Sedative Drugs Flashcards
Define Premedication
Agent or several agents that are given in preparation of operation or other procedure or treatment (Sedatives, Analgesics and Anticholinergics)
Define Sedation
The act of administering a sedative to achieve a state of calm or sleep. Typically meds used for sedation are given in larger doses than those used for premedication
Define Tranquilizers
Sedate or make calm with the purpose of relieving anxiety or distress
Define Hypnosis
Sleep-like state
note: a patient can be easily roused by hypnotic drugs (unlike narcosis drugs)
Define Narcosis
State of stupor, drowsiness or unconsciousness
note: it is NOT easy to rouse the patient under narcosis (unlike hypnosis)
Name the Phenothiazine drug used as a sedative in animals? (1)
Acepromazine
aka ACE
Name the alpha2 agonist drugs used as a sedative in animals? (5)
- Xylazine, detomidine, romifidine
- Medetomidine and Dexmedetomidine
Name the Butyrophenones drug used as a sedative in animals? (1)
- Azaperone
Name the Benzodiazepam drugs used as a sedative in animals? (2)
- Midazalam, diazepam (valium)
How can Acepromazine be administered to a patient and how long is the onset of action?
- oral tablets/ liquid: unreliable results
- injectable IV/IM: onset 5-20mins IV, and 30-45mins IM
How long can the duration of action of Acepromazine be?
Up to 8 hours
What is the distribution of Acepromazine?
Highly protein bound
- Does cross the BBB
Where in the body is Acepromazine metabolized?
liver via P450
Where in the body is Acepromazine excreted?
Both unconjugated and conjugated metabolites are eliminated in the urine
What is the pharmacodynamics of Acepromazine?
Antagonist of:
Dopaminergic receptor 2 (D2): provides sedative and anti-emetic effects
Histamine receptor1 (H1): provides anti-histaminic effects
Cholinergic muscarinic receptors: provides spasmolytic effect in the GI
Alpha1 receptors in the peripheral vasculature: providing vasodilation
What are 4 sedatives also in the Phenothiazine family of drugs?
- Chlorpromazine
- Promazine
- Methotrimeprazine
- Prochlorperazine
Is Acepromazine considered to be an analgesic?
No! It should never be used for the purposes of pain relief
What are the effects of Acepromazine on the CNS, Cardiovascular System, GIT and histamine response
- CNS: sedation, anti-emesis, extrapyramidal effects (at high doses)
- CVS: hypotension due to vasodilation, and anti-arrhythmic (suppress abnormal arrhythmias)
- GIT: Antispasmodic, reduced LOS tone and increased risk of regurgitation
- Histamine response: anti-histamine effect, which can interfere with an intradermal skin test
note: LOS = lower esophageal sphincter
note: minimal effects on the respiratory system
If Acepromazine were to be given in too high of a dose (overdose), what can be done?
- No reversal agent
- Must combat each of the effects individually: e.g. Alpha1 agonist to combat the vasodilation (e.g. Phenylephrine), or fluid therapy to maintain normal BP
caution: Never use adrenaline as it can worsen vasodilation and drop BP further
What animals is Acepromazine contrindicated in?
- Very sick/ moribund animals
- Animals with an AV-block
- Animals with vasodilation/ syncope
- Very excitable animals (results can be uncertain and may not sedate them)
Why should adrenaline NOT be used to treat acepromazine-induced hypotension?
At low doses, adrenaline has a vasodilating effect because of Beta2 receptor agonism
At which receptors is Acepromazine an antagonist?
Antagonist of: Dopaminergic receptor 2 (D2) Histamine receptor1 (H1) Cholinergic muscarinic receptors Alpha1 receptors in the peripheral vasculature
Name a commonly used sedative that does NOT produce analgesia
Acepromazine
Can Acepromazine be administered to food producing species? Why?
No
Acepromazine can be used in dogs, cats and horses with a passport ONLY
What is the administration routes of the alpha2 agonists used in sedating animals?
