Buprenorphine

My cat smokey got hurt an they gave him Buprenorphine but he had some left over and i saved it... now he has a hurt foot that will do fine on its own but he is hurting and i want to give him the left over Buprenorphine that I have to help manage his pain... but I need to know how long can you save the left over syrenges of oral Buprenorphine and still be able to use??? I don't want to give him bad pain med and need to know how long after you get it can he still use it??? thanks for any help on this  

If it were me I would call the vet's office and ask them.  I know you don't want to involve the vet because you don't feel he needs to be seen and he may not need to be.  When it comes to medication though your vet is the one to ask.