Preparation of press-coated tablets. The press-coated tablets were prepared according to the method described by Fukui (8). All powder mixtures were passed through
a sieve no. 44, and 150 mg of the powder mixture was used for the upper and lower shells. Press coating was performed using
a rotary tablet machine. Half (150 mg) of the powder was filled into the die to make a powder bed, and the core tablet was
placed manually in the center. The remaining half of the coating material was used to fill the die, and the contents were
compressed under a sufficient compression force (total weight = 375 mg) using a concave punch 10 mm in diameter to keep the
hardness of the coated tablet at 10 ± 0.34 kg/cm2 .
Formulations for the outer shell of press-coated tablets. The formulation of the outer shell for the press-coated tablet using core tablet containing 4% Ac-Di-Sol and Starlac or Avicel
PH 101 as filler was respectively prepared according to the following formulas:
- rupturable polymer (EC) combined with erodible polymer (HPC EXF): weight ratios of HPC EXF to EC N 22 F were 0:100%, 12.5:87.5%,
25:75%, 50:50%, 75:25%, 87.5:12.5%, and 100:0% w/w;
- gellable polymer (HPC HF) combined with erodible polymer (HPC EXF): weight ratios of HPC HF to HPC EXF were 0:100%, 12.5:87.5%,
25:75%, 50:50%, 75:25%, 87.5:12.5%, and 100:0% w/w.
In vitro dissolution study. To verify how the composition of the core and the barriers interferes with the drug-release profile from the cores, the in vitro release behavior of the uncoated cores and press-coated tablets were tested. The test was carried out in a USP dissolution
paddle assembly (model DT 60, Veego, India) at 37 ± 0.5 °C using 0.1 N HCl (first fluid; simulated gastric fluid) for the
first 2 h. The tablets then were transfered to 6.8 pH phosphate buffer (second fluid; simulated intestinal fluid) solution.
Aliquots of dissolution fluid were removed at specified time intervals and assayed for the amount of salbutamol sulfate released
by a spectrophotometer (UV 1700, Shimadzu, Japan) at wavelengths of 224.5 and 225 nm for 0.1 N HCl and 6.8 pH phosphate buffer,
respectively. The in vitro release patterns of the cores were studied visually by taking images of the tablets in a Petri plate containing dissolution
medium. All dissolution studies were performed in triplicate (n = 3) to obtained mean and standard deviation.
Erosion study of press-coated tablets. The erosion study of press-coated tablets was designed to determine whether the prevailing release mechanism of salbutamol
sulfate from the coated devices depends on the types of core composition. The percentage of erosion from the press-coated
tablets was determined in the dissolution medium just before lag time. At predetermined time points (before lag time), the
tablets were removed from the dissolution medium, carefully blotted with tissue paper to remove surface water, and weighed.
The percentage of erosion was calculated as follows (9):
in which Wt is the weight of wet tablet at time t and W0 is the weight of the dry coated tablet.