 88.0%.All batches of the chitosan floating microspheres formulation shown percentage drug content more than 50% (Table.no.24) and it is found that percentage drug content increases with an increase in the polymer concentration. Formulation C5 shown maximum percentage drug content (88.0%).
Buoyancy percentage: (Floating ability)
The buoyancy test was carried out to investigate the buoyancy percentage (floating ability) of the prepared chitosan floating microspheres. The buoyancy percentage of the different batches of floating microspheres was found in the range of 46.0 to 82.0% at the end of 12 hrs (Table.no.26). All the formulated floating microspheres of lisinopril showed buoyancy (floating ability) more than 46%. Amongst the batches of prepared chitosan floating microspheres, batch C5 showed highest buoyancy (85%). Floating ability of different formulations was found to be differed according to the increase polymer concentration and it is found that percentage of buoyancy increases with an increase in the amount of polymer.
In-vitro release studies
Lisinopril releases from the all formulated floating microspheres were studied in SGF (0.1N HCl) for 12 hrs.The floating microspheres showed sustained release of the lisinopril (drug) in acidic environment and the drug release was found to be approximately linear (Fig.no.29). The drug release from chitosan floating microspheres was found to be 66.6, 61.65, 58.95, 57.15, 52.2, 69.3, 71.55, 74.7 and 78.75% at the end of 12 h for C1,C2,C3,C4,C5,C6,C7,C8 and C9 respectively (Table.no.28). The sustained release pattern was observed for the prepared floating microspheres (C1-C9) clearly exhibiting an increase in the polymer concentration results decrease in-vitro drug release of lisinopril. Amongst the batches of prepared chitosan floating microspheres, batch C5 showed higher drug entrapment efficiency 88.0% and the minimal in-vitro drug release 52.2% at the end of the 12 hrs with compared to the other prepared chitosan floating microspheres.
Drug release kinetics
The results for the mathematic modeling of the in-vitro drug release data for the methylcellulose floating microspheres have been complied and the R2 values shown in the table no.
The in-vitro drug release profile for the formulations C1-C9 were subjected to various drug release kinetic studies and are depicted in the following figures. (Fig.no.39-47)
The release profile for the formulations C1-C9 exhibiting a maximum R2 values (0.9834, 0.9646, 0.9556, 0.9244, 0.9305, 0.9656, 0.9655, 0.9646, and 0.9759) were found to obey that particular kinetics. From the results it is apparent that the regression coefficient value closer to unity as in the case of the Zero orders plots. The Zero order plots of different formulation were found to be fairly linear, as indicated by their high regression values .Thus, it seems that drug release from the floating microspheres followed Zero order kinetics. The data indicates a lesser amount of linearity when plotted by the First order equation. Hence it can be concluded that the major mechanism of drug release follows Zero order kinetics.
Further, the conversion of the data from the dissolution studies suggested possibility of understanding the mechanism of drug release by configuring the data into various mathematical modeling such as Higuchi’s and Korsemeyer’s -peppas plots. The mass transfer with respect to square root of time has been plotted, revealed a linear graph with regression value close to one stating that the release from the matrix was through diffusion. Data based on the Higuchi model usually provide a evidence to the diffusion mechanism of drug release from matrix systems such as the chitosan floating microspheres developed in this work. R2 values based on the Higuchi’s model ranged from 0.9238, 0.8905, 0.8751, 0.8295, 0.8392, 0.8955, 0.8993, 0.8986 and 0.9236. (Table.no.30). As these values were close to 1.0, the drug release mechanism of the developed floating microspheres can be said to be Higuchian and, therefore, matrix diffusion-controlled.
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