Unofficially, there has been a long standing rule of "no double dipping" damage. Meaning damage from one source per attack roll. This is why many compounds (toxins) start the damage either in the next IP, or the next combat turn.
And yes, this is an argument that has gone on for a long time (like, YEARS), and no, you won't find it in any books. But, your table is free to change it (as I know several tables have, for better or worse) if you choose to.
But cbsmith is correct, its a touch attack, or a defense attack (you are attacked with a melee attack/touch attack). Which has the advantages of +2 dice and considered a success on a tie.