Romifidine (
STH 2130-Cl or
Sedivet) is an alpha 2-agonistic imino-imidazol
sedative for intravenous use in horses recently developed by Boehringer Ingelheim, Vetmedica GmbH. An exploratory study was done in nine warm-blood horses, randomly divided into three groups, which received different dosages of
romifidine (0.04, 0.08 and 0.12 mg/kg of
body weight (BWT) intravenously (i.v.)) with at least one week's interval between tests.
Romifidine induced a marked
bradycardia accompanied by second degree atrioventricular (
AV) block and some sinus blocks at all tested dosages. A placebo (NaCl 0.9% i.v.) given 5 min before and after
romifidine did not affect the cardiac disturbances induced by
romifidine. A low dose of
atropine sulphate (0.005 mg/kg of BWT i.v.) given 5 min before
romifidine counteracted the
bradycardia and caused a normal to increased heart rhythm at all
romifidine dosages. A higher dose of
atropine sulphate (0.01 mg/kg of BWT i.v.) administered 5 min before sedation induced a
tachycardia (average 70 beats/min) at all
romifidine dosages and completely prevented the
bradycardia and the
heart blocks. The positive chronotrope effects of
atropine sulphate were attenuated by increasing doses of
romifidine. The effects of
atropine sulphate (low or high doses) given 5 min after
romifidine only appeared after 5 min. Both dosages counteracted the
bradycardia and suppressed the
heart blocks. No
atropine-dependent side effects were observed in non-fasted horses. The degree of the
romifidine induced sedation was not affected by the use of
atropine sulphate given before or after
romifidine.