Blood Pressure and Heart Rate Response of Panic Disorder Patients Receiving Imipramine in a Dose-Response Treatment Paradigm

This article reports the effects of imipramine on heart rate and blood pressure in panic disorder patients who participated in an 8-week double-blind dosage response treatment protocol. At the end of a placebo baseline, patients were randomly assigned to placebo or one of three weight-adjusted imipramine dosages: low (0.5 mg/kg per day), medium (1.5 mg/kg per day), or high (3.0 mg/kg per day). It was demonstrated that imipramine had no significant effect on sitting or standing diastolic or systolic blood pressure. Although there was a trend toward a systolic blood pressure drop with positional change, it did not reach statistical significance. There were no significant changes in diastolic blood pressure with postural change. Imipramine did increase sitting and standing heart rate without revealing a clear dosage correlation. In contrast to the pretreated state, the reflex heart rate response to postural change was significantly increased in the posttreatment state, also in a dosage-independent manner. Within the high-dose imipramine group, the baseline sitting to standing heart rate increase was significantly higher in those who dropped out because of drug side effects compared with those who remained. Evidence from this study suggests that imipramine has a dosage-independent effect on resting and reflex heart rate. Future studies should consider postural heart rate reactivity as a potential measure of intolerance to the side effects of high doses of imipramine.