Neuropharmacology Quiz TRUE

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Questions and Answers

What characteristic of drugs allows them to cross the blood-brain barrier (BBB) most effectively?

Large molecular size

High protein binding

Lipid solubility (correct)

Ionized at physiological pH

Which neurotransmitter is NOT typically associated with the central nervous system?

Acetylcholine

Epinephrine (correct)

Glycine

Histamine

What role do second messengers play in the neurotransmitter–receptor complex?

They amplify the cellular response to drug-receptor binding. (correct)

They directly alter membrane potential by opening ion channels.

They prevent receptor activation from occurring.

They bind to neurotransmitters to enhance synaptic transmission.

Which of the following is a common effect that drugs acting on the central nervous system can produce?

Tranquilization (sedation) Signup and view all the answers

How does inflammation affect the permeability of the blood-brain barrier?

It increases permeability, allowing easier drug access. Signup and view all the answers

What significantly limits the use of diazepam as a maintenance anticonvulsant in dogs?

Development of tolerance due to drug metabolism Signup and view all the answers

Which benzodiazepine is known for having the shortest elimination half-life in dogs?

Midazolam Signup and view all the answers

What is a potential adverse effect of diazepam after administration?

Irritability and depression Signup and view all the answers

Which of the following statements about clonazepam is correct?

Tolerance develops rapidly, limiting its effectiveness. Signup and view all the answers

What distinguishes midazolam's pharmacokinetic profile from diazepam?

It crosses the blood-brain barrier more readily. Signup and view all the answers

Which of the following therapeutic uses is NOT associated with midazolam?

Long-term maintenance anticonvulsant Signup and view all the answers

How does GABA affect neuronal activity when activated by benzodiazepines like diazepam?

It promotes hyperpolarization of the neurons. Signup and view all the answers

What is a significant adverse effect associated with the use of Br− in cats?

Severe asthma Signup and view all the answers

Which of the following is a potential gastrointestinal adverse effect of valproic acid in dogs?

Diarrhea Signup and view all the answers

What is the primary mechanism of action of gabapentin?

Inhibiting voltage-dependent Ca2+ channels Signup and view all the answers

Which anticonvulsant is described as structurally unrelated to other anticonvulsants?

Valproic acid Signup and view all the answers

Which of the following adverse effects is specifically noted for gabapentin?

Abrupt withdrawal leading to seizures Signup and view all the answers

What is the recommended use of levetiracetam in veterinary medicine?

As an adjunctive therapy for refractory canine epilepsy Signup and view all the answers

Which adverse effect is consistent with the use of Br−?

Irritability and aimless walking Signup and view all the answers

Which statement is true regarding the clinical use of valproic acid in cats?

Its clinical usefulness has not been evaluated Signup and view all the answers

Which side effects are identified for valproic acid in dogs?

Vomiting, anorexia, and potential liver failure Signup and view all the answers

What is the primary mechanism of action of levetiracetam?

Binding to synaptic vesicle protein 2A Signup and view all the answers

Which of the following is NOT a common adverse effect of levetiracetam?

Liver dysfunction Signup and view all the answers

Felbamate should be avoided in which condition in dogs?

Liver disease Signup and view all the answers

What is an effect of zonisamide on neurons?

Induction of hyperpolarization Signup and view all the answers

What is the primary therapeutic use of doxapram in veterinary medicine?

To arouse animals from anesthesia Signup and view all the answers

Which of the following statements about felbamate is true?

It can be used as a sole anticonvulsant agent. Signup and view all the answers

What should be noted about the administration of zonisamide?

It is administered orally twice daily. Signup and view all the answers

Which of the following side effects is rarely associated with felbamate in dogs?

Keratoconjunctivitis sicca Signup and view all the answers

What is a potential consequence of abruptly withdrawing levetiracetam?

