Selection of the best batch.
The comparative results of various formulation batches were compared with theoretical dissolution profile using the similarity
factor f2 test and the floating lag time of each batch. Results of similarity tests depicted that among all the batches, batch HC3,
which contained 40 mg HPMC K15M, 20 mg chitosan, and 30 mg PSDVB copolymer, showed an f2 value >> 50, indicating good fit with theoretical dissolution profile. Other criteria for the selection of best batch were
that the formulation should release drug in predictable and controlled manner and have a floating lag time less than 15 s.
Further to evaluate complete similarity two check points (t
30
and t
80
) were considered in the dissolution profiles of all the batches. Results in Table II indicate that the t
30
of 1.9 h and t
80
of 6.3 h of batch HC3 show that the drug release is in a sustained manner for that formulation.
Swelling index.
The swelling index of tablets was determined in 0.1 N HCl (pH 1.2) at room temperature. The swollen weight of the tablets
was determined at predefined time intervals. The swelling index was calculated using the following equation:
Swelling index = (W
t
– W
0
) ÷ W
0
in which W
0
is the initial weight of tablet, and W
t
is the weight of the tablet at time t.
Tablets composed of polymeric matrices build a gel layer around the tablet core when they come in contact with water. This
gel layer governs the drug release. Kinetics of swelling is important because the gel barrier is formed with water penetration.
Swelling is also vital factor to ensure floating. To obtain floating, the balance between swelling and water acceptance must
be restored (17, 18). The swelling index of the best batch after 8 h was 1.686, which may be attributed to the high viscosity
and high water-retention property of HPMC K15 M.
Figure 4: Comparison of dissolution profile before and after stability studies of batch HC3.
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Accelerated stability study of the optimized batch.
Gastroretentive tablets of famotidine formulated in the present study were subjected to accelerated stability studies in
aluminum–aluminum pouch pack also known as an aluminum blister (using Alu-Alu blister packing machine, Pam Pac Machines, Mumbai,
India). As the dosage form is formulated for site-specific drug delivery to the stomach, no change should occur in its floating
lag time and drug dissolution profile. Dose dumping and failure of buoyancy are probable effects anticipated during the stability
study of such dosage forms. The tablets of batch HC3 were packed in an aluminum pouch and charged for accelerated stability
studies at 40 °C and 75% relateive humidity for 3 months in a humidity jar. Floating lag time test and a drug dissolution
profile of exposed samples were carried out. Results of the accelerated stability studies are shown in Figure 4.
The similarity factor f
2
was calculated for comparison of the dissolution profile before and after stability studies. The f
2
value was >50 (approximately 76.42), which indicates a good similarity between both dissolution profiles. Similarly, no significant
difference was observed in the floating lag time after stability studies. Therefore, the results of those stability studies
revealed that the developed formulation had good stability.
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