MORPHINE ● Full µ agonist. ● Excellent analgesic. ● Last 2 to 3 hours in dogs and 4 to 6 hours in cats. ● Commonly used in combination with acepromazine or alpha 2 agonists. ● Usually causes nausea and vomiting. ● Histamine release may occur after rapid IV injection. METHADONE ● Full µ agonist. ● Causes effects very similar to morphine but less sedation and a longer duration of action. ● Less likely to cause vomiting or excitement. ● Can be given IV without causing a histamine release. ● Has additional analgesic properties. HYDROMORPHONE ● Full µ agonist. ● Remarkably similar to morphine but more potent with a longer duration of action. ● Unlikely to cause a histamine release. FENTANYL ● Full µ agonist. ● Very potent analgesic. ● Very quick onset of action. Usually within 2 to 3 minutes after IV administration and lasts about 20 minutes. ● Usually given as a constant rate infusion (CRI) due to short action. ● Causes bradycardia and respiratory depression. Use of opioids in cats Opioids can be used safely in cats to provide highly effective analgesia. Due to the deficiency in the hepatic glucuronyl Summary In this chapter, we discussed the many different options for pre- medications, as well as any reversal agents that are available. You should have a good understanding of these drugs.
● Does not cause vomiting or histamine release. ● Fentanyl transdermal patches can be used to provide analgesia for up to 72 hours in dogs and cats. BUPRENORPHINE ● Partial agonist at the µ receptor and reaches a ceiling effect that cannot be passed by an increase in dosage. ● Agonist at the κ receptors. ● Slow onset of action regardless of the route of administration – usually takes about 30 minutes to reach its full effect. ● Long duration: 6 to 8 hours in dogs and even longer in cats ● Very well absorbed across the oral mucosal membranes. This is commonly used in cats. This is a great choice for transmucosal opioid medication in cats that need postoperative pain control. ● Does not cause vomiting or excitement. BUTORPHANOL ● Antagonist at the µ receptor and agonist at the κ receptor. ● NOT recommended for the first line of analgesia in patients with moderate to severe pain. ● Great sedative and commonly used with acepromazine or alpha 2 agonists for no painful procedures. ● Does not cause vomiting or excitement. OPIOID ANTAGONIST These two drugs can be used to reverse the effect of opioids or to treat an opioid overdose. They are: ● Naloxone : most commonly and widely available reversal ● Naltrexone : not commonly used but is available.
transferase enzyme system in cats, opioid metabolized by glucuronidation will have a longer half-life in cats than in dogs.
INJECTABLE ANESTHETICS USED AS INDUCTION AGENTS
Learning objectives Discuss many of the commonly used injectable anesthetics drugs. Explain the effect that the drug will cause the patient. Predict any side effects that you may see when using a certain drug. Identify the pros and cons of using total intravenous anesthesia. In the previous chapter, we discussed drugs used as pre- medication in preparation for the induction of general anesthesia. The pre-medications cannot be used to induce a Why induce anesthesia with injectable agents? The use of injectable drugs to induce general anesthesia has some advantages over the use of inhalational agents. With inhalational agents: ● A special machine is needed to deliver anesthetic gas. ● Anesthesia ensures more slowly and may unmask excitement stages. ● Restraint of the patient may pose some risk to the veterinary staff. ● Anesthetic gas can contaminate the environment. ● Some inhalational anesthetic commonly used are irritants to the airway and cause patients to hold their breath. Therapeutic index The therapeutic index is the ratio of the amount of a drug that causes death to the amount that causes a therapeutic effect. The higher the therapeutic index, the safer the drug.
state of CNS depression to cause general anesthesia. The state of CNS depression consistent with general anesthesia can be induced by these specific injectable drugs. Most Commonly Used Injectable Anesthetics in Small Animal Medicine ● Barbiturates: Pentobarbital (used for euthanasia). ● Phenolic compounds: Propofol. ● Steroids: Alfaxalone. ● Imidazole derivatives: Etomidate. ● Cyclohexanones: Ketamine and Tiletamine. PROPOFOL Propofol is a very commonly used induction agent used today because of the rapid awakening and non-cumulative effect. Propofol comes in a formulation that lasts 28 days after being opened. This drug is rapidly metabolized by the liver by glucuronidation to an inactive compound that is excreted by the kidneys. ● Rapid onset of 60 to 90 seconds and short duration of action of about 10 minutes. ● Decreases intracranial pressure. ● Some animals can develop muscle rigidity and front limb paddling or other excitatory movements after induction. This is called the propofol shakes . ● Propofol does NOT raise the seizure threshold. It is very commonly used as an effective anti-convulsant agent and administered to dogs with refractory epilepsy as a CRI.
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Book Code: VFL1524
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