How can i get my dogs to relax and let me trim their nails?

my dogs get so freaked out when getting their nails trimmed, i don't even bother anymore. now their nails are so long, they actually are preventing them from walking correctly, they can't even get traction on my tile floor. can i give them a xanax to relax them or will i kill the dogs? one is 35 lbs and the other is 27 lbs.