How does storage temperature relate to expiration date?

Most of our ibuprofen samples recommend storage at 20-25 C (68-77 F). As far as I can tell, most of them have a shelf-life of 3 years, which means that the expiration date should be 3 years from the date the pills were manufactured.

I can say that at Pfizer, when we set an expiration date, we tested the pills as they were stored for some length of time (for example, 3 years) and if they passed all of the quality tests, we set an expiration date of 3 years. That does not mean that they were of poor quality after 3 years - we just stopped testing them at that point. So, are your medicines still OK after the expiration date? Well, the answer is, it depends. I would be more wary of prescription medications after their expiration date than medicine I bought over the counter, but the best answer is, throw it away after its expiration date.

The expiration date is directly related to the recommended storage temperature. Anyone who has taken chemistry knows that one way to speed up a reaction is to heat up the sample. So if the medicine is "expired" after 3 years at room temperature, it will be "expired" quicker at a higher temperature.

The relationship is given by what is called the Arrhenius equation:

k = Ae^(-Ea/RT)

But, let's skip the math and get straight to the answer: If a medicine has 36 months of shelf life at 20-25 C, it has 30-40 days of shelf life at 70C. Roughly, you can half the shelf life for every additional 10 degrees Celsius.

Remember, these are rough estimates, but you can see:

20C: 1080 days
30C: 540 days
40C: 270 days
50C: 135 days
60C: 68 days
70C: 34 days

For those of you interested in the math:
A good average value for Ea of this type of reaction is 15 kcal/mol (according to the pharmaceutical experts). The range is 12-18 kcal/mol.