Change antibiotics?

I started taking my first amoxicillin tablet last Thursday evening. I've already taken 10 (twice a day). The pack is now empty because the pharmacy has run out of tablets. I have another pack of amoxicillin tablets that's been closed, but from a different manufacturer. Can I still take them? Because there are two different manufacturers, and my ENT doctor prescribed 1000 mg, and these are 875 mg. The doctor said I can take them as they are, but I'm still unsure.