Contact a Doctor and get a new RX for an antibiotic if he thinks you need one. Not taking antibiotics properly causes resistant strains to form which then leads to us not having antibiotics to treat bacteria because they all eventualy become resistant.
You definetly shouldn't use it. Once drugs are expired not only do they lose their strength but they can change their chemical compounds.
Plus, if the antibiotics were originally prescribed for a different infection, say bronchitis and you are now trying to use them for, say an infected cut they probably wouldn't work. Different antibiotics are only effective against certain germs. You should consult a doctor.
So you have a prescription that was filled at least a year ago. At the time it was filled it was good for one year, which means if it has been EXPIRED for a year then the pills are actually at least 2 years old. I would not recommend taking it. In fact, using them even if they are weakened can cause the bacteria causeing your infection to become RESISTANT to and stronger than the medication. This means, the infection could come back worse and the antibiotic might not work at all.