The MDT value of LVS from pure LVS, the physical mixture, and complexes prepared by the coevaporation and the kneading methods
were calculated (n = 3) using the equation:
in which i cr, n is the number of dissolution times, tmid is the time at the midpoint between times ti and ti–1, and ΔM is the amount of LVS dissolved (μg)
between times ti and t i–1. The obtained values of MDT for pure LVS, the physical mixture, and complexes prepared by the coevaporation and the kneading
method are presented in Table IV. MDT reflects the time for the drug to dissolve and is the first statistical moment for the
cumulative dissolution process that provides an accurate drug-release rate (17). It is an accurate expression for drug-release
rate. A higher MDT value indicates greater drug-retarding ability (18). The MDTs of LVS are 64.92 min in DM-A and 66.13 min
in DM-B. These values decreased a greater extent after the preparation of a complex of LVS with HPβ-CD (e.g., 22.00 min in DM-A and 30.56 min in DM-B for the kneading method and 33.79 min in DM-A and 41.08 min in DM-B for the coevaporation
method). The physical mixture also shows sufficiently lower MDT value compared with pure LVS in both dissolution media. The
kneading method, which exhibited the best dissolution profile, was used for the formulation studies.
Figure 7: In vitro dissolution profiles of pure lovastatin and its physical mixture and complexes in dissolution media-A (0.1
N HCl) (tests performed in triplicate). CPK is the kneading method, CPC is the co-evaporation method, PM is the physical mixure,
and LVS is lovastatin.
A value of 100% for the similarity factor (f2) suggests that the test and reference profiles are identical. Values between 50 and 100 indicate that the dissolution profiles
are similar, whereas smaller values imply an increase in dissimilarity between release profiles (14). Calculated f2 values are presented in Table V. From this table, it is evident that the release profile of LVS prepared by the kneading
method is very different from pure LVS in both dissolution media (f2 values 10.55 in DM-A and 11.64 in DM-B). Even release profiles of LVS prepared by the coevaporation method and the physical
mixture also are significantly different from pure LVS in both dissolution media.
Table III: The % drug dissolved within 30 minutes (DP30 min) and the time to dissolve 50% of the drug (t50%) from pure lovastatin
(LVS), the physical mixture (PM), and complexes made with the coevaporation (CPC) and the kneading methods (CPK) in DM-A*