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Drugs > Alpha 2 Agonists and Antagonists > Flashcards

Alpha 2 Agonists and Antagonists Flashcards

1
Q

What are alpha2 agonists commonly used for

A

sedation and pre-anesthetic medication

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2
Q

Are alpha2 agonists reversible?

A

Yes

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3
Q

What is an overview of the mechanism of action for alpha2 agonists?

A

They bind to alpha2 and alpha1 adrenergic receptors (adrenoceptors).

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4
Q

What is the alpha2 to alpha1 ratio for dexmedetomidine?

A

1620:1

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5
Q

What is the alpha2 to alpha1 ratio for medetomidine?

A

1620:1

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6
Q

What is the alpha2 to alpha1 ratio for romifidine?

A

340:1

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7
Q

What is the alpha2 to alpha1 ratio for detomidine?

A

260:1

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8
Q

What is the alpha2 to alpha1 ratio for clonidine?

A

220:1

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9
Q

What is the alpha2 to alpha1 ratio for xylazine?

A

160:1

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10
Q

How many alpha2 subtypes have been identified?

A

Three: alpha2A, alpha2B, alpha2C

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11
Q

Are there any other alpha2 subtypes that have been identified?

A

Yes, in some species: cattle, and rats, an alpha2D receptor has been identified that functions similarly to alpha2A

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12
Q

What is the mechanism of action of an alpha2 agonist?

A

So it binds to the adrenoceptors which are G-protein coupled receptors with an inhibitory action.

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13
Q

What happens when you activate an adrenoceptor?

A

inhibition of cAMP production, a decrease in cellular activity, cellular hyperpolarization

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14
Q

How does cellular hyperpolarization occur when an adrenoceptor is activated?

A

inhibition of voltage-gated Ca2+ channels and stimulation of inwardly rectifying K+ channels

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15
Q

What kind of effect do alpha2 agonists have within the CNS?

A

antisympathetic

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16
Q

where are alpha2 adrenoceptors located?

A

in the CNS and PNS as well as other tissues and organs

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17
Q

Are alpha2s pre or post-synaptic?

A

They can be both

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18
Q

What kind of receptors are presynaptic alpha2s?

A

autoreceptors and heteroreceptors

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19
Q

what kind of effects do autoreceptor alpha2s have?

A

adrenergic effects - norepinephrine

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20
Q

What kind of effects to heteroreceptor alpha2s have?

A

non-adrenergic effects - serotonin, GABA, acetylcholine

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21
Q

What kind of effects do alpha2s have on the nervous system?

A

sedation, hypothermia, muscle relaxation (can lead to ataxia/recumbency)

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22
Q

How do alpha2s cause sedation?

A

they activate the alpha2 receptors in the locus coeruleus in the brain

23
Q

Where is analgesia “induced” in the CNS

A

the brainstem and dorsal horn of the spinal cord. Analgesia is co-localized with opioid receptors, potential for synergy

24
Q

What are the initial CV effects of an alpha2?

A

vasoconstriction, increased SVR, baroreceptor-mediated bradycardia, decreased CO

25
Q

What is the secondary CV effects of an alpha2?

A

decreased sympathetic tone via central effects, peripheral vasodilation, bradycardia

26
Q

What kind of arrhythmias can you see with alpha2s?

A

sinus bradycardia, profound sinus arrhythmia in some species, first and second-degree AV block

27
Q

What kinds of effects can you see on the respiratory system secondary to alpha2 administration?

A

decreased respiratory rate, central ventilatory drive is decreased in dogs, upper airway resistance increases in horses

28
Q

Does hypoxemia occur with alpha2 administration?

A

generally very minimally

29
Q

Of all the species, which one is more sensitive to the respiratory effects of alpha2s?

A

ruminants

30
Q

What happens to sheep when you give an alpha2?

A

hypoxemia! D/t pulmonary hypertension and interstitial edema

31
Q

What are the renal effects of an alpha2 administration?

A

renal blood flow decreases, decreases in ADH results in diuresis

32
Q

What are the endocrine effects of an alpha2 administration?

A

decreased stress response, decreased insulin release, can lead to hyperglycemia and osmotic diuresis

33
Q

What are the GI effects of alpha2 administration?

A

relaxed LES, vomiting, nausea, inhibition of gastric emptying, decreased intestinal motility

34
Q

What is clonidine used for in dogs?

A

An oral anxiolytic

35
Q

What pharmacological profile do you need to be aware of with clonidine?

A

highly lipid soluble, large volume of distribution, two compartment model, centrally-mediated hypotensive effects will predominate

36
Q

What kind of hypotensive effects are seen with clonidine?

A

Centrally-mediated hypotensive effects predominate

37
Q

What pharmacological profile do you need to be aware of with xylazine?

A

Highly lipid soluble, large volume of distribution

EXTENSIVE liver metabolism, phase I transformation via CYP3A microsomes

38
Q

In what species is xylazine particularly used in?

A

Equines! Sedation, short-term analgesia, and a preanesthetic

39
Q

Does xylazine result in increased uterine tone?

A

Yes.

40
Q

What species is the most sensitive to xylazine? The least sensitive to xylazine?

A

Most = cattle
Least = pigs

41
Q

Where is detomidine metabolised?

A

Liver

42
Q

Which has the longer duration of action: xylazine or detomidine?

A

Detomidine

43
Q

What is medetomidine a derivative of?

A

detomidine

44
Q

How and where is medetomidine metabolised?

A

liver metabolism via hydroxylation and conjugation in DOGS. the hydroxylated compound is excreted in urine in cats (as they are glucuronide deficient)

45
Q

Dexmedetomidine is the inactive enantiomer of medetomidine - T or F?

A

FALSE! Dexmedetomidine is the active enantiomer of medetomidine

46
Q

How and where is dexmedetomidine metabolised?

A

Liver metabolism via hydroxylation and glucuronidation (species differences in efficiency)

47
Q

What are the pharmacological profile highlights of romifidine?

A

similar duration of action to detomidine, marketed for horses in the US, may produce less ataxia compared to other alpha2s in equines

48
Q

Where is romifidine metabolised?

A

liver metabolism and renal excretion

49
Q

What is the alpha2 to alpha1 ratio of yohimbine?

A

40:1

50
Q

Does yohimbine have a large or small volume of distribution?

A

LARGE volume of distribution, but a relatively slow clearance

51
Q

What happens when yohimbine is used as an alpha2 reversal in cats/dogs?

A

sedation may be incompletely reversed, side effects: dysphoria, vocalization, GI effects are reversed

52
Q

What can be seen with yohimbine administration in equines?

A

respiratory distress, tachycardia, and death have been seen in equines after IV administration. IM administration is recommended

53
Q

Which reversal has the lowest affinity for alpha2 receptors?

A

Tolazoline

54
Q

What negative effect can be seen in camelids that receive tolazoline?

A

death

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