to describe with prospective methodology the therapeutic response to clonazepam in the respiratory panic disorder (PD) subtype versus the non-respiratory subtype in a long-term follow-up.

A total of 67 PD outpatients (DSM-IV) were previously divided into respiratory (n=35) and non-respiratory (n=32) subtypes and then openly treated with clonazepam for 8 weeks. Those who responded were then treated for 3 years. Demographic and clinical features were compared in the two groups. The instruments used to evaluate response were the Clinical Global Impression, the Sheehan Panic and Anticipatory Anxiety Scale, and the Panic Disorder Severity Scale.

In the first 8 weeks of treatment (acute phase), the respiratory subtype had a significantly faster response on all the major scales. During the follow-up and at the end of the study (week 156), there was no difference in the scale scores, and the reduction in panic attacks from baseline to end-point did not differ significantly between the two groups. After the acute phase treatment, the patients could undergo psychotherapy. In the respiratory subtype, the disorder had a later onset, was associated with a high familial history of anxiety disorder. The non-respiratory subtype had significantly more previous depressive episodes. Clonazepam had a safe adverse event profile during both phases of treatment.

The respiratory PD subtype had a faster response to treatment with clonazepam at 8 weeks than did the non-respiratory subtype and an equivalent response after 6 months of treatment. The response of clonazepam is clearly maintained during the long-term follow-up.