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Anaesthesia > Sedatives and Tranquilisers > Flashcards

Sedatives and Tranquilisers Flashcards

0
Q

What is the definition of an anxiolytic?

A

An agent that reduces anxiety without causing sedation.

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1
Q

What is the definition of a tranquilliser?

A

An agent that affects mood.

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2
Q

What is the definition of a sedative?

A

An agent that causes drowsiness

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3
Q

What is the definition of a hypnotic?

A

An agent that depresses the CNS and induces sleep at higher doses.

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4
Q

What is the definition of a neuroleptic?

A

An agent that reduces aggression and agitation.

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5
Q

What are the four main groups of drug that act as sedatives and tranquillisers?

A

Phenothiazines
Butyrophenones
Benzodiazepines
Alpha2-agonists

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6
Q

What are the characteristics of Phenothiazines and how do they act on the CNS, gut, CVS and other areas?

A

CNS- they are antagonists for dopamine and are used as tranquillisers, sedatives and anxiolytics. They have anti-emetic properties but NO analgesic properties.
CVS- block a1 receptors= vasodilation and hypotension, antiarrythmic action.
GIT- antispasmodic action on the gut
MISC- antihistamine, antimuscarinic, seratonin block.

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7
Q

How is Acepromazine (ACP) presented and what is it used for?

A

it is a pale yellow crystalline solid prepared in liquid, gel and tablet form. It is used as an anxiolytic/tranquilliser/sedative and for pre-med to reduce the dose of other agents. It can help treat travel sickness in dogs and cats.

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8
Q

How is Acepromazine administered in dogs and cats?

A

Injected at 2mg/ml for IV or IM. Subcutaneous absorption is unpredictable.

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9
Q

How is acepromazine administered in large animals?

A

Injected at 10mg/ml for IV and IM. Licensed for horses not intended for human consumption- not in breeding stallions (prepuce-penis injury due to protrusion)

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10
Q

What is the dose of acepromazine in tablet and gel form?

A

tablet- 10mg or 25mg for dogs and cats

‘Sedalin’ gel for horse sedation 35mg/ml

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11
Q

What are the pharmacokinetics of acepromazine?

A

Oral bioavailability is variable (20-55%).
Duration is 4-6hrs
Onset- 20mins after IM and 5 mins after IV
metabolised in the liver and excreted in the urine
conjugated and non conjugated metabolites excreted in the urine
Parenteral dose range 0.025-0.1mg/kg. lower end if IV and combined with opioid.

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12
Q

What do different levels of dose of acepromazine cause?

A

Low levels affect behaviour, high levels cause sedation that is variable and unpredictable. Higher doses will not increase the sedation but will just prolong the level of sedation and increase the severity and occurrence of side effects.

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13
Q

What route of administration for Acepromazine is preferred and how should the other be done?

A

IM, if given IV it should be given slowly to avoid vasodilation and hypotension. Shocked and hypovolaemic animals require IV fluids and so very low doses are used here.

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14
Q

What relationship does acepromazine have with other drugs?

A

it potentiates them e.g. opioids, general anaesthetics-barbiturates and local anaesthetics.

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15
Q

How should Acepromazine be used in certain dog breeds and those predisposed to epilepsy?

A

Boxers (brachiocephalic and have congenital valvular stenosis) and giant breeds- used greatly reduced doses.
should be avoided as it lowers the threshold for epileptiform seizures.

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16
Q

What is the only phenothiazine that is a potent analgesic?

A

Methotrimeprazine- small animal immobilon.

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17
Q

What are 4 other phenothiazines other than ACP?

A

Propionylpromazine, chlorpromazine, promazine and promethazine- this is an irritant and should be given deep IM it has potent antihistamine activity.

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18
Q

What are Butyrophenones and what are their effects on the CNS and CVS?

A

they are used to modify behaviour more so than the phenothiazines. CNS- dopamine antagonists with a mild sedative action. They are potent antiemetics. CVS- vasodilation and hypotension.

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19
Q

What is Azaperone and what is it used for?

A

It is a butyrophenone that is sued to modify behaviour, it is licensed in pigs for treatment of aggression, transport stress, obstetric conditions and pre med for local and general anaesthetic.

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20
Q

What are the pharmacokinetics for azaperone?

