Barbiturate Pharmacology Quiz

Drugs Acting on the Nervous System

• Drugs acting on the nervous system are categorized to aid in understanding and treatment.
• An unauthorized reproduction and/or distribution of this document is punishable by law.

Divisions of the Nervous System

• Central Nervous System (CNS): Contains the brain and spinal cord;integrates control center.
• Peripheral Nervous System (PNS): Consists of peripheral nerves, cranial, and spinal nerves; communication between the CNS and body.
  • Sensory (Afferent) Division: Composed of sensory neurons; conducts signals from receptors to the CNS.
  • Motor (Efferent) Division: Contains motor neurons; conducts signals from the CNS to effectors (muscles and glands).
    • Autonomic Nervous System: Controls involuntary responses.
      • Sympathetic Division: Mobilizes body systems (flight-or-fight).
      • Parasympathetic Division: Conserves energy (rest-and-digest)
    • Somatic Nervous System: Controls voluntary movement.

CNS Drugs

• