Anesthesia DRUGS

Which group of drugs is reversed by naloxone?

Opioids

Which group of drugs is reversed by flumazenil?

Benzodiazepines (BZD)

Which group of drugs is reversed by atipamezole?

Alpha 2 agonists

What is a phenothiazine used for sedation (in combination with an opioid) and long sedation

Acepromazine

In which animals must you use acepromazine with caution in?

Boxers (bradycardia and hypotension), giant breed and stallions, dehydrated hypovolemic and hypotensive patients

What is the mechanism of action of acepromazine?

D1, D2, ⍺1, 5- HT2, M3, H1 antagonist

What is the onset of action of acepromazine

20 to 40 min (IM)

10 to 15 min (IV)

30 to 60 min (PO)

What is the duration of action of acepromazine?

4 to 6 hours

What are side effects of acepromazine?

CNS depression, Vasodilation, antiemetic, transient ↓ PCV (RBC sequestration in the spleen), interference with platelet aggregation (antithrombic), platelet sequestration in the spleen, antiarrhythmic, antihistaminic, reduces lower gastroesophageal sphincter tone (reflux)

Does acepromazine cause analgesia?

No

When can acepromazine be used in recovery?

At low doses to help manage opioid-induced dysphoria in the recovery period (cats and dogs)

What are some alpha 2 agonist that can be used for sedation, muscle relaxation, and analgesia (in combination with an opioid)

Dexmedetomidine, medetomidine, xylazine

When should alpha 2 agonist be used in caution?

Cardiac patients, pediatric, old, critically ill patients

Why isn’t xylazine used as much anymore?

Because it is less selective for alpha 2 as some of the other alpha 2 agonist on the market

What is the onset of action of the alpha 2 agonists discussed

10 to 15 min (IM)

3 min (IV)

What is the duration of action of the alpha agonist discussed

1-1.5 hrs

What are side effects of alpha 2 agonists

CNS depression Vasoconstriction (hypertension), bradycardia, ↓cardiac output (hemodynamic biphasic effect), 1st and 2nd degree AV blocks, emetic, ↑ urine production (decreased ADH and renin secretion), ↓ insulin secretion, paradoxical excitement due to high levels of circulating catecholamines, delayed action of induction agents, reduces lower gastroesophageal sphincter tone

Describe the phases of the biphasic hemodynamic effect of alpha 2 agonists

Phase I (around 20 mins): peripheral vasoconstriction (⍺2 -mediated) and hypertention then reflex bradycardia (baroreceptors)

Phase II: blood pressure returns back to normal, but bradycardia remains due to presynaptic CNS effects

Which drug reverses sedative analgesic and cardiovascular effects of alpha 2 agonists

Atipamezole (IM) (ANTISEDAN)

Which drug reverses only cardiovascular effects of alpha 2 agonists

Vatinoxan (IM)

What is the onset and duration of action of atipamezole?

Onset: 5 to 10 minutes

Duration: 1 to 2 hours

What is the onset and duration of action of vatinoxan?

Onset: 5 to 15 minutes

Duration: 45 minutes

What are some benzodiazepine drugs used as a tranquilizer, anxiolytic sedative (pediatric, geriatric, ill patients), muscle relaxant, or coinductor

Midazolam and diazepam

What is the mechanism of action of benzodiazepines (midazolam and diazepam)?

GABA positive modulator

Do benzodiazepines provide analgesia?

No

Why should benzodiazepines be given with another drug in young healthy patients?

Alone they produce very mild or no sedation in healthy cats and dogs and can even cause excitation due to loss of learned inhibitory behavior

What is the onset of action of midazolam?

5 to 10 min (IM)

1 to 3 min (IV)

What is the onset of action of diazepam?

1 to 3 min (IV)

What is the duration of action of benzodiazepines?

1 to 2 hours

What are the side effects of benzodiazepines?

