Tranquilization decreases anxiety and induces a sense of tranquility without drowsiness. Drug-induced sedation has a more profound effect and produces drowsiness and hypnosis. Analgesia is the decrease of pain.
Many drugs cannot be categorized by only one pharmacological effect (ie, as only tranquilizers, only sedatives, or only analgesics). Although many psychotropic drugs can either tranquilize or sedate, depending on the dose administered, many sedatives are also analgesics.
Drugs classified as tranquilizers, sedatives, or analgesics can also have other effects (eg, behavior modification, prevention of nausea/vomiting). Drugs that have some of these effects but are used mainly for other properties (eg, as antispasmodics, antiemetics, or preanesthetics) are not discussed here.
Single-use doses are emphasized because many situations require only a brief duration of effect; however, frequency of administration is also provided for drugs likely to be used for multiple-dose treatment.
Schedule restrictions, extralabel use, or precautions in the use of these drugs may be applicable; the product label and referenced texts should be consulted for information on the pharmacology and alternative applications of each drug.
Analgesics are covered elsewhere (see Analgesics Used in Animals).
For a discussion of injectable benzodiazepines (diazepam and midazolam), see Anticonvulsants for Emergency Treatment of Seizures in Dogs and Cats.
For specific therapeutic recommendations, including dosages, refer to the relevant disease chapter.
Acepromazine as a Tranquilizer or Sedative for Animals
Acepromazine is a phenothiazine tranquilizer and sedative that works by inhibiting central dopaminergic receptors. It also has muscarinic action and blocks norepinephrine and adrenergic receptors. Because of its effect on alpha-2-receptors in vascular smooth muscles, acepromazine can cause vasodilation.
In horses, the half-life of acepromazine is 2.5 hours, and IV administration can appreciably increase blood flow through digital arteries and laminae.
In small animals, sedation can occur within 10 minutes and last 4–6 hours. Doses considerably lower than the labeled dosage are commonly used for small animals in clinical practice.
Acepromazine has been administered as a behavior-modifying agent in animals with anxiety; it is also used to treat horses with laminitis.
Sedation and ataxia are common adverse effects of acepromazine. Involuntary muscle movements, twitching, and dystonia can also occur. Disinhibition (exhibition of typically inhibited behavior, such as excitement or aggression), paradoxical excitation (excessive excitement, anxiety, or aggression) have been reported in dogs treated with acepromazine.
Because acepromazine can produce excessive vagal tone, caution is recommended in brachycephalic breeds, for which the effect can be particularly severe. Hypotension can also occur, so blood pressure should be monitored, and caution should be exerted if acepromazine is administered concomitantly with other hypotensive drugs.
Some older books described an increased risk of seizure associated with acepromazine in dogs with epilepsy; however, this effect was not confirmed in a retrospective study in animals prone to seizure that were administered acepromazine as an anesthetic adjunct (1).
Pearls & Pitfalls
|
In horses, persistent penile prolapse has been reported after the use of acepromazine and might depend on the dose, with higher doses being associated with increased risk.
A withdrawal time for acepromazine of at least 7 days for meat and 48 hours for milk was established in Canada (2). In the US, no withdrawal times have been established, and use in food-producing animals is considered extralabel.
Alfaxalone as a Tranquilizer or Sedative for Animals
Alfaxalone is a synthetic neuroactive steroid that interacts with gamma-aminobutyric acid (GABA) receptors in the CNS to produce anesthesia and muscle relaxation. It does not provide analgesia.
The half-life of alfaxalone is short in small animals (1 hour); higher doses, however, might be associated with a longer elimination time.
Alfaxalone is used as a general anesthetic that can be administered as a single IV bolus or as a CRI for maintenance anesthesia. IM administration is also possible; however, pain associated with the injection has been reported, as well as excitement, incoordination, and hyperreactivity upon recovery.
As an anesthetic agent, alfaxalone can cause CNS depression, result in respiratory depression, and potentially decrease blood pressure.
Alfaxalone has been used as an anesthesia induction agent in exotic species such as rabbits, ferrets, reptiles, and birds. No data have been published on the use of alfaxalone in large animal species.
Propofol as a Tranquilizer or Sedative for Animals
Propofol is a widely used short-acting anesthetic that produces CNS depression through its action on GABA receptors. It decreases GABA dissociation from its receptors, thereby increasing chloride ion conductance across the channels and hyperpolarizing neuronal postsynaptic membranes.
Propofol can produce a brief anesthesia with a rapid and smooth recovery. It can also be administered as a CRI for refractory status epilepticus (see Anticonvulsants for Emergency Treatment of Seizures in Dogs and Cats) and to maintain an anesthetized state for surgical procedures (notably for neurosurgeries).
Apnea and respiratory depression are the most common adverse effects of propofol and are dose dependent. Propofol can also cause vasodilation and subsequent hypotension. Spontaneous muscle movements (paddling, tremors, and muscle rigidity), panting, nystagmus, salivation, and retraction of the tongue have been observed in some animals and could be mistaken for seizures.
In horses, propofol can also cause excitement and myotonus. In cats, Heinz body formation and methemoglobinemia have been reported after repeated anesthesia episodes; however, the problem has not been consistent with routine propofol use.
References
Tobias KM, Marioni-Henry K, Wagner R. A retrospective study on the use of acepromazine maleate in dogs with seizures. J Am Anim Hosp Assoc. 2006;42(4):283-289. doi:10.5326/0420283
Haskell SR, Gehring R, Payne MA, et al. Update on FARAD food animal drug withholding recommendations. J Am Vet Med Assoc. 2003;223(9):1277-1278. doi:10.2460/javma.2003.223.1277
