At the time of the yield investigation, the marketing authorization application had been submitted for approval to the Medicines Control Agency (MCA) of the UK. There were communications between MCA and Baxter to finalize the product specifications. The 100 kDa membrane yield problem and the 50 kDa membrane change proposal were communicated to the MCA and the change proposal was accepted.

Table 4. Results from production lots after 50 kDa membrane implementation

The size of the GCMP after 100 kDa processing was evaluated as part of the low yield investigation. Based on absolute MW determination by laser light scattering, the MW of GCMP was determined to be 200–300 kDa. A rule of thumb in UF is that the membrane of choice should have a NMWCO one-third to one-fifth of the MW of a product that is to be retained.⁹ According to this rule, if GCMP sizing data had been available during process development, the 50 kDa membrane would have been a better choice than the 100 kDa membrane.

Throughout the production history, the 50 kDa UF membranes have been reused up to 11 times. Other UF steps have reused UF membranes for up to 26 cycles. Most of the time, UF membranes are retired because they exceed our internal specification of 24-h dirty membrane hold time. Most of the NWP values following cleaning appear to be stable. Because meningitis vaccine purification involves multiple UF steps and each UF step uses multiple UF membranes cassettes, the ability to reuse UF membrane represents a substantial savings in production cost.

CONCLUSIONS

The key lesson learned from the UF yield investigation is that in designing a UF process and validation program, one should consider the sensitivity of the desired separation to variation in the retention profile of different lots of membrane.¹¹ In this case, the UF step was used for concentration and purification of GCMP. The impact of membrane variability on product yield was significant. The impact of this variability on product yield and purity should be evaluated as part of process development and confirmed during process validation.

Shwu-Maan Lee, PhD, is a technical director, Bob Kruse, PhD, is a research scientist, and Amy Robinson, PhD, is a senior research manager, all at Baxter Healthcare, Beltsville, MD, 301.419.8587, lees4@baxter.com
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