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Mean Kinetic Temperature in GxP Environments

Vaisala Mean kinetic temperature

Regulatory bodies and stakeholder organizations in drug and device manufacturing and distribution have long been working toward creating standards for temperature monitoring that ensure the shelf life, quality and safety of products. In the last 15 years of these ongoing efforts, mean kinetic temperature (MKT) has been identified as one of the potential tools available for evaluating the impact of temperature on product quality.

MKT can be a difficult tool to understand and apply properly.  MKT was first proposed to guide stability studies, and is now considered as a tool for evaluating temperature excursions in the dynamic arena of Good Distribution Practices.  The math is difficult for most laypersons, and there is not a consensus on how MKT should be applied.

Regulatory Bodies and Definitions

The document most commonly cited in GxP-regulated industries for the definition of mean kinetic temperature is the International Conference on Harmonization (ICH) guideline: “Stability Testing of New Drug Substances and Products Q1A (R2).” The MKT definition from this guideline is shown above. The original purpose of the 1971 Haynes paper was to address the fact that climate-based temperature variation in uncontrolled pharmaceutical storage made it difficult to select a single temperature for use in product expiry testing.  Simply put, changes in storage temperatures can affect the rate at which products degrade.  Haynes sought to address this variation by calculating a “Virtual Temperature” for use in expiry testing that would take into account the expected temperature variability in a given region.  The equation he developed for “Virtual Temperature” is the same equation that is used today to calculate MKT.  It is based on the Arrhenius equation, which describes the temperature dependence of simple chemical reaction rates at ambient temperatures, where the rate of reaction generally doubles with every 10 degrees Celsius increase in temperature.

When establishing the temperatures for long-term stability testing of products to be stored at room temperature (RT) or controlled room temperature (CRT), the mean kinetic temperature in any part of the world can be derived from climatic data. The WHO divides the world into four climatic zones: temperate, subtropical, hot/dry and hot/humid, based on the drug stability research presented by W. Grimm (1985, Drugs Made in West Germany). Rules described in ICH Q1A (R2) are meant for climatic zones I-II (USA, EU and Japan).

The description for stability testing conditions in countries located in Climatic Zones III (hot and dry) and IV (hot and humid) can be found in ICH Q1F explanatory note and in the WHO technical report “Annex 2: Stability testing of active pharmaceutical ingredients and finished pharmaceutical products.”

In practice, products stored at controlled room temperature are often tested for long-term stability in simulated laboratory conditions of 25 or even 30 degrees (at 25°C ± 2°C/60% RH ± 5% RH or 30°C ± 2°C/65% RH ±5% RH) for dating purposes in climatic zones I-II, without using the exact calculated MKT value for this particular location. These temperatures are recommended by WHO in climatic zones I-II and (compared to the Haynes article) are probably high. They are an example of the worst-case scenario ideology often seen in the pharmaceutical and biotech industries. (For recommended long-term testing conditions all over the world, see the WHO Technical Report Series No. 953, 2009, Annex 2, Appendix 1 “Long-term stability testing conditions as identified by WHO Member States.”)

For another regulatory source that defines mean kinetic temperature, refer also to the FDA’s draft document: “Guidance for Industry, Stability Testing of Drug Substances and Drug Products.” This draft gives a much briefer definition: “Mean Kinetic Temperature (MKT) is defined as the isothermal temperature that corresponds to the kinetic effects of a time-temperature distribution.”

And, one last definition from U. S. Pharmacopeia (USP 35  Chapter <1150>, “Pharmaceutical Stability”): “MKT is a single calculated temperature at which the total amount of degradation over a particular period is equal to the sum of the individual degradations that would occur at various temperatures.

So, we have a basic understanding of what MKT is: a weighted non-linear average that shows the effects of temperature variations over time.

It’s the value used when planning the long-term stability study temperatures. The value includes the annual variations, e.g. lower and higher temperatures during winter and summer seasons. Thus, storage at a continuous temperature of 25°C during a real-time stability study includes the actual temperature exposure likely to be encountered under ambient conditions throughout Europe, NA and Japan, including real-time excursions from 25°C. However, the MKT is different than other weighted average calculations because it takes into account the non-linear effect of temperature excursions.

We can now see MKT as a mathematical tool to guide stability testing.  In support of this view, the FDA and European Commission regard the calculation as a tool to help determine storage conditions, especially for shipping and storing in specific climatic zones. (See also the European Medicines Agency document from the Committee for Human Medicinal Products (CHMP) “Guideline on Declaration of Storage Conditions” 2007.)

MKT may also have uses beyond stability testing.  In 2001 in a paper by J. Taylor of the Medicine Controls Agency, a different application for MKT was presented.  Taylor argued that MKT could be applied to evaluate temperature excursions in storage of actual products.  This was a landmark change in the application of MKT, providing industry with a tool to evaluate the quality impact of temperature excursions.