A

Deep IM injection, leave undisturbed for 20mins, duration is 2-3hrs and it potentiates anaesthetic agents.

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21
Q

What are the pharmacological effects of azaperone?

A

there is dose related sedation in pigs and a slight fall in blood pressure.

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22
Q

What is fluanisone and what is it used for?

A

combined with fentanyl for neurolept analgesia in mice, rats, rabbits and guinea pigs.

23
Q

What is droperidol and what is it used for?

A

It is a potent neuroleptic agent with a duration of 6-8hrs. It is a potent anti-emetic and is used with fentanyl to provide neuroleptananalgesia.

24
Q

What is the mechanism by which benzodiazepines work?

A

via potentiation of GABA mediated inhibition- the primary neurotransmitter in the CNS.
GABA(A) is the receptor that gates a postsynaptic chloride channel. When GABA binds to GABA(A) the channel opens and chloride conduction is increased. This results in hyperpolarisation of the membrane which decreases the ability for an action potential to be conducted. The benzodiazepine binds to the receptor and enhances the action of GABA on Cl ion conductance so they make the membrane more hyperpolarised. If GABA is absent benzodiazepines have no efficacy.

25
Q

What effects do benzodiazepines have on the CNS, CVS/RESP system?

A

CNS- primarily anxiolytic action, muscle relaxation, anticonvulsant, little sedation.
CVS/RESP- little depression

26
Q

How do benzodiazepines interact with other drugs and how are they metabolised?

A

They have synergistic effects with other central depressants such as barbiturates and antihistamines. They are metabolised in the liver to active metabolites.

27
Q

What is an important characteristic of diazepam?

A

It is insoluble in water and so has to be dissolved in propylene glycol which can cause thrombophlebitis, pain on injection and cardiac arrhythmia.

28
Q

What are the pharmacokinetic aspects of diazepam?

A

Administer via IV or oral. It has a rapid onset and is metabolised in the liver but does not induce hepatic enzymes and so duration of action may be prolonged with severe hepatic dysfunction. Some of the metabolites may be active. Excreted in the urine.

29
Q

What are the pharmacological effects of diazepam?

A

It has variable sedation, muscle relaxant but can induce panic in horses, anticonvulsant and minimal depression on the CVS/RESP.

30
Q

What are the clinical uses of diazepam?

A

By IV to control status epilepticus, to stimulate appetite, alongside ketamine in horses and smallies to induce and maintain anaesthesia (in compromised animals) and with hypnorm in smallies to produce anaesthesia and muscle relaxation.

31
Q

What is Midazolam?

A

A water soluble benzodiazepine that does not cause thrombophlebitis. It is an acidic drug with a pH of 3.5 but once it is injected the charged ring closes and it become lipid soluble= rapid absorption.

32
Q

What are the pharmacokinetic and pharmacological effects of Midazolam?

A

administered IV, IM or orally.
rapidly metabolised - same as diazepam.
similar pharmacological effects as diazepam.

33
Q

What are Benzodiazepam antagonists?

A

Have no intrinsic efficacy but bind to the receptor and prevent interaction between the agonist and the receptor, it is a competitive antagonist.

34
Q

What are some example of benzodiazepine antagonists?

A

Flumazenil (dogs, cattle and sheep) and sarmazenil (maintain anaesthesia with ketamine in horses).

35
Q

What are inverse agonists?

A

Act at the GABA receptor to close the chloride channel and can promote convulsions.

36
Q

What do adrenoreceptors do?

A

They bind circulating catecholamines e.g. NA and A. These bind to a G protein which couples them to the cell. They are classified into a1 and a2.

37
Q

What do the two different subtypes do?

A

a1= stimulated by phenylephrine and antagonised by prazosin
a2= stimulated by clonidine and antagonised by yohimbine.
a2 is also divided into a2a, b and c

38
Q

What do a2 receptors do?

A

they bind to an inhibitory G protein (some bind to a stimulatory G protein) that inhibits adenylate cyclase which decreases cAMP. This reduces Ca influx and increases K out= hyperpolarisation of the membrane and no action potential. They also couple to an H/Na exchanger.

39
Q

Where are alpha2 receptors located?

