In vitro--in vivo evaluation of tableted caseinchitosan microspheres containing diltiazem hydrochloride

Casein-chitosan microspheres containing diltiazem hydrochloride (DTZ.HCL) were prepared using aqueous coacervation technique. The formed microspheres were not suitable for tableting by direct compression due to their poor binding properties. The effect of hydroxypropylmethylcellulose (HPMC), ethylcellulose (EC), carbopol 940 and egg albumin as dry binders at different concentrations on the properties of the tablets was studied. Each blend of microspheres with dry binder and 2% w/w magnesium stearate as glidant was hand-filled into the die cavity of a single punch tablet machine to ensure constant amount of drug (90 mg) in each tablet. The compression force was adjusted to produce tablets with hardness value about 7.73 +/- 0.79 Kp. The prepared tablets showed good appearance and low friability. The tested binders HPMC (10 and 30% w/w) and EC (20 and 30% w/w) gave fast tablet disintegration with high initial drug release (burst effect) while, carbopol 940 (5 and 10% w/w) and egg albumin (30% w/w) gave non-disintegrating tablets with low initial drug release. Tableted microspheres prepared with 30% egg albumin showed drug release profile similar to one of the commercial tablets (Dilzem retard, 90 mg) and was chosen for in-vivo study. Tableted microspheres and commercial tablets were administered orally in different occasions to six beagle dogs and diltiazem was assayed in dog plasma. The pharmacokinetic parameters including maximum drug concentration (Cmax) and time to reach that maximum (Tmax) were 106.24 +/- 17.96 ng.ml-1 and 5.8 +/- 2.04 hours, respectively, for the commercial sustained release DTZ tablets while, those were 107.9 +/- 12.89 ng.ml-1 and 3.6 +/- 1.36 hours, respectively for tableted microspheres. The elimination half-lives were nearly the same for the commercial and the formulated tablets (8.22 +/- 4.19 and 7.95 +/- 4.28 hours, respectively). No statistical differences (P > 0.05) were found between the two treatments for area under the plasma concentration curve (AUC0 infinity), mean residence time (MRT) and rate of drug absorption (Cmax/AUC0 infinity) indicating comparable extent and rate of drug absorption for both formulations. It was concluded that the formulated tableted microspheres provide an acceptable delivery for DTZ over an extended period of time.