Respiratory depression of intravenous hydroxyzine in man: potency, duration, and lack of reversal by naloxone.

The effects of intravenous hydroxyzine and hydroxyzine with naloxone on respiration were determined in man. Drug effect was expressed as the shift in the 20-L intercept of the respiratory response curve measured by a rebreathing technique. The time-effect curve of hydroxyzine was found to be the same for hydroxyzine alone and in combination with naloxone, but significantly different from placebo or naloxone alone. The duration of respiratory depression in man resulting from hydroxyzine, 100 mg IV, is greater than 3 hours. Our data did not support the hypothesis that the respiratory depressant and recently discovered antinociceptive effects of hydroxyzine result from endorphin release or are mediated by opiate receptors.