Stability studies
The developed MCNNs in the present study were subjected to the stability testing and the intactness of the drug during preparation of system and effects of exposure to different storage conditions were determined.
The developed drug delivery systems were evaluated for the following parameters.
1. Percent residual drug content 2. Vesicle size
The stability of natamycin loaded mucoadhesive cationic niosomes in different physical states and storage conditions was examined (1). Physical stability of MCNNs were performed to determine the loss of drug from niosomes, change in vesicle size and zeta potential during storage. Both niosomal formulations i.e. freshly prepared niosomes (FPNs) and reconstituted niosomes (RCNs), were placed in screw capped small glass bottles of 20 mL capacity and stored at 4±1°C, ambient room temperature (27±1°C) and high temperature (40±1°C) in stability study chambers, for a period of 3 months. For a definite time, intervals (at day 0, 15, 30, 45, 60, 75 and 90) samples were taken from each drug delivery system. The samples were subjected to % residual drug content and vesicle size observations (2).
Estimation of effect of storage temperature on residual drug content of carrier systems The drug content of niosomal system was also determined at the stability storage conditions. After storage, samples from the stored system were collected at 15th, 30th, 45th, 60th, 75th and 90th day. For the residual drug content analysis, the drug leached from drug delivery systems were separated by centrifugation at 20,000 rpm at 4°C for 30 min and the collected samples were diluted and aliquots prepared with phosphate buffered saline (pH 7.4) (3). These aliquots were analysed by HPLC method as reported in chapter previous chapter. The observations were reported in figure S4 (a) and (b).
Fig. S4 (a). Effect of different storage temperatures on residual drug content of FPNs (freshly
prepared niosomes)
Fig. S4 (b). Effect of different storage temperatures on residual drug content of RCNs (Reconstituted niosomes)
0 10 20 30 40 50 60 70 80 90
0 15 30 45 60 75 90
% Residual drug content
Time (days)
% Residual drug content of FPNs at different storage temperatures FPNs at 4±1°C FPNs at 27±1°C FPNs at 40±1°C
0 10 20 30 40 50 60 70 80 90
0 15 30 45 60 75 90
% Residual drug content
Time (days)
% Residual drug content of RCNs at different storage temperatures RCNs at 4±1°C RCNs at 27±1°C RCNs at 40±1°C
Estimation of effect of storage temperature on vesicle size
Change in vesicle size of the carriers (FPNs and RCNs) stored at 4±1C, 27±1C and 40±1C was monitored using a NanoPlus- 3 (Version 5. 01, Micromeritics Instrument Corporation, Particulate Systems, Norcross, GA, USA) by Photon Correlation Spectroscopy (PCS), 0th, 15th, 30th, 45th, 60th, 75th and 90th day Testing of stability of the niosomes was performed in triplicate. The results obtained from stability studies are showing in figure (S5 a and b).
Fig. S5 (a). Effect of temperature on vesicles sizes of FPNs
at different storage temperatures
600 700 800 900 1000 1100 1200 1300 1400 1500 1600
0 15 30 45 60 75 90
vesicle size (nm)
Time (days)
Vesicle size of FPNs at different storage temperature
FPNs at 4±1°C FPNs at 27±1°C FPNs at 40±1°C
Fig. S5 (b). Effect of temperature on vesicles sizes of RCNs at different storage temperatures
Results and discussion
Stability studies of the niosomes were performed in order to evaluate the ability of the developed dosage form to withstand environmental stress i.e. temperature, pH, humidity etc. as well as to retain the stability of the entrapped drug. In other words, the stability study was performed in order to investigate any type of degradation in drug delivery system during the storage. The storage stability at different temperatures was determined (4). A stable formulation must exhibit a less significant change in the vesicle size and drug content. The present study was desired to estimate the stability of freshly prepared and reconstructed optimized niosomes.
Physical stability study of FPNs and RCNs were conducted at lower temperature (4 ±1°C), ambient room temperature (27±1°C) and high temperature (40 ±1°C) for a period of 3 months (5). Drug leakage (residual drug content), vesicle size and zeta potential from the niosomal formulations were measured at definite time intervals
Effect of temperature on residual drug content
When the storage period increased, the leakage of drug from niosomes also increased.
Both freshly prepared and reconstituted mucoadhesive cationic niosomes were subjected to stability studies after storage at various temperatures (6, 7). It is observed that the average percent residual drug content of the niosomes is found to decrease on storage, which may be due
0 200 400 600 800 1000 1200 1400 1600
0 15 30 45 60 75 90
Vesicle size (nm)
Time (days)
Vesicle sizes of RCNs at different storage temperatures
RCNs at 4±1°C RCNs at 27±1°C RCNs at 40±1°C
to leakage of drug from the drug delivery systems. This effect was encountered lower in the case of dosage forms stored at 4°C as compare to 27C and 40 C. After day zero, in case of storage at 4°C, initial percent residual drug content of FPNs and RCNS were found to be 81.23 ±2.09 and 80.68±3.14 respectively. Percent residual drug content is decreased up to 70.432.47 (RCNs) and 72.06 3.23 (FPNs) after 90 days when FPNs and RCNs were placed at this lower temperature. Storage at 4°C, niosomes were shown less change in the drug content as compared to other higher temperatures. But when higher temperatures (27C and 40C) were taken for storage, the percent residual drug content for both types of niosomes were decreased at higher rate. But these deductions were more significantly seen when dosage forms were subjected to 40C [figure S4 (a and b)]. On comparing the FPSs and RCNs, FPNs show less leakage of natamycin. Higher temperature could enhance the rate of drug leakage due to disruption of structure. The niosomal suspension may aggregate/fuse during the storage and the entrapped drug was leached from the vesicles. At higher temperature the surfactant and lipid might be melted which was responsible for higher drug loss from the vesicles. At lower temperature the vesicles were rigid and decrease the leakage of drug from the vesicles. These results demonstrated that the niosomes were stable at low temperature as compared to room and higher temperature. Therefore, the niosomal formulations can be stored at either refrigeration or lower temperature (8, 9).
Effect of temperature on vesicle size
The average vesicle size of the niosomes was found to increase on storage, which may be due to aggregation of vesicles at prolong storage at higher temperature. This effect was found lower in the case of carrier system stored at 4°C. When both drug delivery systems (FPNs and RCNs) were subjected to stability studies at 4oC, initial vesicle size of FCNs and RCNs was recorded as 1031.33 ± 10.78 nm and 1033.89 ± 12.08 nm, respectively. Size of these vesicles was found to be increased up to 1069.6±9.23 nm (FPNs) and 1073.9±11.44 nm (RCNs) after 90 days. These changes were less significant as compared to other storage stability testing temperature. The stability studies performed at ambient room temperature, after 90 days the vesicle size of FPNs and RCNs were found to be 1186.11 ± 8.41 nm and 1189.65 ± 10.3 nm, respectively. When FPNS and RCNS were placed at higher temperature (40oC) for stability testing. The size of vesicles were obtained as 1293.89±9.13 nm (FPNs) and 1301.29±10.44 nm (RCNs) at 90th day [figure S5 (a) and (b)].
The results from above three different storage temperature, 4oC is suggesting as the storage temperature of niosomes because at this temperature, slow aggregation was observed.
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