CARDIOPULMONARY EFFECTS OF MEDETOMIDINE IN HEARTWORM-INFECTED AND NONINFECTED DOGS

Medetomidine, an investigational drug indicated for clinical use as a short-term chemical restraint in dogs, was evaluated for its cardiopul monary effects, in 10 naturally heartworm-infected (HW+) and 10 noninf ected (HW-) Beagles. The drug was randomly administered Iv (30 mu g/kg of body weight) and IM (40 mu g/kg) in single injections to all dogs. Heart rate, respiratory rate, ECG, blood gas tensions, blood pH centr al venous and arterial pressures were measured at 0, 15, 30, 60, 90, 1 20, and 180 minutes. Medetomidine induced an immediate significant (P less than or equal to 0.001) increase in mean arterial blood pressure followed by decreased blood pressure that remained below normal throug hout the study in both groups, irrespective of route of administration . Medetomidine increased central venous pressure, over time, for both groups and both routes of administration. Heart and respiratory rates were significantly (P less than or equal to 0.001) decreased after med etomidine administration and remained reduced for the duration of the study in all dogs. The ECG variables were not significantly different between groups or between routes of administration. The HW+ dogs tende d to have higher mean Pa-O2 than did HW- dogs at several postinjection determination times, particularly when the drug was administered IM. The Pa-O2 decreased during the first 30 minutes in both groups and ten ded to increase gradually thereafter. The pH decreased over time for b oth groups and both routes. A significant (P less than or equal to 0.0 5) decrease in pH was seen in the HW- dogs, compared with HW+ dogs at each measuring time for both routes. The Pace, did not significantly c hange for groups or routes. In general, bradycardia was the predominan t cardiovascular effect seen after medetomidine administration in all dogs, irrespective of route. Lowering of blood pressure and heart rate (after a transient blood pressure increase) was synchronized with sed ation in these dogs. The overall clinical response with regard to card iopulmonary effects in HW+ dogs was similar to that in HW- dogs.