Controlled Room Temperature (CRT) MKT Calculator

CRT per USP/ICH is 20–25 °C with a not-to-exceed MKT of 25 °C and transient excursions allowed between 15 °C and 30 °C. The authoritative limit is whatever your product's labelled storage condition and stability data specify — read it off the marketing authorisation, the manufacturer's storage statement or the governing pharmacopoeia, and enter your real temperature history against it.

Temperature-map the room to find the worst-case (warmest) location across representative conditions including a hot spell, then monitor that location continuously. Compute the MKT over the qualification period from that worst point: if it stays ≤ 25 °C with no excursion outside 15–30 °C, the room meets CRT. Document the mapping, the worst-case point, the monitoring data and the MKT calculation — that package is what storage qualification and a GMP auditor expect. Re-assess seasonally; a room that passes in spring may need attention in peak summer.

Because degradation is not linear with temperature — it accelerates roughly exponentially (Arrhenius). A simple average treats an hour at 30 °C the same as an hour at 20 °C either side of 25 °C, but the product is harmed far more by the hot hour. MKT weights each reading by exp(−ΔH/RT), so it reflects the true cumulative chemical stress. It is always ≥ the arithmetic mean, and it is the figure regulators expect for storage and distribution compliance.

Use a representative series with durations — typically the logger's interval readings, or summarised blocks of 'X hours at Y °C' if you only have an excursion summary. The more granular the data, the more accurate the MKT, but the result is dominated by the warm excursions, so capturing those accurately matters most. Don't average data before entering it — that defeats the point; enter the temperatures and let the calculator do the kinetic weighting.