Contributors: John Dodam, Jo Murrell

 Species: Feline   |   Classification: Miscellaneous

Introduction

Indications for sedation

  • To reduce stress and anxiety.
  • Improve animal welfare.
  • Reduce risk of catecholamine-induced dysrhythmias Heart: dysrhythmia.
  • Reduce risk of handling difficult cats.
  • To enable a thorough clinical examination.
  • To perform diagnostic procedures.
  • To perform minor surgical procedures.
  • As premedication prior to general anesthesia General anesthesia: overview.

General rules

  • Allow adequate time for onset of action of the sedative after administration.
  • During this time it is very important to keep the cat in a quiet environment to get maximum sedative effect.
    Always monitor a cat that has been sedated.
  • IV administration generally produces the greatest sedative effect in the shortest time.
  • The time to peak sedation is longer after IM or SC administration, but the effect generally lasts longer.
  • Depressive effects on the CNS may be additive or synergistic with other agents.
  • Cats are particularly sensitive to hypothermia Hypothermia when sedated.
  • Weigh animal on scales - do not guess weight.
  • Combining sedatives often enhances potency while minimizing side effects.

Sedative agents

  • These include:
    • Acepromazine.
    • Benzodiazepines.
    • Opioids.
    • Alpha-2 agonists.
    • Ketamine.

Acepromazine

  • Acepromazine Acepromazine maleate is an antagonist at dopamine excitatory receptors.
  • Anti-emetic.
  • Increases epileptiform activity on EEG   →   lowers seizure threshold.
  • Reduces the sensitivity of the myocardium to circulating catecholamines, thereby reducing the risk of dysrhythmias Heart: dysrhythmia.
  • Some antihistamine activity.
  • Metabolized in the liver.

Side-effects

  • Prevents thermoregulation by depressing the hypothalamus thermoregulatory center. Cats are particularly susceptible to hypothermia while under acepromazine sedation.
  • Cardiovascular effects are dose dependant:
  • Causes hypotension by alpha-adrenoceptor blockade and vasodilation.
  • Overdose results in a rapid, weak pulse and collapse.
  • Minimal respiratory effects.
  • Can cause penile prolapse due to a sympatholytic action causing paralysis of the retractor penis muscle.
  • Causes PCV Hematology: packed cell volume to decrease:
    • Increased storage of RBCs in spleen.
    • Reduced hydrostatic pressure in arterioles increases movement of interstitial fluid into vessels.

Uses

  • Available in solution for injection (2 mg/ml and10 mg/ml) and tablet form. In US, available as 10 mg/ml solution.
  • Unpredictable effect following oral administration.
  • Dose is <0.1 mg/kg IM.
    Increasing the dose does not produce a proportional increase in sedation.
  • Allow at least 20 minutes to take effect after IM administration.
  • Duration of action is long - still some effect after 6 hours.
  • Consistency of sedative effects improved by combining acepromazine with an opioid.
  • Suitable premedication dose is 0.05 mg/kg for young, healthy cats.
  • Reduce the dose for the following:
    • Old cats.
    • Kittens.
    • Use at a very low dose or avoid in cats that are hypovolemic or hypotensive.
  • There is no scientific evidence to suggest that acepromazine alters seizure threshold.
  • In case of overdose and collapse:
    • Keep airway clear.
    • Administer IV fluids.
    • Maintain normal body temperature.
    • Alpha 1-adrenoceptor agonists may improve blood pressure if condition is serious.

Benzodiazepines

  • This drug group includes diazepam Diazepam and midazolam Midazolam.
  • CNS depression occurs due to facilitation of binding of the inhibitory neurotransmitter GABA to its receptor.
  • They reduce anxiety.
  • Good muscle relaxation.
  • No analgesic effects.
  • Degree of sedation depends on species and individual.
  • Healthy cats do not become sedated with a benzodiazepine used alone.
  • Excitement or aggression may be seen due to release of inhibited behavior patterns.
  • Very wide safety margin.
  • Metabolized in the liver.
  • Causes retrograde amnesia in humans.

Side-effects

  • Minimal cardiovascular or respiratory effects.
  • Synergism of respiratory depressive effects if combined with other CNS depressants.

Uses

  • Dose of diazepam or midazolam = 0.2 mg/kg by IV or IM injection.
  • Diazepam is insoluble in water and so is supplied as a clear solution in propylene glycol or as a white soya-bean emulsion.
  • Propylene glycol is painful to inject and may cause hypotension if injected rapidly intravenously.
  • Midazolam is water soluble.
  • Useful sedatives in young kittens, old cats and debilitated cats that may not tolerate acepromazine, especially if combined with an opioid.
  • Indicated as part of the premedication for animals undergoing contrast myelography as have an inhibitory effect on seizure activity.