CNS depression, paradoxical excitation, anticonvulsant and MAC sparing effect

Which opioids are full µ, κ, δ agonists and can be used for analgesia of moderate to severe pain

Morphine, hydromorphone, meperidine, fentayl

Which opioid is full µ, κ, δ agonists and NMDA antagonist used for analgesia of moderate to severe pain

Methadone

What is the onset of action of morphine?

5 to 15 min (IV) (slowly)

15 to 45 min (IM)

What is the onset of action of hydromorphone?

15 min (IM)

What is the onset of action of methadone?

3 min (IV)

5 to 10 min (IM)

What is the onset of action of fentanyl?

1 to 2 min (IV)

What is the duration of action of morphine?

4 to 6 hours

What is the duration of action of hydromorphone?

3 to 5 hours

What is the duration of action of methadone?

2 to 4 hours

What is the duration of action of fentanyl?

20 min

What are some side effects of morphine?

↓HR, ↓RR, emetic, constipation, panting, miosis/mydriasis, hypothermia in dogs/hyperthermia in cats, dysphoria, euphoria, urinary retention

What are some side effects of hydromorphone?

↓HR, ↓RR, emetic, constipation, panting, miosis/mydriasis, hypothermia in dogs/hyperthermia in cats, dysphoria, euphoria

What are some side effects of methadone?

↓HR, ↓RR, constipation, panting, miosis/mydriasis, hypothermia/hyperthermia, dysphoria, euphoria

What are some side effects of fentanyl?

↓HR, ↓RR, miosis/mydriasis, hypothermia/hyperthermia, dysphoria, euphoria

Which opioid can also be used as a co-inducer?

Fentanyl

Which opioid is a partial µ agonist, weak κ antagonist used for analgesia (post operative or minor procedures)

Buprenorphine

What is the onset of action of buprenorphine?

20 to 45 min (IM)

20 min (IV)

What is the duration of action of buprenorphine?

4 to 6 hours

What are some side effects of buprenorphine?

Minimal sedation, moderate analgesia, rare respiratory depression

What is important to consider with buprenorphine if the analgesic effect doesn’t seem to be enough for the patients pain?

It has a high affinity for opioid receptors so if you try to give a full agonist to increase analgesia it will be ineffective

Which opioid is a partial µ antagonist and 𝜅 agonist which has poor analgesia and partial reversal so it is only used for diagnostic procedures and bronchoscopies

Butorphanol

What is the onset of action of butorphanol?

1 to 3 min (IV)

10 to 15 min (IM)

What is the duration of action of butorphanol?

1 to 2 hours

Which drug is a serotonin 2A antagonist and reuptake inhibitor which is used for sedation and anxiety relief

Trazadone

What is the onset of action of trazadone?

30-60 min (PO)

What is the duration of action of trazadone?

4 hrs

What are some side effects of trazadone?

Aggressive food seeking, sedation, diarrhea, nausea

What is a barbiturate used for induction?

Thiopental

What is the mechanism of action of thiopental?

GABA agonist

What is the onset of action of thiopental?

20 to 30 sec (IV)

What is the duration of action of thiopental?

10 to 15 min

Which animals is thiopental a poor choice in?

Greyhounds (cardiac depression and long recovery) and hemodynamically compromised patients

What are some side effects of thiopental?

CNS depression, dose and rate dependent cardiovascular and respiratory depression/apnea, cardiac arrhythmias (PVCs, bigeminy), ↓ ICP and oxygen requirements of the brain, not suitable for CRI

What is the only induction drug talked about that produces analgesia?

Ketamine

What is the mechanism of action of propofol?

GABAa enhancer and NMDA antagonist

What is the onset of action of propofol?

30-60 sec (IV)

What is the duration of action of propofol?

10-15 min

What are some side effects of propofol?

Depression of the CNS, dose and rate dependent cardiovascular (hypotension, ↓ CO) and respiratory depression/apnea, ↓ ICP and oxygen requirements of the brain, muscle relaxation, myoclonus, nystagmus, opisthotonus

When can you use propofol?

