Published: 3 March 2016

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Medicine Expiry Dates – What They Don’t Tell You

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Prescriber Update 37(1): 4-5
March 2016

All medicines have a defined shelf-life or expiry date

One of the most common questions asked by patients is whether a medicine can be used past its expiry date. The short answer is no. Heat, air, light and moisture can impact the effectiveness and safety of a medicine. The shelf-life or expiry date of a medicine is the length of time it has been demonstrated to stay effective and safe when protected from these elements. Use of a medicine past its expiry date may result in a lower dose of active ingredient than that stated on the label (particularly relevant to antibiotics) or an increased risk of microbial contamination (for medicines containing preservatives such as eye drops).

The expiry date is determined from stability studies

As part of the medicine approval process, Medsafe evaluates data from stability studies performed by the manufacturer. The purpose of stability testing is to gain information on the effect of changes in environmental factors such as temperature, humidity and light on the quality of the medicine over time. The data generated in these studies is used to identify the optimal storage conditions for the medicine in its original container and to assign an expiry date.

The expiry date is specific to the original container

Depending on the medicine, expiry dates may be set for a fixed time after manufacture (unopened) and also during use (opened), but are specific to the container used in the stability studies. Different packaging affords different protection, such as the inclusion of desiccants in containers to trap moisture and enhance stability. Additional studies carried out on the medicine outside its immediate container, or in other packaging materials, are performed at the discretion of the manufacturer. Healthcare professionals are advised to refer to the Pharmaceutical Precautions section of the medicine data sheet, available on the Medsafe website (www.medsafe.govt.nz/Medicines/infoSearch.asp), for all storage conditions and expiry dates supported by stability data.

How a medicine is stored will affect its expiry date

Many medicines are repackaged into individualised dosage systems, such as blister packs, to aid medication adherence and safe administration. When a medicine is repackaged, its characteristics may change in ways that have not been evaluated during the approval process (further information can be found in this edition and in a previous edition of Prescriber Update¹). Consequently, the manufacturer’s expiry date no longer applies and a pharmacist may affix a new expiry date that is shorter than that originally set, to account for these variables.

The stability of some medicines will be further influenced by where they are stored at home. In New Zealand this is commonly bathrooms and kitchens, which can suffer extremes of temperature and humidity. Patients should always be advised to store their medicines as recommended on the label, and to discard the medicine after the expiry date.

References

1. Medsafe. 2014. Medicine Storage – An Uncontained Issue? Prescriber Update 35(3): 36-37. URL: www.medsafe.govt.nz/profs/PUArticles/September2014MedicineStorage.htm (accessed 21 January 2016)