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Frequently Asked Questions

 6. What is the safety concern threshold (SCT)?

The SCT has been defined by the PQRI guidance document 'Safety Thresholds and Best Practices for Extractables and Leachables in Orally Inhaled and Nasal Drug Products', as the threshold below which a leachable would have a dose so low as to present negligible safety concerns from carcinogenic and noncarcinogenic toxic effects.

The SCT is an absolute exposure, expressed in terms of total daily intake (total exposure per day). It must be converted into a relative amount, expressed in terms such as the amount of an individual leachable in a particular product (e.g. µg per vial in a parenteral product or µg per bottle in a e-liquid product), to be useful to an analytical chemist conducting extractables and leachables studies. This conversion is performed by using information on the product configuration such as

  • the number of doses per vial

  • number of vials per day

  • number of mLs per dose

  • number of mLs per day

  • etc....


The converted SCT, which should be used by the analytical chemist is called the Analytical Evaluation Threshold (AET - see Q7).

The SCT can be applied to the majority of potential extractables and/or leachables, however there are a number of classes of compounds that have lower SCT values e.g. N-nitrosamines, PAHs, PNAs. Compounds such as these require special consideration due to their associated toxicities, and need to be evaluated by more specific and sensitive analytical techniques.

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