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Abstract

The sedative and analgesic effects of medetomidine were evaluated in heartworm-infected (HW+) and uninfected (HW-) beagle dogs by intravenous (IV) and intramuscular (IM) administration of 30 micrograms/kg and 40 micrograms/kg doses, respectively. Posture, response to noise and the pedal reflex were monitored. A procedure for mock radiographic positioning was performed to evaluate its overall clinical use. Observation times were 0, 15, 30, 60, 90, 120 and 180 min. In addition, the times from injection until the dog could not stand on its feet (down time), from lateral to sternal recumbency (sternal recumbency time), and from sternal recumbency to rising again (rising time) were also noted. Medetomidine produced rapid sedation and analgesia by both routes. Down times for the IM and IV routes were similar, which verified the manufacturer's recommended doses. The HW+ dogs had shorter down times, probably owing to increased blood flow to the brain caused by adrenergic alpha-2 activity. Sternal recumbency and rising times did not differ between the groups, suggesting a similar metabolism. Sedation and analgesia were adequate for performing the procedure in all dogs. HW- dogs showed less resistance to handling during the procedure than HW+ dogs. Overall, medetomidine seems to be a suitable agent for short-term chemical restraint in dogs, even with subclinical heartworm infestation.

Clinical comparison of medetomidine with xylazine/l‐methadone in dogs

“…The acute and long lasting decrease in respiratory rate after treatment with medetomidine was also observed by Clarke and England (1989), England and Clarke (1989a, b) and Räihä and others (1989a, b), and was not dose related, although Young and others (1990) did report a dose‐related decrease. The intermittent dyspnoea, interspersed with apnoea, was also recorded by Clarke and England (1989) and the observation of unchanged blood gas values agrees with observations by Pettifer and Dyson (1993) and Venugopalan and others (1994). In contrast there were adverse effects on respiration and the blood acid/base status after treatment with xylazine plus 1‐methadone, which in half the dogs caused severe panting.…”

“…These observations are in general in agreement with α 2 ‐effects on cardiovascular function as described by Clarke and England (1989), Lombard and others (1989) and Vainio (1989). Experimental and clinical studies using doses calculated on the basis of body surface area have shown that these substance‐specific cardiovascular responses, even in dogs with severe (heartworm‐related) cardiac insufficiency did not result in life‐threatening problems (Venugopalan and others 1994, C. L. Tyner, B. J. Woody, J. S. Reid, E. P. Chafetz, H. A. Lederer, F. F. Norton, W. Jöchle, unpublished observations). Studies in dogs with instruments implanted in their hearts have shown that these typical α 2 ‐adrenergic effects are fully established with an intravenous dose of 10 μg/kg medetomidine, reach a maximum with a dose of 30 μg/kg, and are prolonged with higher doses (D. Franklin, personal communication).…”