Heat wont sterilize it as much as you would think......
The best thing to do would be to use it as is, and once you have your brew made with at least 2% ba, filter through a .22um filter... .45 will work, but it is more for 'clarity' whereas .22 is for sterilization...
If all you have is a .45, you will still be alright as long as you add at least 2 % BA and let the finished product sit for 4-6 days before injecting....