- IM, IV, SC, PO, acupuncture needles, intranasal, perineurally and epidurally
What is the distribution of the alpha2 agonists in the body?
- Highly lipophilic
- Cross the BBB
- Highly protein bound
Where in the body are the alpha2 agonists metabolized?
Liver: by P450 pathways
Where in the body are the alpha2 agonists excreted?
- Primarily the kidneys
- the rest in the feces
Where in the body can the different Alpha 2-receptos be found, thus where the alpha2 agonists may take effect?
Alpha2 receptors can be found in: pre, post and extra-synaptic locations
Alpha2a: cerebral cortex, brainstem, locus coeruleus, dorsal horn
Alpha2b: vascular endothelium, thalamus
Alpha2c: spinal cord
Alpha2d: similar to A in location and function
note: the alpha2 agonists bind to the alpha2 receptors mainly on the pre-synaptic locations and inhibit the opening of Calcium channels and inhibiting the excitatory nerve impulses/ release of catecholamines
What are the effects of the Alpha2 agonists on the CNS, Cardiovascular System, GIT, respiratory system, kidney and urethra, and pancreas?
- CNS: profound sedation, anxiolysis and anti-depressant activity, supra-spinal analgesia and centrally-mediated bradycardia
- CVS: peripheral vasoconstriction, increased systemic vascular resistance and hypertension, this then causes a reflexive bradycardia in response to the vascular resistance, thus causing a marked reduction in the cardiac output and corresponding reduction in tissue oxygenation. After the initial hypertension, the body works to reduce the blood pressure to normal levels
caution: the use of anticholinergics to combat the bradycardia can lead to fatal arrythmias
- Respiratory System: reduced RR. In small ruminants profound bronchoconstriction occurs, followed by pulmonary hypertension and pulmonary edema which is usually fatal.
Will also cause profound muscle relaxation, and in brachycephalic breeds muscle relaxation of the head and neck can lead to obstructive airways and an inability to ventilate and oxygenate - Kidney: Anti-ADH effects –> increased urine production
- Urethra: Decreased urethral sphincter tone, which can allow for urine to leak out
- Pancreas: Reduced Insulin secretion leading to hyperglycemia, which can also increase urine production
GIT: Reduced motility, secretions and blood flow to GIT, also reduced LOS tone which can predispose patient to regurgitation
Uterus: stimulate the myometrium and must be avoided in pregnant animals (esp in the 3rd trimester)
Are the alpha2 agonist considered to be an analgesic?
Yes, with primarily spinal origin, they have a synergistic effects with opioids BUT, they are NOT suitable as a sole-analgesic and therefore need to be used as part of a multi-modal approach
What animal species is the alpha2 agonist Xylazine used in?
Cattle: but are very sensitive and require lower doses
Sheep and Goats: Hypoxemia and death can occur
Horses: spasmolytic and analgesic effect good for visceral pain (colic)
What animal species is the alpha2 agonist Detomidine used in?
Horses:
IV = infusion intraoperatively to maintain sedation or for standing sedation
Oral = for minor handling procedures like clipping
Cattle: sedation
note: can be used on pregnant animals
caution: not to be used with potentiated sulphonamides in horses as it can cause cardiac arrhythmias
What animal species is the alpha2 agonist Romifidine used in?
Horses: longest duration of action and provides the least amount of ataxia in horses and is often used intraoperatively
What animal species is the alpha2 agonist Medetomidine and Dexmedetomidine used in?
Small animals: have profound CVS effects (vasoconstriction, hypertension, bradycardia) which can deter vets
Can also cause vomiting
BUT are considered analgesic and appropriate for multi-modal analgesic protocols
What animals should you avoid alpha2 agonist in?
- Any animal with cardiac disease e.g. bradycardia or arrhythmias
- Pregnant animals
- Moribund or very sick animals
What happens if an animal has an overdose of alpha2 agonist?
- Can be reversed! Atipamezole (Antisedan)
other reversal agents include Yohimbine and Tolazoline