The method to calculate the expiry date of drug after opening the container.

Question: I want to know the stability and sterility of K-Y jelly after it is opened to use, and how long can K-Y jelly be stored at room temperature after opening?

Answer: K-Y jelly is a topical emollient formulation. The expiry date is  defined by the next six months after opening.

But another way to calculate an expiration date is beyond use date. Beyond use date is the date that pharmaceuticals should not be used anymore. The beyond use date of pharmaceutical packaging or after opening to use, is calculated from 25% of the rest from the date of opening the container until the expiration of pharmaceuticals in the original container labeled by the manufacturer.

Pharmaceuticals are generally defined to expire six months after opening the container. But the method which gives the shorter expiry date generally should be selected to determine expiry date more than another method.

Example: Expiration date on the label that is defined by manufacturer is December 12, 2015. Date opening medication is December 12, 2014. The period from December 12 2014 to December 12, 2015 was a period of 12 months and 25% of 12 months is three months, so the expiration date should actually be three months from the date of opening the container, or it was April 12, 2015. 

However, if pharmaceutical has changed from the original product such as color, smell and viscous. This may be due to improper drug storage. It makes the drug loses it's stability. Therefore the drug should not be used anymore, although it has not reached the calculated expiration date.

Reference:

1.Karpinski JP. Medication expiration dating. PharmacyTech News. 2011. Available onhttps://www.cedrugstorenews.com/userapp/lessons/page_view_ui.cfm?lessonuid=&pageid=98A4D0865060D9CDE96A50282801AE4D
2.Gennaro AR, editor. Remington: the science and practice of pharmacy. 20th ed. Philadelphia: Lippincott Williams & Wilkins; 2000.

3.Authority of the United States Pharmacopeial Convention. The United States Pharmacopeia, the national formulary: USP 23, NF 18 1995 / United States Pharmacopeial convention. Rockville (MD): The United States Pharmacopeial convention; 2000.