Phenothiazines Flashcards
(30 cards)
What are Phenothiazines?
- Pre-meds that provide Tranquilisation, with sedation - at higher doses
- Dopamine receptor antagonists that have a calming effect
True or False.
Phenothiazines provide analgesia.
False.
Phenothiazines do not provide any analgesia.
Can Phenothiazines be used synergistically with Opioids?
Yes
If dopamine is the happy hormone, how do phenothiazine’s act of antagonising the dopamine receptors make veterinary patients sedated?
- It’s a paradox!
- But essentially Dopamine is a motivation, reward + alertness neurotransmitter
- So it helps regulate wakefulness, motor activity, attention + arousal - not just happiness
- So as Dopamine receptor antagonists in the CNS, they block transmission of:
- Alertness + motivation drop
- Motor activity decrease (Dopamine is key for these)
- Sedation (Brain becomes less responsive to stimulation)
- Essentially turning down the Dopamine signals
- Making the patient less responsive to their environment + less motivated to move - making them sleepier/sedatwed
- Dopamine promotes alertness > Phenothiazines block Dopamine > less alertness = Sedation
Explain in basic terms how Phenothiazine’s ability to block Dopamine recepetors
- Dopamine promotes alertness >
- Phenothiazines block Dopamine >
- Less alertness = Sedation
How do Phenothiazines cause sedation, in comparison the GA, which causes a loss of conciousness?
- Phenothiazines only block Dopamine + few other neurotransmitters which lower arousal + anxiety, but don’t completely shut down the brain’s consciousness pathways
- GA affects much deeper brain circuits, mostly the Reticular Activiating System (RAS) in the brainstem - boosting the GABA (Inhibitory) neurotransmitter, causing a full ‘switch-off’ of awareness
ESSENTIALLY…..
* I.e; Phenothiazines sedate because they don’t suppress deep enough in the brain centers that control consciousness, they just calm things down
Name the most common Phenothiazine
Acetylpromazine
(ACP)
Name the only licensed Phenothiazine used as anaesthesia for patients in the VP
Acetylpromazine
(ACP)
True or False.
ACP is usually used in combo with other Opioids.
True
Name the 2 forms that ACP is administered to patients as
- Tablet
- Injectable
What effects does ACP have on the patient?
- Tranquaillisation
- Sedation
True or False.
Phenothiazines, such as Acetylpromazine has a long duration of action.
True
How long is ACP’s duration of action for?
Up to 6 hrs
Do Phenothiazines generally have a stormy or smooth recovery?
Smooth, especially if used synergistically with Opioids
Are Phenothiazines relatively safe for the CVS?
Yes, as they have a protective effect against arrhythmias - at standard doses
Why are Phenothiazines realtively safe for the CVS?
Because they have a protective effect against arrhythmias
Provide the long version of why the Phenothiazine, Acetylpromazine protects the body from arrhythmias
Basically how they effect the SNS + heart’s eletrical stability…
Step 1. Reduced Sympathetic Tone
1. ACP blocks the Alpha-1-Adrenergic receptors
2. Leading to vasodilation + drop in BP
3. When BP drops, the SNS kicks in w/a surge of Adrenaline (Catecholamines like epinephrine + norepineephrine)
4. BUT
5. ACP dampens the effects of the Catecholamines on the heart, due to the alpha-blocking action
Step 2. Membrane-Stabilizing Effects
1. Some Phenothiazines have mild direct effects on the heart cell membranes (cardiac myocytes)
2. They slightly stabilize the Sodium ion channels
3. Helping prevent erratic firing action potentials
4. This results in a more stable cardiac eletrical conduction
5. Meaning, less chance of abnormal beat
Step 3. Anxiolysis (Calming)
1. By calming the patient (reducing anxiety, stress + excitement)
2. ACP indirectly lowers the endogenous catecholamine surges
3. This is important, because stress alone can provoke arrhythmias in sick + anaesthetized animals
Acetylpromazine has a protective effect against arrhythmias by reducing the sympathtic tone, stabilising the cardiac membrane and calming the patient.
Explain how ACP reduces Sympathetic Tone.
- ACP blocks the Alpha-1-Adrenergic receptors
- Leading to vasodilation + drop in BP
- When BP drops, the SNS kicks in w/a surge of Adrenaline (Catecholamines like epinephrine + norepineephrine)
- BUT
- ACP dampens the effects of the Catecholamines on the heart, due to the alpha-blocking action
Acetylpromazine has a protective effect against arrhythmias by reducing the sympathtic tone, stabilising the cardiac membrane and calming the patient.
Explain how ACP stabilises the Cardiac Membrane.
- Some Phenothiazines have mild direct effects on the heart cell membranes (cardiac myocytes)
- They slightly stabilize the Sodium ion channels
- Helping prevent erratic firing action potentials
- This results in a more stable cardiac eletrical conduction
- Meaning, less chance of abnormal beat
Acetylpromazine has a protective effect against arrhythmias by reducing the sympathtic tone, stabilising the cardiac membrane and calming the patient.
Explain how ACP calms the patient.
- By calming the patient (reducing anxiety, stress + excitement)
- ACP indirectly lowers the endogenous catecholamine surges
- This is important, because stress alone can provoke arrhythmias in sick + anaesthetized animals
Essentially, how does ACP protect the CVS from arrhythmias?
- By blocking the effects of Adrenaline
- Stabilizing the cardiac membranes a little + reducing stress
- Which reduces the electrical instability of the heart
True or False.
ACP isn’t generally safe for the respiratory system and should take extreme care when providing standard doses to patients with respiratory comprimise.
False!
ACP is generally safe for the respiratory system, at standard doses!
List the 3 side effects of ACP on the body
- Anti-emetic
- Smooth muscle relaxation (Gut + urethra)
- Mild anti-histamine effect
How does ACP work as an anti-emetic?
It binds with same receptors as Metoclopramide!
