Compressed donut-shaped tablets with zero-order release kinetics

Simple uncoated compressed tablets with a central hole (donut-shape) are proposed to provide a constant drug release over a long period of time (> 20 hrs). The effect of hole size and drug solubility on the release kinetics is investigated.

The donut-shaped polyethylene oxide (PEO, Mw = 4 x 10(6)) tablets (600 mg and 12 mm diameter) are bored with a drill bit (3/32", 7/64", 1/8", and 5/32").

The release of theophylline from the donut-shaped tablets is zero order (80-90% release) before rapidly decreasing. As the hole size is increased from 7/64" to 5/32", the release rate increases and the release time is shortened. However, the release of theophylline from the donut-shaped tablet with a hole size of 3/32" follows the same anomalous release profile from a tablet without a hole. As drug solubility increases, the duration of linear drug release is shortened to 65-70% release followed by a severe tailing at the later stage of the release.

Donut-shaped PEO tablets with a hole provide zero-order release kinetics because the effect of the releasing surface area on the release kinetics is reduced.