Taylor’s new MKT application was widely accepted.  It was a timely concept, especially in the light of the current regulatory challenges faced within Good Distribution Practices.  It should be noted that Taylor recommended caution in the application of MKT to evaluate temperature excursions.

The MKT value is supposed to encompass the total amount of product deterioration for a period of time that is equivalent to the incremental deterioration that would occur in separate excursions. However, the calculation is never to be used as a substitution for control and understanding of a controlled environment. Any temperature excursions must be rigorously investigated. A MKT value does not release us from this responsibility because a short-term spike still needs to be understood: it can indicate a larger problem, or a problem that may worsen. Root causes, as well as precise time and temperature data must be documented, and preventive actions then incorporated into a CAPA (corrective actions, preventive actions) management plan.

When & Where to Use Mean Kinetic Temperature

Because Vaisala’s Continuous Monitoring System software viewLinc calculates MKT, we are often asked how to apply the calculation. MKT was first developed and applied to ambient storage in warehouses, and our recommendations are consistent with this application.  We recommend using it for relatively stable, controlled room temperature environments during storage applications.  We do not recommend the MKT calculation for incubators and stability chambers, which are typically well controlled and not typically used for storage of finished products.  We do not recommend MKT for refrigerated or cold storage applications, as the degradation resulting from spoilage or phase changes are not well described by the Arrhenius equation. Nor is MKT ideal for long-term storage for the obvious reason that in any average over time, an increase in data points will eliminate spikes, such as a slowly climbing temperature that may indicate an equipment breakdown. A weighted, but non-linear average over time is best used when short excursions are less likely to cause serious harm (as in CRT) and over less time.  The calculation makes sense in storage and distribution applications, especially where there can be fluctuations – either because of the climatic zone, or the season.

It is not internationally agreed as to whether MKT is suitable for use in evaluating excursions during transportation and shipping.  For instance, the MHRA tells us that if the wholesale authorization holder can provide the marketing authorization holder with details of MKT, including the times and extent of any temperature deviations, this information may assist the marketing authorization holder in formulating advice to the wholesale authorization holder.  This clearly indicates that the MHRA supports the use of MKT in transportation.

In contrast, the German ZLG (Zentralstelle der Lander fur Gesundheitsschutz bei Arzneimitteln und Medizinprodukten/ Central Authority of the German Federal Lander for Health Protection Regarding Medicinal Products and Medical Devices) states that the mean kinetic temperature is not appropriate for use in a transportation risk assessment. Again, this is because the value does not account for effects that may lead to irreversible quality defects, even when certain temperature limits established during stability studies are exceeded only for a short time. The MKT value also does not account for finer points such as the possible formation of fissures in glass ampoules and injection bottles at temperatures near freezing point. Furthermore, calculation of the MKT requires that the temperature profiles of all previous transports are known, but usually these data are not available.

Ways to Calculate MKT

In its draft article for manufacturers, repackagers, and warehouses, the FDA recommends inserting all data points into the MKT equation directly. A minimum of weekly high and low readings is recommended, and more rigorous approximations using daily highs and lows, or even more frequent temperature readings, are also described. When calculating a yearly MKT, a minimum of 104 weekly high and low readings would be used. The yearly MKT should be calculated from the monthly MKT calculations. The FDA recognizes that, when the yearly MKT of a facility begins to exceed 25˚C, it may not necessarily have an impact on products marked with a CRT label that have been stored for less than one year at the time. Rather, this value should be taken as a warning that the facility may not be under adequate control.

It may be worth noting that many companies are moving away from using the term CRT in their operating procedures and documents. Many instead use a specific temperature range.

The USP 36 <1079> Good Storage and Distribution Practices for Drug Products dropped the use of CRT completely, as well as describing any other specific temperature ranges. USP now says that the control specifications should be unambiguous and not subject to interpretation. It may be that CRT will fall into disuse in quality documents and standard operating procedures in the near future. EMEA guidelines support the same ideology. The use of terms such as `room temperature´ or `ambient conditions´, is unacceptable.

 

Rules for Controlled Room Temperature:
Products marked with a CRT label should be stored at thermostatically controlled temperature at 20 – 25˚C (77˚F) and a mean kinetic temperature (MKT) calculated to be not more than 25˚C with excursions permitted to 15 – 30˚C (59 – 86˚F).
Brief exposure to temperatures up to 40˚C (104˚F) may be tolerated provided the mean kinetic temperature does not exceed 25˚C (77˚F). However, such exposure should be minimized.

 

The MHRA has stated: “It is not possible to obtain a meaningful MKT value from daily readings of simple max / min thermometers as temperature fluctuation is not a linear function. It is noted that some data loggers and building management systems are capable of recording multiple temperature readings over a time period and some offer the function of calculating the MKT over a given time period.”   The MHRA is clearly stating that continuous monitoring data can provide a more meaningful MKT value.

