Limitations of Conventional Mixing Systems in Pharmaceutical Topical and Transdermal Drug Product Applications

The inherent nature of high-viscosity pharmaceutical drug products poses real operational challenges to manufacturers. To succeed, processors must seamlessly combine safe and precise ingredient loading, powerful and durable blending, and sterile and efficient cleaning within their operation. Some manufacturers have found it difficult to solve these challenges due to limitations of conventional mixing systems.

Here are some of the most common issues with conventional mixing systems in pharmaceutical and other high-viscosity product settings.

Separate, dual mixers may deliver insufficient and inefficient agitation

Many high-viscosity products require two kinds of mixing action. Manufacturers sometimes attempt to achieve this mixing action by using slower-moving scrape surface agitation and a separate top-entry, high-shear mixer.

This design presents some problems. A mixer with this configuration offers limited mixing action due to the reduced number of bars. In turn, this increases mixing time and can leave pockets of unmixed ingredients throughout the vessel.

Processors may try to overcome this inefficiency by using two separate mixing vessels to handle their high-viscosity products. Two mixers, one with a high-shear mixer alongside another with a double-motion scraped surface agitator, mix high-viscosity products in a two-stage process.

Though it could conceivably handle more product, this two-stage process is inherently inefficient. It requires additional processing time to move product from one vessel to another in addition to the transfer lines and pumps necessary to make the transfer in addition to complicating the cleaning requirements. FDA regulations can also complicate a two-vessel mixing operation. Use of multiple vessels and product transfer steps may require additional regulatory approval to keep the process fully compliant.

Recirculating high-shear mixing systems can be difficult to clean, expensive

Recirculating high-shear mixing systems can present an intriguing alternative to multi-vessel solutions. These high-performance systems constantly recirculate the product through a high-speed mixing apparatus and can mix products to sub-micron consistencies.

However, recirculating shear systems require additional external components and a product transfer recirculation loop, which are limited to lower viscosities and can potentially complicate clean-in-place (CIP) requirements. Typically, they are also more expensive than vessel-based mixing systems.

Bottom-entry shear mixing systems can reduce heat transfer surface area

A final conventional solution to the challenges of high-viscosity product mixing is the bottom-entry shear mixing system. These mixing systems introduce the shear mixer at the lowest point in the vessel, optimizing batch potential.

However, the penetration of the mixer in the bottom of the vessel eliminates heat transfer surface area in a portion of the vessel. This setup also requires clearance from other agitation, limiting its ability to fully scrape the vessel. Limited scraped-surface agitation can impact heat transfer, in turn leading to potential unmixed and uneven heating/cooling of product on the jacketed vessel walls.

How Lee meets the challenges of high-viscosity mixing

The issues with conventional dual-agitation vessels, multi-vessel mixing systems and complex single-unit systems like recirculating- and bottom-shear mixers still leave the industry searching for a solution. The unique design of the Lee Industries Tri-Mix Turbo-Shear mixing system addresses all these drawbacks, handling high-viscosity products in a single customized configuration to meet a wide variety of process requirements.

To learn more about how this system could work in your manufacturing setting, download Mixing Topical Ointments, Gels and Lotions in High-Viscosity Applications from Lee Industries today.