Tuesday, 12 September 2017

Regulators raise concern with rapid method validation

In July 2017 Sage Products Inc. received a warning letter from the U.S. Food and Drug Administration (FDA). Within the warning letter was a concern about the implementation of rapid microbiological method, where the method had been used to replace a compendial method.

In the warning letter, the FDA state “Your firm failed to establish and document the accuracy, sensitivity, specificity, and reproducibility of its test methods.” This relates to the use of a rapid method.

Specifically: “You use the (b)(4) method to screen for microbiological contamination in drugs produced entirely at your facility and those manufactured under contract. This (b)(4) screening method (b)(4) for microbiological examination of your liquid drug products is not adequate for its intended use. You attempted to validate your (b)(4) microbial detection method, but were not able to demonstrate that it could reliably and repeatedly determine whether objectionable microorganisms were present in your drugs.”

The FDA are concerned about the comparative findings from the USP method and the replacement rapid method: “After receiving three consumer complaints for discoloration of this product, you initiated testing of your retains using both the modified U.S. Pharmacopeia (USP) microbiological limits method and the (b)(4) method. Both analyses found microbial contamination. Notably, the USP modified method (b)(4) found an exceedingly high microbial count of over 57,000 CFU/ml, and also identified Burkholderia cepacia, an objectionable microorganism, in this product lot.”

It seems that the firm elected to run with the results from the alternative method, despite the USP method finding an objectionable microorganism. This led the FDA to state: “Had your firm been utilizing a screening method capable of consistently detecting B. cepacia, these products may not have been released in the first instance.” Part of the reason was “because [the company] failed to include B. cepacia on the list of objectionable organisms.”

The use of the alternative method had also gone against FDA advice: “FDA informed you that your (b)(4) method (b)(4) has not been adequately validated for detecting the presence of microorganisms, including the presence of B. cepacia. In a subsequent meeting on November 30, 2016, FDA advised you to use a verified compendial method for all bulk drug solutions and finished product microbiological testing until you could further assess the suitability of the (b)(4) method.”

The concerns the FDA had with the rapid method were:

“It specifies a (b)(4) dilution factor. USP <62> requires a 1:10 dilution factor. Your dilution factor is (b)(4) times greater than the USP method and provides insufficient detectability to rule out the presence of objectionable microorganisms and unacceptable total counts.”

Furthermore the rapid method it not account for the enrichment step called for in USP <62>. Also “it does not include the scraping step during sample preparation, which your submitted laboratory data indicates is required to validate organism recovery.”

There was also a comment about the use of stressed organism as part of method validation (a controversial point within pharmaceutical microbiology): “it lacks evidence that small numbers of various microorganisms, including those that are injured and stressed, can be reliably recovered. Specifically, sample effect (defined by your firm as the inhibitory effect of a sample on the growth of various microorganisms) data for B. cepacia was collected using a fresh-grown culture, not a stressed organism.”

The final charge was that the method validation did not “establish potential sample interference factors (e.g., enhancing or quenching) for each product formulation.”

There was also criticism about the sampling and sample plan used to ensure the tested sample was representative of the lot. There was also concern that the replacement method, unlike the USP method, did “not provide for potential speciation of the detected microbial contamination in the (b)(4) initial screening test.”

The implications from the FDA letter, as well as signaling a pertinent lesson when implementing a rapid method that needs to be equivalence to or better than the rapid method, are:
  • Does the validation of methods require the use “stressed” organisms?
  • Does validation always need to be against each product formulation (not just the strongest concentration of the most inhibitory ingredient)?
  • How are representative samples built into the validation process?
  • Does a list of objectionable organisms need to be prepared ahead of the method validation? Or is this just a B cepacia issue?

If you have views on this, please add a comment.

Thanks to Nigel Halls for the heads-up about this warning letter and its considerable implications.

Posted by Dr. Tim Sandle