Increased seizure frequency Signup and view all the answers

Study Notes

Drugs Acting on the Central Nervous System

Drugs can alter CNS function to produce anticonvulsant effects, tranquilization (sedation), and analgesia.
Neurotransmitters in the CNS include dopamine, GABA, acetylcholine, norepinephrine, serotonin, histamine, glutamate, glycine, substance P, and many neuropeptides.
Neurotransmitters combine with receptors on the postsynaptic neuron, altering its membrane potential.
Receptors for neurotransmitters are the site of action for exogenous drugs.
Neurotransmitter-receptor complexes can directly alter cell membrane permeability.
Second messengers initiate chemical reactions altering ion transport and membrane potential.
Second messenger systems amplify cellular response to drug-receptor binding.
Most neurotransmitters have G protein-coupled receptors (GPCRs).
Circulating drugs must cross the blood-brain barrier (BBB) to reach brain neurons.
Drugs that readily cross the BBB are lipid-soluble, small, poorly bound to protein, and nonionized at the CSF pH.
The BBB becomes more permeable in the presence of inflammation or tumors.
The BBB is poorly developed in neonates.
Only a few anticonvulsant drugs are clinically useful in dogs and cats.
Some drugs are metabolized too rapidly in dogs to be effective, even at high dosages.
Cats generally metabolize drugs more slowly than dogs.
Anticonvulsant drugs stabilize neuronal membranes.
They may act directly on ion channels, resulting in hyperpolarization.
They activate GABA-gated Cl- channels, increasing the frequency of Cl- channel opening.
Anticonvulsants reduce incidence, severity, and duration of seizures.
Seizures or status epilepticus may follow rapid cessation of administration.
Adverse effects include enzyme induction and hepatotoxicity.

Barbiturates

Phenobarbital is an oxybarbiturate.
Barbiturates activate GABA-gated Cl- channels, evoking hyperpolarization of neurons.
Phenobarbital limits the spread of action potentials and elevates the seizure threshold.
It is used for long-term seizure control.
It's administered orally; GI absorption is complete, and peak levels occur in 4-8 hours in dogs.
It is not effective for terminating ongoing seizures due to a long onset of action.
Adverse effects include sedation, polydipsia, polyuria, and polyphagia.
Dogs develop tolerance to sedative effects after 1-2 weeks.

Primidone

Primidone is a deoxybarbiturate analog of phenobarbital.
It is slowly absorbed in dogs.
Cats metabolize primidone to phenobarbital more slowly.
Prolonged use may lead to decreased serum albumin and elevated liver enzyme concentrations.
Serious liver damage can occasionally occur.

Pentobarbital

Pentobarbital is an oxybarbiturate and terminates seizures at a dose that induces anesthesia.
This dose causes significant cardiopulmonary depression, though may be the only way to control status epilepticus.
It has a rapid onset (<1 minute) after IV injection and short duration of action.
It's a CNS depressant and may irritate when administered perivascularly.
The use of IV pentobarbital is the most reliable method of controlling status epilepticus in veterinary medicine.

Phenytoin

Phenytoin is a hydantoin derivative.
It stabilizes neuronal membranes and limits seizure activity.
It reduces Na+ influx during action potentials, Ca2+ influx during depolarization, and promotes Na+ efflux.
K+ movement out of the cell during action potentials may be delayed, increasing the refractory period.
It's an anticonvulsant drug, but impractical in dogs due to its short half-life.
It's recommended for digitalis-induced ventricular arrhythmias in dogs.

Benzodiazepines

Diazepam, midazolam, clonazepam, and lorazepam are anticonvulsants, used to treat status epilepticus.
They can be used as maintenance anticonvulsants in cats due to their relatively slower metabolism.
They are rarely used maintenance anticonvulsants in dogs because of drug tolerance development.
Diazepam mechanism of action involves activating GABA-gated Cl- channels, potentiating channel opening, and inducing neuronal hyperpolarization.
In cats, oral administration is useful for seizure control, though tolerance development can occur.
In dogs, IV administration controls status epilepticus, and cluster seizures, as well as maintenance anticonvulsant therapy.
Adverse effects include changes in behavior, depression, and acute fatal hepatic necrosis in cats.

Midazolam

It uses are the same as diazepam.
It's used for anticonvulsant status epilepticus, but has a shorter elimination time than diazepam (77 minutes vs ~3 hours) for dogs.
It readily crosses BBB.
Adverse effects include mild respiratory depression, vomiting, restlessness, agitation, and local irritation.

Clonazepam

Uses are similar to diazepam, but has limited value as a maintenance anticonvulsant due to rapid tolerance development in dogs.
Adverse effects can include GI disturbances such as vomiting, hyper-salivation, and diarrhea/constipation.

