TOPIC:

I have a bottle of Himalayan rock salt that expires on 29th Jan 2017.

Given that this rock salt has been hanging around for the last 250 million years, how does the act of putting it in a bottle cause it to go off within a couple of years?

The answer is it does not, it simply relates to our food and medicine packaging protocols.

When a manufacturer makes a new drug they need to make it up in a convenient form - usually tablets. Tablets have a Jekyll & Hyde personality requirement. Stick together in the bottle, fall apart fast in water.

Once an initial batch of pills has been made they undergo what is know as rapid stability testing and it's really the stability of the tablets we are looking at. In the rapid stability testing they are warmed and cooled, humidified and dehumidified, exposed to light, etc to simulate daily use. 3 months testing gets you a 1 year shelf life, 6 months testing gets you a 2 year shelf life.

The current Sovaldi in use in Australia has an expiry of 9/2016 suggesting it was made 9/2014.

Almost all drugs are good for decades after their nominated shelf life has expired. If you're interested to read more:

www.fda.gov/EmergencyPreparedness/Counte...mework/ucm411446.htm

Having worked in the food industry with businesses that comply with FDA protocols I'm aware that often shelflife labelling is based on a decision process that does involve the legal requirement to nominate some sort of date in addition to accelerated plus retained sample testing which both allow that the item may not be stored ideally during whatever shelflife is given.
In that industry shelflife extensions occur but more so for ingredients and intermediates than finished saleable products (the latter is often just a marketing decision). The better operators who are FDA compliant have processes to evaluate these items on a case by case basis and then approve a decision to extend, usually with documentation and/or relabelling that indicates both new shelflife and that an extension was given.

Is there a similar process within the pharmaceutical industry? Alternatively, how do we know that the drug involved is still known to be safe/effective rather than something that slipped through due to a human error?