Test 2- Drugs Acting on the Central Nervous System Flashcards
Tranquilizer
nduces a state of behavioral change wherein anxiety is relieved and the patient is relaxed although aware of their surroundings.
Sedative:
Induces a state characterized by CNS depression and drowsiness, decreased awareness of surroundings.
Hypnotic:
Produces sleep.
Narcotic:
Produces stupor bordering on general anesthesia. This state used to be produced with opium which is why morphine type drugs are called ‘narcotics’ in law enforcement.
Note: In veterinary practice the distinction is usually not clear so for our purposes we will use the term ‘sedative’ for all of these although we may discuss the differences when comparing specific drugs. For example benzodiazepines cause more anxiety reduction than drowsiness, while phenothiazines cause more drowsiness.
Local/regional anesthesia:
Loss of sensation in a circumscribed body area (this is covered more in the ‘local anesthetics’ section).
General anesthesia
Drug-induced unconsciousness characterized by controlled, reversible depression of the CNS and analgesia. The patient cannot be aroused. Sensory, motor and autonomic reflexes are reduced.
Dissociative anesthesia:
Dissociation of the thalamocortical and limbic systems resulting in a catatonic state where the eyes remain open and swallowing reflexes remain functional. Skeletal muscles maintain tone.
for a drug to have a direct action on the CNS it needs to
so for a drug to have a direct action on the CNS it needs to get past the BBB. Typically lipophilic drugs that can cross cell membranes are better able to do this, as long as they are not specifically kept out (eg. P-glycoprotein pump).
Most drugs that cause sedation/anesthesia likely work by
Most drugs that cause sedation/anesthesia likely work by reducing input to the ascending reticular activating system (ARAS) which is the part(s) of the brain thought to be involved in consciousness.
Excitatory Neurotransmitters
- Excitatory (drugs may depress the CNS by suppressing these transmitters or blocking their receptors)
o Glutamate – stimulates the NMDA receptor
o Acetylcholine – stimulates neuronal nicotinic receptors o 5-HT3 (serotonin) – stimulates 5-HT3 receptors
Inhibitory Neurotransmitters
- Inhibitory (drugs may depress the CNS by mimicking these neurotransmitters or enhancing their receptors)
o GABA
o Glycine
A number of neurotransmitters are metabolized by
A number of neurotransmitters are metabolized by monoamine oxidase (MAO) and thus will be affected by drugs that alter MAO or drugs that act directly on their receptors as agonists or antagonists. This is the primary mechanism for several of the drugs we will discuss. If a drug has effects at more than one receptor (which is pretty common) focus on the primary mechanism of action.
o Dopamine o Norepinephrine (NE) o Serotonin (5-HT) o Histamine (H)
Analgesia alone is needed
Analgesia alone is needed in a number of situations and CNS drugs (especially opioids) may be combined with other drugs (e.g. NSAIDs) to achieve this purpose.
Sedation alone may be needed for
Sedation alone may be needed for patients with anxiety disorders or aggression to facilitate handling, travel in the car, thunderstorms, etc.
Muscle relaxation alone may be needed
Muscle relaxation alone may be needed in cases where there is abnormal muscle tension (eg. reducing a hip luxation, certain toxins). Muscle relaxants will usually be used with other agents in these cases depending on the specific needs.
Analgesia and sedation may be needed for
Analgesia and sedation may be needed for minor, painful procedures (e.g. Small biopsy)
Sedation with muscle relaxation but no analgesia may be good for
Sedation with muscle relaxation but no analgesia may be good for nonpainful procedures (e.g. Ultrasound, radiographs).
Reduced consciousness, muscle relaxation and analgesia together are usually desired for
Reduced consciousness, muscle relaxation and analgesia together are usually desired for general anesthesia for any sort of procedure or surgery.
There is sometimes overlap between
There is sometimes overlap between anesthetic/sedative drugs and anticonvulsant drugs.
When considering treatment of seizures in acute/severe seizure conditions (e.g. status epilepticus or toxins) the drugs used will
When considering treatment of seizures in acute/severe seizure conditions (e.g. status epilepticus or toxins) the drugs used will overlap significantly with anesthetic drugs and
indeed, general anesthesia is sometimes necessary in those cases.
When treating chronically (e.g. idiopathic epilepsy)
When treating chronically (e.g. idiopathic epilepsy) then a different set of medications are used, those are typically orally administered and they will be discussed in their own section later on.
Opioid:
Agonist at opioid receptors (anything that can be displaced by naloxone)
Opiates:
Naturally occurring drugs (alkaloids) extracted from opium
Narcosis:
A stupor bordering on general anesthesia (used to be induced with opium, hence morphine- type drugs are called ‘narcotics’ in law enforcement.
Natural opiates:
Alkaloids from the seed pods of opium (Papaver somniferum) – eg. Morphine
Semisynthetic opioids:
Substitution of chemical radicals in the place of hydrogen atoms at the hydroxylpositions of morphine – eg. oxymorphone, hydromorphone, apomorphine
Synthetic opioids:
Completely manufactured in a lab – eg. Fentanyl, carfentanyl, butorphanol
neuroleptanalgesia
Opioid drugs are important and very commonly used in veterinary medicine. They are very good analgesics and also provide varying degrees of sedation. When combined with other sedatives (alpha-2 agonists, benzodiazepines, phenothiazines) a synergistic effect is seen resulting in very good sedation – this is called ‘neuroleptanalgesia’.
