If I imbibe the Toxicants tincture in Pathfinder, how long do the effects last, as nothing in the description gives any parameters for duration. Does it last forever, or is it similar to a mutagen, with 10 min per level?
I assume we are talking about the Toxicant Alchemist Archetype, correct?
If so, the duration of the effect is given on the description:
On a failed save, the target takes an amount of damage equal to the toxicant's Intelligence modifier. At 4th level, a target that fails its save must succeed at a second save 1 round later or take the same amount of damage again. This effect repeats as long as the target continues to fail its saving throws, to a maximum number of rounds equal to 1 + 1 for every 4 alchemist levels the toxicant possesses (to a maximum of 6 rounds at 20th level)
As for the duration of the ability, it does not have one, you activate or deactivate it as a Standard Action. When an archetype ability says it replaces an ability, it must have all rules regarding the new ability, as none of the old ability's rules are copied to the new ability.
In other words:
It's a new ability that does not carry over any rules from the ability replaced by it.
This ability replaces mutagen.