THE EFFECT OF ACETAZOLAMIDE ON VENTILATION IN PANIC DISORDER PATIENTS

Objective: Patients with panic disorder are behaviorally hypersensitiv e to CO2 inhalation and may also be biologically hypersensitive. A rep ort by Mathew et al. showed, however, that administration of the carbo nic anhydrase inhibitor acetazolamide, which is believed to increase b rain CO2 level, did not cause panic in panic disorder patients. The au thors of the present study noted that respiratory frequency did not in crease in the earlier experiment and wondered whether respiratory stim ulation occurred during acetazolamide administration, as would be expe cted if CO2 level increases significantly. Method: Ten patients with p anic disorder and six normal control subjects received injections of a cetazolamide, 1 g i.v., as per the Mathew et al. protocol, during brea th by breath measurement of both tidal volume and frequency of respira tion. Results: Three patients had panic attacks, one before receiving acetazolamide, one during the injection, and one 2 minutes after injec tion. Only the last of these attacks appeared possibly attributable to acetazolamide. None of the control subjects panicked. Neither patient s nor control subjects exhibited meaningful change in tidal volume, re spiratory frequency, or minute ventilation, and both groups experience d a trend toward significant decrease in overall levels of anxiety and dyspnea after acetazolamide injection. Conclusions: The authors repli cated the earlier finding that acetazolamide is not panicogenic in pat ients with panic disorder but also showed that at the dose given, ther e is no meaningful effect on ventilation. If acetazolamide does affect CO2 levels it does so in a way that does not stimulate ventilation. T herefore, the acetazolamide injection results of Mathew et al. and of the present study do not challenge hypotheses linking panic attacks to hypersensitive respiratory control mechanisms.