Induction (acceptable for C-section), Maintenance (TIVA), Anticonvulsant (CRI), Head trauma

Which form of propofol is only approved for dogs and is not suitable for CRI

Multidose (benzyl alcohol) (the one with the longer shelf life)

Why can you not use propofol as a CRI in cats

They are prone to heinz body anemia and decreased PCV from altered metabolism

Which animals should you use propofol with caution in?

Animals hemodynamically compromised and pancreatitis (lipid emulsion)

What is the mechanism of action of etomidate?

GABA agonist

What is the onset of action of etomidate?

60 sec (IV)

What is the duration of action of etomidate?

10-20 min

When is etomidate used?

Induction in combination with a BZD or fentanyl

Patients with low cardiac reserve and hypovolemia

What are some side effects of etomidate?

CNS, depression, dose and rate dependent respiratory depression/apnea, high incidence of myoclonus, inhibition of adrenal steroid synthesis (aldosterone, cortisol and corticosterone) for 2 to 6 hours with one single dose

When should you use etomidate with caution

Avoid in animals with known adrenal insufficiency (unless cortisol supplementation is provided)

What is the mechanism of action of alfaxalone?

GABA agonist

What is the onset of action of alfaxalone?

60 sec (IV)

What is the duration of action of alfaxalone?

10 min

What are some side effects of alfaxalone?

CNS depression, dose and rate dependent cardiovascular (hypotension, ↓ CO) and respiratory depression/apnea (less than propofol), myoclonus and opisthotonus during cat’s recovery (add sedative)

When is alfaxalone used?

Induction, maintenance, C-section

In which animals should you be cautious to use alfaxalone in?

Hemodynamically compromised

What is the mechanism of action of ketamine

NMDA and glutamate antagonist

µ, 𝜅, 𝛿 agonist

GABA agonist like

⍺1 and β2 interactions

What is the onset of action of ketamine?

5 to 10 min (IM)

60 to 90 sec (IV)

What is the duration of action of ketamine?

30 to 45 min

What is ketamine used for?

Induction( with propofol or BZD), maintenance (TIVA), analgesia (CRI), chemical restrain (with ⍺2 and opioids for sedation)

What is a FDA schedule III drug which causes functional disorganization of CNS, desocialization between the limbic and thalamocortical system

Ketamine

What are side effects of ketamine?

Amnesia, muscle rigidity, maintained reflexes (without their protective function), ↑HR, BP, ICP, IOP, inotropism and CO, bronchodilation, apneustic pattern (abnormal breathing pattern), decreased inotropism in patients adrenally depleted, accumulation after repeated administration or TIVA

Which patients should ketamine be used with caution in or not at all?

Hypertrophic cardiomyopathy and critically ill patients, head trauma (↑ ICP), C-section (associated with increased maternal and fetal mortality and decreased neonatal vigor compared to other options), cats with kidney disease (reduce the dose)

Why must the dose of ketamine be lowered for cats with kidney disease?

Because the active metabolite norketamine will stay in the system for longer because of impaired excretion

Which other drug beside ketamine causes functional disorganization of CNS (desocialization between the limbic and thalamocortical system) and has some analgesic effect?

Tiletamine-zolazepam (Tilazol)

What is the mechanism of action of tilazol?

Tiletamine- NMDA antagonist

Zolazepam- GABAa positive modulator

What is the onset of action of tilazol?

5 to 10 min (IM)

60 to 90 sec (IV)

What is the duration of action of tilazol?

30 to 60 min

What are side effects of tilazol?

Can cause cardiac depression at high dose, same neurological effects, more respiratory depression compared to ketamine, muscle rigidity, excitation and seizure-like activity during recovery in dogs, do not redose (prolonged and rough recoveries)

Which patients should tilazol be used with caution in?

Head trauma, hypertrophic cardiomyopathy, and critically ill patients

What is tilazol used for?

Induction (with propofol or BZD), chemical restrain, heavy sedation for diagnostic procedures

What is the MAC of isoflurane? What does this mean?

1.3-1.6

Since the MAC of iso is lower than sevo it is more potent compared