It's a good thing then, that a single dire rat isn't much of a problem for an adventurer either. With a mere 5hp and a 13 AC, it's likely to go down in one or two rounds at most. And with a mere +2 to attack, doesn't have a gat chance of getting through all but the weakest of armors with any frequency. Even the unarmored elf wizard has an even 50/50 chance of being hit.When you're carting a sword around and are armored from head to toe it's not nearly as much of a problem
Now a pack of dire rats, well that's another story. The again, a pack of pit bulls is too.
Again though, 4' 50lb rat, not your average US house pet.and another entirely to be threatened by a rat.
A 50lb rat is not mere vermin though. If you walked into your house and saw a 4 foot long 50 pound rat, you'd run screaming for the hills.They are not utter noobs, not commoners, and should not be threatened by vermin. The game is Dungeons & Dragons, not Cornfields and Cottontails.
I should also mention in general, something in regards to the dangers posed by a dire rats teeth. Rodent teeth in general, are very shap, more so than your dogs. A standard hamster can gnaw its way through metal if given time (I should know, mine did), now imagine that sort of shap teeth, made bigger, and given the strength of a 50 lb animal's jaw.