Marek's Potion of Antidote can be obtained only from Marek himself in Baldur's Gate Chapter 5. It is the end goal of the quest Marek and Lothander and is needed to cure the party of a deadly poison. It can be used up to ten times and must be used by each party member individually.
|“||Marek's potion looks to have 10 doses. More powerful than a normal potion of antidote, this potion would neutralize even the most lethal of poisons.||”|