Results and discussion
Incorporating the highly porous powder in the matrix tablets results in densities that are lower than the density of the
release medium (compared with 1.00 g/cm for the release the medium). Approximately 12% w/w of low-density copolymer powder
(based on the mass of the tablet) was sufficient to achieve proper in vitro floating behavior for at least 8 h. In contrast to most conventional floating systems (including gas-generating systems),
these tablets floated immediately upon contact with the release medium and thus showed no lag times in floating (time = 0).
Extended floating times were achieved as a result of the air entrapped within the low-density powder particles, which is only
slowly removed from the system upon contact with the release medium. As expected, tablets without poly(styrene–divinyl benzene)
copolymer powder (e.g., consisting of 40 mg of polymer and 40 mg of famotidine) sank to the bottom of the vessel showing no
floating behavior.Adding 15% w/w (based on the mass of the tablet) of low-density powder reduced the lag times to 0 s.
drug release. To evaluate the hydrophilic matrixing polymers used to prepare floating matrix tablets; seven polymers (sodium alginate,
Xanthan 150, Klucel HXF, chitosan, psyllium, HPMC K15 M, and HPMC K100 M) were selected and dosage forms were prepared and
evaluated for individual drug-release profiles. Approximately 12.6 % of low-density powder was added to these formulations
initially. Results showed that the type of polymer influenced the drug-release pattern (see Figure 1).
Figure 1: Effect of various matrix-forming polymers on drug release using USP paddle method.
A significantly lower rate and extent of drug release was observed from the batches B2, B3, and B6 compared with batches B1
and B7. Formulations made with chitosan (batch B4) and psyllium (batch B5) eroded at the end of 6 h, releasing 98.96 % and
99.98 % of drug, respectively. These polymers were therefore unsuitable for the desired floating matrix tablets of famotidine.
The integrity of tablets made with chitosan was much better than that of tablets prepared with psyllium. The initial burst
effects for the formulations B2, B3, and B6 were much lower than the required theoretical value, while those for formulations
B1 and B7 (containing sodium alginate and HPMC K15 M) were near to the required theoretical profile value (which was calculated
using the equations of immediate-release dose and maintenance dose). The floating lag time for most of the batches was within
5 s. Thus the low density powder poly(styrene-divinyl benzene) copolymer (PSDVB) showed its role in the buoyancy of the formulations.