Comparative and Veterinary Pharmacology

exerts effects on both the alpha 2A and alpha 2B subtypes, as well as having some
alpha 1 agonist activity. It is widely used in ruminants and the spinal effects of these
agents seems to be marked (Nolan et al.1987b), which is probably related to
high receptor density in spinal nociceptive pathways (Brandt and Livingston 1990 ).
Consequently, these drugs are more potent in ruminants than other species.
The alpha 2 agonist agent used most often in horses is detomidine (Jochle and
Hamm 1986 ). In this species it is effective as both an analgesic and as a sedative.
Medetomidine is licenced for use in dogs and cats and has a similar action (Table 8 ).
These drugs have been administered by intrathecal and epidural routes, as well as
intramuscularly and intravenously. There are reports of their synergistic interac-
tions with opioids, presumably at the spinal sites of action (Kalso et al. 1991 ). The
main side-effects of alpha 2 agonists are on the cardiovascular system, with
complex effects on both heart rate and blood pressure (Virtainen and McDonald
1985 ). Profound hypoxia associated with their use has been reported in ruminants,
particularly sheep (Nolan et al. 1986 ).
As with the opioids, specific, reversing agents are available to terminate the
effects of alpha 2 agonists in animals, such as atipamezole, used to reverse the
effects of medetomidine. These drugs are regarded as very useful adjuncts in
clinical practise.

Table 7Doses and intervals for NSAIDs in small mammals, birds and reptiles

Drug Mouse Rat Birds Reptiles

Acetylsalicylic acid (oral)

24 h

120 100 – –

Carprofen

24 h

5 5 1 2–4

Flunixin

24 h

2.5 2.5 3 0.1–0.5

Ketoprofen

24 h

• 5 2–5 2

Meloxicam

24 h

5 1 0.1 0.1–0.2

All doses are given in mg/kg for subcutaneous and intravenous injection except

where oral administration is indicated. Data from Dobromylskyj et al., ( 2000 );

Machin ( 2005 ); Mosley ( 2005 )

Table 8Doses of alpha 2 adrenergic agonists in animals

Species Detomidine Xylazine Medetomidine Romifidine

Horse 10–80 600–3,000 – 40–120

Cattle – 50–300 – –

Sheep – 50–100 – –

Dogs – 1,000–3,000 10–80 –

Cats – 1,000–3,000 50–150 –

Deer 60–90 500–1,000 – –

All doses are inmg/kg. Data from Bishop ( 1998 )

Pain and Analgesia in Domestic Animals 181