What happens if I accidentally took a double dose?

My husband took two of his Keppra at once

Hello
If I am understanding your question correctly your husband was prescribed one keppra pill per day and he accidentally took 2 at the same time.
He will be okay. Luckily keppra does not cause marked drowsiness nor does it have any serious/acute side effects.
However, I would advise your husband to drink a lot water, especially during the next 12 to 24 hours.
Lastly, it would be a good idea to notify your physician who prescribes the keppra. Just inform your physician that he accidentally took two pills at once by mistake.
Take care!
bestpup