Arcane Consumption

 
Prerequisite(s): Arcane Toughness, Toughness, Arcane Caster level 6+
 
Benefit: Once per day as a swift action, you can grant the next spell you cast a +4 bonus on its save DC. You must cast and complete this spell on the same turn that you use a swift action to activate this feat. In return, you take a -4 penalty to Constitution for 12 hours and are fatigued.
 
Source:PHB II