Carbon dioxide test as an additional clinical measure of treatment response in panic disorder.

OBJECTIVE We aim to determine if a treatment with a dose of clonazepam--2 mg/day, for 6 weeks, blocks spontaneous panic attacks and the ones induced by the inhalation of 35% carbon dioxide (CO2) in panic disorder (PD) patients. The CO2 challenge-test may be a useful addition tool for measuring the pharmacological response during the initial phase (6 weeks) in the treatment of PD. METHOD Eighteen PD patients drug free for a week participated in a carbon dioxide challenge test. Fourteen had a panic attack and were openly treated for a 6-week period with clonazepam. At the end of the 6-week period they were submitted again to the CO2 challenge test. RESULTS After 6 weeks of treatment with clonazepam, 12 of 14 PD patients (85.7%) did not have a panic attack after the CO2 challenge test. Just 2 of 14 patients (14.3%) had a panic attack after the CO2 challenge test. Ten of 14 (71.4%) PD patients had panic free status after clonazepam treatment. The 2 patients who had a panic attack in the sixth week, after the CO2 test, did not have panic free status after the treatment with clonazepam. CONCLUSION The CO2-test may be a valid tool for testing and predicting the drug response.