The effect of long-term imipramine treatment on carbon dioxide-induced anxiety in panic disorder patients.

The authors examined whether long-term treatment with imipramine would decrease CO2-induced anxiety in 10 patients with panic disorder. The patients underwent CO2 testing after single-blind placebo testing and again after imipramine treatment. Scores on self-rated visual analog mood scales and panic attack symptom scales showed that the anxiogenic effects of CO2 were significantly reduced during long-term imipramine treatment. These results suggest that the mechanisms underlying CO2-induced anxiety may be similar to those involved in the pathophysiology of panic disorder.