Regulations evolve with technology, and like many monitoring systems, Vaisala’s software viewLinc automatically calculates MKT, using every historical data sample. Simply select the timespan you are interested in and the MKT values will appear in the software window automatically (Figure 1).  Please note that mean kinetic temperature values alone should not be used in decision making when temperature excursions have occurred.  It is repeatedly mentioned throughout regulatory documents that information about the excursion duration and extent is required, as well as an evaluation of potential effects of the temperature excursion on product quality.

The MKT Calculation

The easiest and the most meaningful way to get an MKT value is by letting the data loggers and software do the work for you. It is of course possible to do the calculation yourself, but remember that you need an extensive amount of data and a calculation tool (e.g. Excel sheets). Otherwise the calculation can easily be overwhelming.  Furthermore, any tool used for calculation of MKT for use in GMP decision making would require validation.

The equation is:

The values used in the MKT formula are shown at right in the Equation Key.  It should be noted that ΔH, the activation energy, describes the reaction rate for the degradation of the active ingredients in a drug.  A default value of 83.144 kJ/mol is typically used as it is a good approximation for most pharmaceutical compounds.  Furthermore, it simplifies the math as it is numerically similar to the universal gas constant. Please note that it is possible to use a different ΔH value that is specific to a given product if the information is available.

If you want to see some simplified examples how to calculate the MKT, please check USP 35 Chapter <1160> “Pharmaceutical Calculations in Prescription Compounding.” Bear in mind that MHRA doesn’t support these kinds of calculations, nor does the FDA.

Equation Key
∆H = the heat of activation, which equals 83.144 kJ per mol (default value; unless more accurate information is available from experimental studies)
R = universal gas constant, which equals 8.3144 x 10-3 kJ per degree per mol
T1 = the (average) temperature, in degrees Kelvin, during the first time point
T2 = the (average) temperature, in degrees Kelvin, during the second time point
Tn = the (average) temperature, in degrees Kelvin, during the nth measured time point; n being the amount of the measured time points
TK = Result in degrees Kelvin. You’ll receive the final result MKT (in degree Celsius) by doing simple subtraction (TK – 273.15°K)

 

Conclusion

To summarize, we can make six basic recommendations for using mean kinetic temperature:

  1. MKT should not be used to compensate for temperature excursions in any application.
  2. When using MKT, ensure you have an adequate number of samples (time/ temperature).  The more samples that are included in the equation, the more the calculation will represent the actual MKT value.
  3. MKT should not be used in areas where temperature is not well controlled.
  4. Use MKT only if the storage temperature specified on the label of the product does not exceed 25˚C.
  5. MKT should not be used for products that require controlled low temperature.
  6. Regardless of whether you use the MKT calculation or not, all temperature excursions should be investigated.

We hope that this exploration of the history and application of MKT is useful. This topic, and its applications in distribution, will likely continue to evolve as guidance, regulations, and technologies progress.

 

References

  • European Medicines Agency, committee for human medicinal products (CHMP), “Guideline on Declaration of Storage Conditions:
    • In the product information of Medicinal Products
    • For Active Substances”, CPMP/QWP/609/96/Rev 2, 2007.
  • European Compliance Academy (ECA), GMP News 07.05.2014: “GDP Question: When to use Mean Kinetic Temperature Calculation (MKT)?”
  • European Compliance Academy (ECA), GMP News 22.04.2015: “GDP: Is temperature control required for each Transport?”
  • FDA, Draft Guidance, Stability Testing of Drug Substances and Drug Products, 1998.
  • ICH Harmonized Tripartite Guideline, Stability Testing of New Drug Substances and Products Q1A (R2), 2003.
  • ICH Q1F, Explanatory Note on the Withdrawal of ICH Q1F on the ICH Website.
  • J. Pharm. Sci., 60:927-929, 1971. John D. Haynes. Worldwide Virtual Temperatures for Product Stability Testing.
  • The Pharmaceutical Journal (vol 267), July 2001. J. Taylor. Recommendations on the Control and Monitoring of Storage and Transportation Temperatures of Medicinal Products.
  • USP, Chapter <1160>, Pharmaceutical calculations in prescription compounding.
  • WHO Technical Report Series No. 953, 2009, Annex 2, Appendix 1 “Long-term stability testing conditions as identified by WHO Member States”.
  • WHO Technical Report Series, No. 953, 2009, Annex 2, Stability testing of active pharmaceutical ingredients and finished pharmaceutical products.
  • “Drug Stability Testing – Classification of countries according to climatic zone” Drugs made in Germany, by Dietz, R., Feilner, K., Gerst, F., Grimm, W.
  • USP 35 Chapter <1150>, Pharmaceutical Stability
  • USP 36 Chapter <1079>, Good Storage and Distribution Practices for Drug Products

 

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