It's says it's a standard action. I'm not sure how I see the difference between " imbibing a mutagen" and "drinking a potion". It provokes attacks of opportunity, right?
That's a bit silly! There is zero difference between pulling out a potion raising it to ones lips and taking a swig and pulling out a mutagen raising it to ones lips and taking a swig! Omg did you see that alchemist swig that mutagen that's was amazing, supernatural even!!