E-drug: Expiry dates of drugs
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Dear Dr Srinivas,
A major factor determining expiry dates is related to how long the
manufacturer wants to carry on the stability tests. These tests are
time consuming and can therefore be expensive... So often a
manufacturer decides, after x months, that it has been enough. If at
that time (i.e. after x months) the product is still in good enough
shape, the manufacturer will use "x months" as shelf life (how many
months after "x" the product would still be OK is not of major interest
to the manufacturer). The value of "x" however is often quite arbitrary
and may vary between manufacturers (hence the variation between
similar products from different manufacturers).
Having said that, in a number of cases (i.e. with 'critical or sensitive
products') the indicated expiry date really does indicate that the
product is not suitable for use any more after that date (though
storage conditions usually have more influence than time per se).
Then, different inactive ingredients can also have an influence on
expiry dates - though I don't think there are many general rules here.
But esp. for tablets, the 1st reason I mentioned is much more
frequently the actual factor determining expiry date than most people
realize.
Hope this is useful.
Karin Timmermans
WHO Indonesia
Email: Karin@who.or.id
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