Circulatory pattern and duration of action of naloxone in dogs with and without opioid pretreatment.

We investigated the circulatory pattern of naloxone reversal after high-dose fentanyl infusion in dogs. Within 1 min there was a sudden decrease in total peripheral resistance with a concomitant increase in stroke volume index. All other parameters changed back in direction of pre-fentanyl values in various degrees with peak effects in about 3-7 min. The persistency of reversal was different for individual parameters, but 20 min after injection of naloxone almost all changes induced by antagonisation of narcotic activity had returned to pre naloxone levels. In a control series with animals not pretreated with opioid, naloxone was shown to have no specific pharmacologic action of its own.