The complexity of pain perception and response to pain requires a multimodal analgesia treatment, which typically relies on a combination of nonsteroidal anti-inflammatory drugs, local anesthetics, N-methyl-D-aspartic acid antagonists, A2-adrenoceptor agonists, and opioids.1 Opioids are one of the most efficient analgesics. They activate 1 or more subclasses of specific opioid receptors in accordance with the affinity or intrinsic activity of each drug.2 However, the use of opioids is limited in horses because they may cause excitement and increased locomotor activity. These undesirable effects are especially evident after administration of a pure opioid agonist.3–6
Buprenorphine is a highly lipophilic semisynthetic partial OP3 (μ) opioid receptor agonist. It may also be defined as an agonist-antagonist opioid because it is a κ receptor antagonist in several species.7 Buprenorphine has a unique pharmacokinetic pattern, with a high affinity for receptor binding and prolonged effects. It may be an alternative to use of classic opioid receptor agonists for the treatment of horses with acute and chronic pain because it apparently causes less intense adverse effects, especially with regard to the CNS.8 The high analgesic potency of buprenorphine (25 to 50 times as high as the analgesic potency for morphine), prolonged effects, and low cost have contributed to the widespread use of buprenorphine in laboratory and small domestic animals.9–11
To our knowledge, only 3 studies12–14 have reported the effects of buprenorphine in horses. In one study12 in which investigators assessed the cardiopulmonary changes induced by buprenorphine in healthy horses and horses with chronic obstructive pulmonary disease, excitement and sympathetic cardiovascular stimulation were observed, with no changes in blood gas variables. In another study,13 the combination of buprenorphine and detomidine did not induce hormonal, metabolic, or physiologic changes, including heart and respiratory rates, pH, PaO2, and PaCO2. In our preliminary study14 in the same horses used in the study reported here, we verified that cardiopulmonary and digestive tract alterations were induced by buprenorphine, which revealed excitement and hemodynamic stimulation, minimal changes in arterial blood gas tensions, and a decrease in gastrointestinal motility.
The objective of the study reported here was to investigate whether SLA was possibly related to stimulation of the CNS that resulted from the administration of buprenorphine. We also evaluated the timing and intensity of antinociceptive effects induced by various doses of buprenorphine in horses.
Spontaneous locomotor activity
Hoof-withdrawal reflex latency
Skin-twitching reflex latency
Temgesic, Schering-Plough, Rio de Janeiro, Brazil.
Tec Horse 12, Purina, São Paulo, Brazil.
LAT-2, Banner Engineering Corp, Minneapolis, Minn.
CR200 datalogger, Campbell Scientific Inc, Logan, Utah.
FLEX Series 7990, Veeder-Root, Simsbury, Conn.
GraphPad Prism, GraphPad Software Inc, San Diego, Calif.
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