my dog was accidentally given 5 times the mg prescribed of prednisone.  he weighs 100 lbs .  do you think he will be alright?

Assuming you're talking of the steroid Prednisolone and have mis-spelt it.  Yes it is possible to overdose on ANY drug...though the reactions will be different....best thing to do is seek the advice of a vet, who may well advise to rest the dog completely and not allow it to get stressed or excitied in any way for a good couple days...

My friend overdosed my old cat with his heart tablets...he was only meant to get a quarter of a tablet, but she mis-read my note and gave him 3/4 of the tablet...he was fine, but had to keep his stress-free for 24hrs after.

Prednilisone is a steroid and has long term side effects and some short ones too.

However one instance of OD is unlikely IMHO to have any detrimental effect.