COMPRESSED DONUT-SHAPED TABLETS WITH ZERO-ORDER RELEASE KINETICS

Purpose. 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. Methods. The donut-shaped polyethylene oxide (PEO, Mw=4x10(6)) tablets (600 mg and 12 mm diameter) are bored with a drill bit (3/32 '', 7/64 '', 1/8 '' and 5/32 ''. Results. 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. Conclusions. Donut-shaped PEG tablets with a hole provide zero-order release kinetics because the effect of the releasing surface area on the release kinetics is reduced.