Opioids

  • Opioids Analgesia: opioid produce sedation if used in cats that are debilitated, old or very young.
  • Do not produce sedation if used alone in healthy cats.
  • Synergism with other sedatives generally produces good sedation in healthy cats.

Side-effects

  • Minimal cardiovascular effects at clinical doses.
    Potent opioids may cause bradycardia.
  • Minimal respiratory effects at clinical doses. Significant respiratory depression only seen at very high doses.
  • Excitement generally seen only after high doses of opioids in healthy, pain-free cats.
  • Some opioids may cause vomiting.

Uses

  • Morphine Morphine:
    • Dose 0.1-0.2 mg/kg.
    • Vomiting common shortly after administration.
    • Use in combination with acepromazine for synergism of sedative effect
  • Buprenorphine Buprenorphine:
    • Dose 0.02-0.03 mg/kg.
    • Very unlikely to cause vomiting.
    • Slow onset of action - give at least 30 min before sedation required.
    • Long duration of action. Acepromazine and buprenorphine combination produces useful sedation for up to 4 hours
  • Omnopon:
    • Dose 0.4 mg/kg.
    • Produces profound sedation when used in combination with acepromazine.
    • Useful sedation for aggressive dogs
  • Meperidine Pethidine:
    • Dose 2-5 mg/kg.
    • Short duration of action: <2 hours.
    • Can be used alone in debilitated animals, or in combination with acepromazine in healthy cats.

Alpha-2 agonists

  • Dexmedetomidine Dexmedetomidine, Medetomidine Medetomidine and xylazine Xylazine.
  • Can produce profound sedation.
  • Reversible with atipamezole Atipamezole.
  • Provide good analgesia.
  • Inhibit anti-diuretic hormone release   →   increase urine production.
  • Increase blood glucose concentration.
  • Decrease gut motility.
  • Have an ecbolic effect on the uterus (xylazine).
  • Inhibit body temperature regulation.
  • Frequently cause vomiting.
  • Stings on IM administration.

Side-effects

  • Cardiovascular effects:
    • Profound bradycardia Heart: dysrhythmia and second degree heart block may occur. Caused by central stimulation of parasympathetic nervous system.
    • Initial hypertension Hypertension caused by stimulation of post-synaptic receptors in peripheral vessel walls results in poor tissue perfusion.
    • The brief initial hypertension is followed by prolonged hypotension, caused by CNS depression.
    • Coronary circulation is reduced.
    • May sensitize the heart to catecholamine induced dysrhythmias Heart: dysrhythmia 
  • Respiratory effects:
    • Respiratory rate decreases and arterial oxygen tension tends to decrease.
    • Cyanosis is common, possibly due to increased oxygen extraction and venous desaturation rather than decreased arterial oxygen tension.

Uses

  • Alpha-2 agonists are very convenient drugs, producing profound sedation rapidly, which is equally as rapidly reversible.
    Side-effects can be very serious. Even though the animal survives, its organ functions may be permanently impaired.
  • Dexmedetomidine and medetomidine has less interaction with receptors other than alpha-2 adrenoceptors than xylazine. Dexmedetomidine is the active isomer contained within medetomidine and is therfore most specific for the alpha 2 receptor. 
  • Sedation (Dose: 0.01-0.08 mg/kg) achieved with medetomidine administered IM is inconsistent, probably due to poor absorption.
  • Side-effects increase with dose, therefore use the minimum dose possible.
  • Reduce the dose required by combining with any of the opioids Analgesia: opioid  →   eg dose can be reduced to 0.02 mg/kg medetomidine IM.
  • Provide supplemental oxygen with a face mask where possible.
    Alpha-2 agonists greatly reduce the dose required of any anesthetic agent used consequently. Also, they reduce cardiac output, so it takes longer for intravenous induction agents to produce loss of consciousness.Allow plenty of time before giving incremental doses of induction agents.
  • Atipamezole Atipamezole is a specific alpha-2 antagonist, which rapidly reverses the effects of medetomidine or dexmedetomidine. It reverses analgesia as well as sedative effects.
  • It is not recommended to administer atropine Atropine to counteract the bradycardic effects of alpha-2 agonists. Atropine increases the heart rate, but also increases the hypertension and poor peripheral perfusion, increases the risk of dysrhythmias, increases cardiac work and oxygen consumption, and decreases ventricular filling time.
    Although cats may appear profoundly sedated, they can occasionally suddenly stir and bite in response to stimulation.
  • Medetomidine or dexmedetomidine are absorbed well through the oral mucosa, with a similar bioavailability to IM administration. Therefore sublingual administration can be used, with care not to overdose.