How to factor in reduced damage for Coup De Grace?

Question

In a game I played recently, a character coup de graced a natural lycanthrope. The damage was not enough to out right kill him, but it still forced a save to resist death, as per coup de grace.

Now, my question; Do Damage Reduction and other similar effects lower the DC for the fortitude save?

We weren't sure at the time, so we tried to look it up. Neither DR nor CDG address this issue. The only thing that I can find on it is that the DC for the fort save is based off of the damage dealt, where as DR describes the effect as ignoring damage. This would make me think that, even though the damage is ignored, mechanically it was still dealt, thus it would factor into the save DC. However, I could be wrong.

All advice and experience is welcome, however I'm looking for an answer that can site a source for proof. I can see this argument going either way, and if possible, I'd like to get something official to end it.

Answer 1

I would argue that this is pretty clear. CDG says:

If the defender survives the damage, he must make a Fortitude save (DC 10 + damage dealt) or die.

DR says:

The numerical part of a creature's damage reduction (or DR) is the amount of damage the creature ignores from normal attacks.

Clearly, DR reduces damage dealt.

Furthermore, DR says:

Whenever damage reduction completely negates the damage from an attack, it also negates most special effects that accompany the attack, such as injury poison, a monk's stunning, and injury-based disease.

So, not only would DR lower the DC of a CDG. If the DR were high enough to negate all damage, I would rule that the CDG would also be negated.