Continuous direct tablet compression: effects of impeller rotation rate, total feed rate and drug content on the tablet properties and drug release.

CONTEXT: Continuous processing is becoming popular in the pharmaceutical industry for its cost and quality advantages.

OBJECTIVE: This study evaluated the mechanical properties, uniformity of dosage units and drug release from the tablets prepared by continuous direct compression process.

MATERIALS AND METHODS: The tablet formulations consisted of acetaminophen (3-30% (w/w)) pre-blended with 0.25% (w/w) colloidal silicon dioxide, microcrystalline cellulose (69-96% (w/w)) and magnesium stearate (1% (w/w)). The continuous tableting line consisted of three loss-in-weight feeders and a convective continuous mixer and a rotary tablet press. The process continued for 8 min and steady state was reached within 5 min. The effects of acetaminophen content, impeller rotation rate (39-254 rpm) and total feed rate (15 and 20 kg/h) on tablet properties were examined.

RESULTS AND DISCUSSION: All the tablets complied with the friability requirements of European Pharmacopoeia and rapidly released acetaminophen. However, the relative standard deviation of acetaminophen content (10% (w/w)) increased with an increase in impeller rotation rate at a constant total feed rate (20 kg/h). A compression force of 12 kN tended to result in greater tablet hardness and subsequently a slower initial acetaminophen release from tablets when compared with those made with the compression force of about 8 kN.

CONCLUSIONS: In conclusion, tablets could be successfully prepared by a continuous direct compression process and process conditions affected to some extent tablet properties.