Bioavailability parameters are reported in Table 6. These results
demonstrate that the selected formulation behaves as a sustained
release formulation. Comparison of the observed AUC value with
the AUC value of the commercial sustained release formulation
of theophylline (Henrist et al., 1999) indicates a trend of improved
bioavailability. The observed values of t1/2,z were higher than the
reported theophylline elimination half-life of 6–10 h (Jonkman
et al., 1989), indicating a flip-flop phenomenon. The rate of absorption
was therefore manifested in the terminal slope of the concentration–
time curve. In vivo behavior of the tested formulation was
similar to the previously evaluated experimental sustained release
cluster matrix tablets containing hydrophobic wax and hydrophilic
polymer granules (Hayashi et al., 2007).