The Pharmaceutical Journal Vol 267 No 7173 676-680
10 November 2001

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Letters to the Editor

Medicines storage

What about "worst-case" conditions?

From Dr M. J. Shott, MRPharmS

In his article (PDF* 60K) on storage temperatures for medicines (PJ, 28 July, pp128–31), John Taylor of the Medicines Control Agency explained the use of mean kinetic temperature (MKT) and stated that products could be allowed limited excursions between 15 and 30C. Grimm's calculation¹ of 25C as the MKT for sub-tropical and Mediterranean regions (climatic zone II) assumes the daily temperature reaches 36C for four hours a day, and 32C for six hours a day, for two months of the year, as well as 31C for four hours a day for a further four months. If a product is stability tested at 25C then the MKT concept allows us to conclude that it may be stored under normal conditions throughout Europe for the period of the stability test. However, licensing authorities currently require it to be labelled "Do not store above 25C", although considerable deviations above 25C and even 30C are justified.

These considerations are based on mean rate of decomposition, and some products might be more damaged by high temperatures (for example, melting) than simple reaction kinetics suggest. However, these changes would be identified by the short-term high temperature storage required under International Committee on Harmonisation (ICH) stability guidelines and should lead to additional labelling requirements.

In these circumstances, labelling a product "Do not store above 25C" seems confusing because it is not literally necessary. It is in any case impractical, because even in the United Kingdom temperatures frequently exceed 25C and air conditioning remains rare in patients' homes, community pharmacies and warehouses. The decision within the ICH and the Committee for Proprietary Medicinal Products to replace vague directions such as "protect from heat" with directions including numerical temperature limits was understandable. However, this leads to labelling which is unhelpful to consumers and professionals. I believe consideration should be given to interpreting conclusions from stability storage trials only as storage directions meaningful to the consumer which require specific actions (such as "refrigerate below 8C"). A product should only be marketed in a country without such a direction if it can be stored at the appropriate MKT for the climatic region. If considered necessary the region could be indicated on the pack, or perhaps the MKT could be given as an "average" storage temperature. Good practice should require manufacturers, wholesalers and perhaps even pharmacies to show that the storage conditions do not exceed the worst case considered by Grimm.

Martin J Shott
Innovata Biomed Ltd
St. Albans,
Hertfordshire

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