Seminar Addresses Developments and Challenges in Hot Melt Extrusion

Development in hot melt extrusion (HME) using twin-screw extruders to make solid-dosage drug forms has increased significantly in the past decade, although it is still in its infancy, said Charlie Martin, president of the US operations of Leistritz at the recent Pharmaceutical Extrusion Seminar organized by the company. An interesting aspect of HME is the variety of physical forms that can be given to the melt after mixing.

At Leistritz’s processing lab, for example, seminar attendees observed demonstration lines producing cast film, tubing, and pellets. Films can be used for dosage forms such as dissolvable films or transdermal patches. Pellets can be filled in capsules, punched directly into tablets, or granulated for traditional tablet production. Foamed pellets for fast-acting dosage forms are a novel development. Extruded rods and fibers are also being used as a dosage form.

Cutting extruded pharmaceutical formulations is often difficult because the polymers used are prone to fracture or smearing during pelletizing. Optimizing temperature and blade shape can help to solve cutting problems and minimize particulate generation, explained Bob Bessemer, sales manager for medical extrusion at the Conair Group, in his presentation. He noted that there are many technologies used in plastics extrusion that could potentially be applied to pharmaceutical extrusion. In wood-plastics composite processing, for example, extra sections are added to the end of the extruder to control cooling and thus improve cutting. He predicts that someday pharma manufacturers will be able to cut extrudate directly into tablets, once the problems of cutting and swelling are solved.

Borrowing another common plastics processing technique, tablets could also be directly injection molded after extrusion, noted other presenters. Looking to the expertise of the plastics industry may help propel development of pharmaceutical extrusion.