The trouble with "Save VS. poison, or die" rule

I have been looking for a mod for the "save VS poison, or die" rule.  I think this it is pretty silly that a a centipede can kill a higher level adventurer,  almost as easily as a 1st level adventurer.

I ran across a mod somewhere, (I'm not sure where) which changed the poison save from a "save", and instead made it a d6 d4 worth or additional damage, for a certain number of rounds.  I don't remember what the exact mod was, but I have enough of a framework, to make something useful out of it.

Here is what I am thinking.

• Roll save vs poison as usual.
• Save = No damage, or as otherwise indicated by specific rules for type of poison, or monster.
• Fail = Take 1d6 1d4 points of damage per turn, for X number of turns, with X  = the HD of the monster.  Less than 1 HD monsters round up to 1.   Example:  The poison from a 5HD Giant Spider, will do an additional 1d6 1d4 points of damage each turn, for 5 turns, beginning on the turn after the wound was received.
• Previous rule applies, if poison runs over to CON damage. 

At first, this may seem to be a bit light, when compared to the extreme result of death; but, consider that this is continuing damage.  Initially the character may take 1-4 points of damage for the delivery of the poison, but the next turn, and subsequent turns, will take an additional 1d6 1d4 points of damage - in addition to any other damage taken from other attacks/effects.

This gives the character a little bit of wiggle room when facing envenomed creatures, but still faces them with the possibility of death, through continuing damage.

We have not tried this out yet, but I think it will work ok...at least it does in my head. 

I will get you..... in about 5 turns!