Mean kinetic temperature (MKT): what it is and when to use it
MKT is a single temperature that represents the cumulative thermal stress of a varying temperature history, weighted by the Arrhenius relationship. It is useful for storage assessment, not for hiding excursions.
Mean kinetic temperature is the isothermal temperature that would produce the same degradation as the actual varying temperature over the period, assuming Arrhenius kinetics. Because reaction rates rise exponentially with temperature, MKT is always at or above the arithmetic mean.
The calculation
MKT = (ΔH/R) / −ln[ (Σ e^(−ΔH/RT_i)) / n ], with T_i the absolute temperatures of the intervals, R the gas constant, and ΔH the activation energy — 83.144 kJ/mol by convention in ICH Q1A(R2). It should be computed from the actual monitoring data, not from daily averages.
Use and misuse
- Appropriate: characterising the long-term storage condition of a warehouse for comparison with the labelled storage condition.
- Inappropriate: arguing that a brief 15 °C exposure of a 2–8 °C product 'averages out'. Product-specific excursion data govern that decision.
Frequently asked questions
- Is MKT the same as an average?
- No. It is a weighted value that gives more weight to warmer periods, so it exceeds the arithmetic mean whenever temperature varies.
References
- [1]ICH Q1A(R2): Stability Testing of New Drug Substances and Products
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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