Central nervous system effects of antihistamines on evoked potentials.

Sedation is the most common side effect of antihistamine therapy. As with many behavioral constructs, attempts at quantification are difficult, and consequently, subjective reports of antihistamine sedation are frequently relied upon. Evoked potential activity is one method to quantitate the brain's response to subtle cognitive change. Evoked potentials are characteristic shifts in the brain's electrical activity that are obtained by time-locking the ongoing EEG to a stimulus over repeated trials. A late positive component of the evoked potential (P3) has been related to various psychologic properties including expectation, selective attention, and information processing speed. Because of this relationship, we employed the latency of the P3 evoked potential to measure the cognitive effects of chlorpheniramine and terfenadine. In healthy young subjects, we observed that terfenadine produces significantly less cognitive slowing of the P3 potential than chlorpheniramine. This finding supports the subjective findings of reduced sedative side effects of terfenadine.