Potion of Fire Breath transform the throat so that is possible to shoot a firebreath towards the target in an arc. It can be bought from the Sorcerous Sundries in Baldur's Gate. In Baldur's Gate II it is sold by Ribald Barterman, Roger in the Athkatla Temple sewers and by the potion merchant in Ust Natha.
By drinking the potion of firebreath, it magically transform the throat so that it is capable of a giant breath of fire spewing forth in an arc. The effect does 6D10 damage to the target with a save vs. breath weapon for half.