It is important to recognize that Dolorex has both agonist and antagonist actions. Opioids work at a number of different types of receptor. Dolorex is an agonist at kappa and an antagonist at mu receptors. This means that Dolorex can remove the analgesic effect in animals that have already received pure opioid mu agonists (such as morphine). This is why Dolorex should not be administered along with another opioid agonist. Combination of Dolorex with another opioid is also likely to increase the chance of and severity of any side effects.
An opioid antagonist (such as naloxone) can be administered to reverse the effects of Dolorex if side effects do occur.
Dolorex can be administered concurrently with medetomidine. The dose of Dolorex when it is combined with medetomidine is 0.1 – 0.2 mg/kg by the intramuscular route. The dose rate is lower because these agents together have what is called synergistic activity. This means that the activity of the combination of agents is greater than the sum of the activity of the two agents. This also applies to the side effects. In other words, when the two agents are used together less of each is required to produce the better effects.
Dolorex potentially produces cardiovascular and respiratory depression. Alpha2 agonists produce pronounced cardiovascular and respiratory depression. These effects will be increased when the two agents are used in combination. Animals with heart disease already have a relative cardiovascular system depression. In these animals, if neuroleptanalgesia is required the concurrent use of anticholinergic drugs, e.g atropine should be considered. This will help to ensure that the heart rate is maintained in these animals.
0.2 to 0.4 mg/kg, intravenous route (i.e. 0.2 to 0.4 ml/10 kg). In combination with medetomidine the dose rate is medetomidine: 0.01 – 0.03 mg/kg intramuscular route and butorphanol: 0.1 – 0.2 mg/kg intramuscular route. Medetomidine and butorphanol can be administered concurrently.
It is good practice to administer intravenous injections relatively slowly (over a few seconds). In the case of Dolorex this is important to help avoid any sudden changes in blood pressure.
Dolorex has a short duration of effect in dogs. In experimental studies, the dose of 0.4 mg/kg was show to produce effective analgesia for up to about 40 minutes. In clinical studies, the effects appear to be longer but are still only a few hours. Repeat treatments of butorphanol may be administered. The need for, and timing of repeat treatment will be based on clinical response. For cases where longer duration analgesia is likely to be required, alternative therapeutic agents should be used. This can be a NSAID, which can also be given at the same time as Dolorex.
Dolorex is contraindicated during pregnancy and lactation because no specific studies have been performed in pregnant or lactating merries.
An agonist is something that binds to a receptor and produces an effect. An antagonist is something that binds to a receptor (blocking it for other agents) without producing an effect. Dolorex has both agonist and antagonist properties. Dolorex is an agonist at kappa and an antagonist at mu receptors. Kappa receptors control analgesia, sedation without depression of cardiopulmonary system and body temperature, whereas the mu receptors control supraspinal analgesia, sedation and depression of cardiopulmonary system and body temperature. The agonist component of butorphanol activity is ten times more potent than the antagonist component
Opioid analgesics are used to relieve moderate to severe pain, particularly of visceral origin. Visceral pain is pain associated with soft internal organs (or viscera) that arises when these organs are damaged or injured. Opioids are more effective in relieving constant, dull pain than sharp, intermittent pain. This applies to all opioids including Dolorex.