Potential application of silicified microcrystalline cellulose in direct-fill formulations for automatic capsule-filling machines

Silicified microcrystalline cellulose (SMCC) has physico-mechanical properties that may be of advantage in hard gelatin capsule formulations. The present research was designed to evaluate and compare SMCC's performance to that of other excipients commonly used in hard gelatin capsule direct-fill formulations. All capsules were filled using a fully instrumented Zanasi LZ-64 automatic capsule-filling machine. Four grades of SMCC [SMCC 50, SMCC 90, SMCC HD90, and an experimental-grade (SMCC X)] were investigated. Anhydrous lactose (direct tableting grade), pregelatinized starch (PGS) (Starch 1500), and microcrystalline cellulose (MCC) (Emcocel 90M) were chosen as the control fillers. The following properties were measured: capsule fill weight, relative standard deviation of capsule fill weight, plug ejection force, plug maximum breaking force (MBF), and the dissolution of two marker compounds (acetaminophen and piroxicam). The MBF of capsule plugs increased with increases in compression force from 50N to 100N for all excipients. Starch 1500 and anhydrous lactose plugs exhibited the lowest MBF values. PGS, anhydrous lactose, SMCC HD90, and SMCC X consistently exhibited the lowest ejection forces under the same experimental conditions, this difference being most apparent at higher compression forces. Different patterns were observed in the way compression force affected the fill weight of the materials studied. Overall, there was no clear pattern to the way the relative standard deviation (RSD) of capsule fill weight varied with encapsulation conditions. Sodium stearyl fumarate (SSF) appeared to be somewhat more efficient at reducing the ejection force than magnesium stearate at the same level, this difference being especially apparent at the 14-mm piston height. Formulations containing either 5% piroxicam, 30% acetaminophen, or 50% acetaminophen exhibited faster drug dissolution when MCC or SMCC was the filler than when anhydrous lactose or PGS was the filler. The presence of colloidal silicon dioxide in SMCC did not appear to influence the dissolution of these drugs. The data suggest that SMCC could be a suitable direct-fill excipient for hard shell capsule formulations.