A

Presynaptically where they block the release of NA. They modulate sympathetic outflow of the CNS. Or post synaptically in arteries and veins where they cause vasoconstriction.

40
Q

What are the three groups within alpha2 agonists?

A

Imidazoles
oxazolines
phenylethylamines

41
Q

How does the selectivity of different alpha 2 agonists vary?

A

Xylazine is less selective for the a2 receptor than the newer agonists e.g. medetomidine.

42
Q

What are the effects of a2 agonists on the CNS?

A

sedation-presynaptic inhibition of NA release
Analgesia- brain, spinal chord, peripheral tissues.
Anaesthesia sparing effect- the minimum alveolar concentration of volatile agents can be reduced by 50-95%.
Muscle relaxation- varies between agents, use prior to ketamine.

43
Q

What is important to remember when using alpha 2 agonists on different species?

A

There is marked species variation in sensitivity. Cattle are 10x more sensitive to xylazine than horses whereas pigs are resistant to a2 agonists. Also dogs can still bite and horses can still kick so combine with an opioid to reduce this.

44
Q

What are the effects of a2 agonists on the CVS?

A

Phase 1: Post synaptic a2 and non selective a1- vasoconstriction and hypertension, an increase in BP= vagally mediated reflex bradycardia.
Phase 2: presynaptic inhibition of NA= decrease in sympatheic outflow= dec HR and vasoconstriction by the nucleus tractus solitarius is the site of a2 agonist drugs.
RESP- mild respiratory depression, depresses the response to hypercarbia, increase in resp. resistance in sheep with xylazine.

45
Q

What are the effects of a2 agonists on the GIT?

A

Vomiting in some species, reduced GIT motility (horses), decreased salivation and reduced gastric secretion.

46
Q

What are the effects of the a2 agonists on the endocrine system?

A

inhibition if ADH promotes diuresis
inhibition of insulin release causes hyperglycaemia
induces the release of growth hormone

47
Q

What are the effects of a2 agonists on the urogenital system and the blood?

A

Induces uterine contraction- (pregnant animals!!)

induces aggregation of platelets

48
Q

What is xylazine and what is it used for?

A

it is an a2 agonist that is licensed for sedation and muscle relaxation in cows, horses, cats and dogs. Used as a pre med prior to ketamine or barbituate induction.

49
Q

What are the different forms of xylazine?

A

virbaxyl and chanazine- for horses only

Rompun (dry that is dissolved)- for horses and zoo animals.

50
Q

How do the effects of xylazine vary by species?

A

Cattle- range of dose for standing and recumbency- IM (5min onset and 10min duration), 24hr rule!!
Horse- IV (onset 5mins, duration 20mins)
Cats and Dogs- reduces doses of barbituates by 50%
Not used in last phase of pregnancy, arrythmogenic

51
Q

What is Detomidine and what is it used for?

A

10mg/ml as a sedative in horses, with opioids to improve the reliability of sedation. Used for pre med prior to ketamine, IM or IV. Compared to xylazine- longer duration, more potent, more ataxia, safer in pregnant animals, but not licensed in cattle.

52
Q

What is romifidine and what is it used for?

A

It is an a2 agonist that is licensed as a sedative, analgesic and as a pre med in horses. Licensed for IV use, less ataxia than xylazine or detomidine, longer duration of action (3hrs) after a high dose.

53
Q

What is Medetomidine and what is it used for?

A

For IM, IV, SC in dogs and cats. Licensed for restraint, sedation, analgesia and pre med in dogs and cats and with butorphenol and ketamine in general anaesthesia.

54
Q

What are the characteristics of Medetomidine?

A

Very potent- highly selective for a2 receptor, max effect is 10-15mins and the duration is dose related (30-180mins), profound anaesthesia sparing effect, NOT for use with CV or resp condition, metabolised in liver and excreted in the kidneys, NOT oral admin- inactivated by the liver.

55
Q

What is Dexmedaetomidine?

A

It is an a2 agonist, isomer of medetomidine. Arrythmic effects, licensed in dogs and cats, short acting so animal will lighten due to sudden loss of anaesthesia sparing effect.

56
Q

What are a2 antagonists?

A

Yohimbine, Tolazoline, Idaxaon they reverse anaesthetic drugs.

Anaesthesia (5 decks)

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