Formulation and evaluation of time-controlled triple-concentric mefenamic acid tablets for rheumatoid arthritis

A triple-concentric time-controlled release mefenamic acid (MA) tablet was developed using Carbopol and Ethocel polymers. The burst dose was programed to release immediately after an ingestion of tablet to be followed by a lag period of 2-4 h, and thereafter an 8 h controlled release of MA from core tablet. Core tablets were prepared using Carbopols 971P, 974P, 71G or 907 at various concentrations. The core tablet provided a controlled release of MA and the release rate decreased with increasing polymer concentration. Highly cross-linked Carbopol 974P released MA at a faster rate compared to release from Carbopol 971P with medium degree of cross-linking. Carbopols 71G and 971P exhibited essentially similar release rates. Carbopol 907, a linear polymer, showed fastest release of MA. The extent of uptake of dissolution medium by core tablets was inversely related to the rate of release of MA from the tablets. Compression coating of core tablet with Ethocel provided the lag period to delay release of MA from core tablet. Increase in lateral coating thickness decreased MA release and increased lag period. Compression forces applied during compression coating with Ethocel for lag period, and immediate-release MA coating for burst release did not affect the integrity of core tablet.