We've used antibiotics that expired as far back as 2001 before and it still worked and fixed the problems. It was Spectam or LA 200 I believe that we were using that was expired that long. That stuff is to expensive to throw out even at 5 years past expiration date. I would bet the stuff nowadays is still good almost 15 years or maybe even more after expiration. I would use it until its gone or until you notice its not being effective.
I also think the back rub would be a good idea as well if your nervous about it.