Although more units are being sold, Peterson and Ranpuria say the average size of the vessels has decreased as drug compounds become more active. However, the need for control systems, containment and cleaning, for example, has increased.
Suit your application
The agitated filter dryer is not suitable for every application, however. “Amorphous products are hard to deal with in any filter,” Fabricius says.
Those who use the equipment also say it has a couple shortcomings. For the most part, they indicate they can get around such issues once they are identified.
Gary Hedden, Palo Alto, Calif.-based group leader of process development for Roche Pharmaceuticals, says there are two small filter dryers in his lab: a Rosenmund machine, purchased circa 1993, and another from PSL, vintage 1999. Both are used for developing pharmaceuticals and are rarely used to process the same thing twice. “After CIP, we always have to take the filter dryer apart to get the last bit of material that is stuck in the filter media and in the O-ring groove,” Hedden says.
Eastman’s Suggs says they used to have problems with material getting lodged around the O-ring at the side-discharge valve; he now specifies a higher-grade O-ring that provides a better seal to avoid such problems. Since 1998, Eastman has purchased four agitated filter dryers from Rosenmund/De Dietrich that range in size from 6 m² to 12 m²; these larger vessels do not have CIP systems. “Since we often process the same chemical for several runs, it’s sufficient to manually wash the bottom filter plate with a hose,” he says.
Bristol-Myers Squibb’s Heit and colleague Tom Mitchell, a senior research scientist, have seven filter dryers in their care. The company has six vessels from Rosenmund that range in size from 0.03 m² to 1.5 m², as well as a 0.28 m² unit from Pfaudler (another unit from the company is on the way). Heit says the vessels are used in the pilot plants for process development and producing drugs for clinical trials. Since the filter dryers are used for a different product every time, “we spend as much time cleaning as we do processing,” Heit says, even with the CIP systems.
“The filter dryer can become a bottleneck since you are combining two unit operations into one unit,” Lilly’s Abhinava says. “We usually use it when filtration and drying rates are sufficiently fast in order for the filter dryer not to be a bottleneck.”
Ranpuria says that although the filter dryer might limit throughput, “it is more cost effective as one single unit, thereby simplifying manufacture and removing complexity while minimizing product handling steps, reducing potential cross-contamination during handling, and saving analytical time.”
Heit and Mitchell say they would like for filter dryer vendors to offer a more complete package that includes glove boxes or other systems for removing the product, adding that PSL is leading in such offerings. “The mechanisms for getting material in and out, and for cleaning the vessel should be resolved at the vendor level, not onsite,” Heit says.
Fabricius says Pfaudler is making progress toward offering such a package: The company is working with outside vendors to provide isolators, such as gloveboxes, as well as other technologies to ease product handling.