Lorazepam

Its mechanism of action involves activating GABA-gated Cl- channels to potentiate opening activity and evoke neuronal hyperpolarization.
It's useful for seizure control in cats via oral administration.
It's used IV to control status epilepticus, and cluster seizures in dogs, and as a maintenance anticonvulsant as it has a short half life (2-4 hours).

Valproic acid and sodium valproate

Valproic acid is a carboxylic acid derivative.
An effective anticonvulsant in dogs when given orally; however, its short half-life makes long-term use impractical.
It may be useful as an adjunctive treatment in some dogs.
Not evaluated for cats.
Adverse effects include Gl disturbances, hepatotoxicity, CNS effects, dermatologic effects, hematologic effects, pancreatitis, and edema.

Gabapentin

Gabapentin is a synthetic GABA analog that can cross the BBB.
It's mechanism of action involves increasing GABA content in neurons, and inhibiting voltage-dependent Ca2+ channels, decreasing neuronal Ca2+ levels, and inhibiting excitatory neurotransmitter release.
It's helpful as adjunctive therapy for refractory or complex partial seizures, and treating chronic pain in dogs and cats.
It's administered orally.
Adverse effects include sedation, ataxia, and mild polyphagia.

Levetiracetam

It's used orally for adjunctive therapy in refractory canine epilepsy.
It inhibits hypersynchronization of epileptiform burst firing and propagation of seizure activity.
It binds to synaptic vesicle protein 2A in the neuron.
Adverse effects include little side-effects, including changes in behavior, drowsiness, and GI disturbances.

Felbamate

It's a dicarbamate and used in dogs to treat refractory epilepsy.
Not usually associated with sedation.
Used as an anticonvulsant agent for focal or generalized seizures.
Mechanism of action involves blockade of NMDA receptor-mediated neuronal excitation, potentiation of GABA-mediated neuronal inhibition, and inhibition of voltage-dependent Na+ and Ca2+ channels.
Adverse effects include liver dysfunction, but potentially fatal.

Zonisamide

It's a sulfonamide-based anticonvulsant, administered orally twice daily.
It inhibits voltage-dependent Na+ and Ca2+ channels, inducing hyperpolarization and decreasing Ca2+ influx.
It's used for an adjunctive therapy in dogs with refractory epilepsy.
Cost can be a problem for dog use.

CNS Stimulants (Analeptics) - Doxapram

It's medicine used as a CNS stimulant to arouse animals from inhalant and parenteral anesthesia.
It directly stimulates medullary respiratory centers, and probably via activation of carotid/aortic chemoreceptors.
The depth of anesthesia is reduced, but the effect might be transient.
Not effective for reviving severely depressed neonates.
High doses can cause seizures, hypertension, arrhythmias, and hyperventilation leading to alkalosis.

Tranquilizers, Atratics, Neuroleptics, and Sedatives

These terms are interchangeable in veterinary medicine.
They calm the animal and promote sleep, without necessarily inducing sleep at high doses.
These drugs enable less general anesthetic use.

Phenothiazines

Includes various derivatives such as acepromazine, promethazine, and chlorpromazine.
They affect basal ganglia, hypothalamus, limbic system, brain stem, and reticular activating system in the CNS.
Derivatives include dopamine, a1-adrenergic, and serotonergic receptor blockers.
Pharmacological effects include CNS depression, decreased spontaneous motor activity, hypotension, antiarrhythmic/inotropic effects.

Opioids

Opioid analgesia occurs in the brain, spinal cord, and periphery.
µ-receptor agonists produce profound analgesia.
Duration of opioid analgesia is usually shorter than the elimination half-life.
μ-receptor agonists cause respiratory depression in dogs, increasing arterial CO2 tension and reducing pH.
In dogs, μ-receptor agonist administration can cause panting, triggered by the opioid resetting the dog's hypothalamic temperature control point.
Other adverse effects include changes in heart rate, hypotension, and GI effects like constipation.
Opioids are used as analgesics and pre-anesthetic medications for inducing and maintaining anesthesia, particularly in dogs and cats.

Tramadol

It is a synthetic μ-receptor opiate agonist that inhibits the reuptake of serotonin and norepinephrine.
The analgesic effects of tramadol are contributed to its actions on serotonin and norepinephrine.
It is not a controlled drug in the United States but can have potential for human abuse.
It's used as an analgesic or antitussive, given orally.
It is well tolerated in dogs and cats.

