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FDA: thermocouples useful in development but have limits as commercial controls
Summary
CDER's Steve Ryu said thermocouples are valuable in development to monitor vial temperatures but can misrepresent batch behavior and create contamination risks; he recommended careful selection and validation of PAT tools.
Steve Ryu described thermocouples as a straightforward direct-measurement approach: "You stick thermocouples directly into some of your vials to monitor product temperature during the cycle and identify the endpoint of drying." He cautioned that thermocouples can act as nucleation sites that change freezing behavior and are not fully representative of the batch, and that their insertion raises contamination risks unsuitable for routine commercial use.
Ryu also discussed comparative PAT methods — Pirani gauges and capacitive manometers — explaining why readings diverge during primary drying and warning about calibration and robustness challenges for these sensors. He advised manufacturers to "choose the right strategy for your specific product and process and then validating it works."