Methadone

It's a synthetic µ agonist alternative to morphine.
It causes less sedation and vomiting than morphine.
It is used IV, IM, and SC for pre-anesthetic or analgesic use.
It is very similar to morphine in adverse effects.

Oxymorphone

Dihydroxy derivative of morphine.
Ten times more potent than morphine in terms of analgesia.
It can cause vomiting and sometimes decreases cardiac output while increasing mean arterial pressure and systemic vascular resistance when administered intravenously to dogs.
Used as an analgesic, pre-anesthetic medication, or in neuroleptanalgesia.

Hydromorphone

Injectable opioid sedative/restraining agent and analgesic that is similar to oxymorphone.
It's less expensive but has a shorter duration of action.

Fentanyl

A potent µ agonist used for inducing anesthesia, controlling post-operative or chronic pain.
It is hard to induce anesthesia with fentanyl alone and requires adjunct drugs such as midazolam, thiopental, or isoflurane.
Transdermal fentanyl patches are used for treating chronic pain.

Alfentanil

Derivative of fentanyl, four times less potent than fentanyl.
It is a μ-receptor agonist.
Used as an analgesic and sedative, particularly for cats or adjunctive anesthesia.

Sufentanil

The fentanyl derivative is 5–10 times more potent than fentanyl for analgesic activity, administered intravenously, intramuscularly, subcutaneously, or epidurally.
Used for adjunctive anesthesia, epidural analgesia, or post-operative analgesia.
Major adverse effect is dose-related CNS and respiratory depression.

Carfentanil

Extremely potent µ agonist, about 10,000 times more potent than morphine.
It's used to immobilize large, exotic animals, including ungulates and large carnivores.
Used with xylazine in wild horses.
High potency and potential for disruption of body temperature regulation (hyperthermia/hypothermia), respiratory distress and CNS depression make a reversing agent crucial.

Butorphanol

It's a partial agonist at µ-receptors and a full agonist at к-receptors.
Its analgesic potency is 4-7 times that of morphine.
It can be used to reverse the effects of other opioids, primarily maintaining analgesia.
It has antitussive and antiemetic effects (in dogs) at lower doses.
It's used to relieve coughs associated with inflammation in the upper respiratory tract.
Adverse effects include sedation, ataxia, anorexia or diarrhea in dogs and cats.

Opioid agonist-antagonists

Bind to µ-, κ-, and δ-receptors without activating them.
Used for analgesia (through µ- or к-receptor activation).
Also reverses respiratory and CNS depression of µ-receptor agonists.
Less readily reversible than pure agonists when overdosed.

Buprenorphine

Has 30 times the analgesic potency of morphine.
A partial agonist at µ-receptors and an antagonist at к-receptors.
It's resistant to antagonism by naloxone due to strong µ-receptor affinity.
Used for analgesia in small animals.
Major adverse effects are respiratory depression and sedation. Nalbuphine

Nalbuphine

Equal potency to morphine.
Antagonist at µ-receptors and an agonist at к-receptors.
Used for mild to moderate pain control, with analgesic effects lasting 45 minutes in dogs and 2-3 hours in cats, and topical application for corneal ulcer issues.
Adverse effects are similar to morphine.

Naloxone

High affinity for µ-receptors, lower affinity for к- and δ-receptors, allowing displacement of opioid agonists.
Used for reversing respiratory depression induced by μ-receptor opioids post-operatively.
Also helpful for opioid-induced respiratory depression in newborns.
Useful in treatment of shock.
Naloxone is relatively free of adverse effects.

Naltrexone

Long-acting opioid receptor antagonist for µ-, κ-, and δ receptors.
Used intravenously or intramuscularly for reversing opioid-induced immobilization/depression.
Orally used in cases of behavioral problems.
Usually adverse effects free.

Anxiolytics

No specific information detailed on this topic.

Antidepressants

No specific information detailed on this topic.

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Test your knowledge on the properties of drugs that affect the central nervous system. This quiz covers the blood-brain barrier, neurotransmitters, and the role of second messengers. Challenge yourself with questions on how inflammation impacts drug permeability and the common effects of CNS-active drugs.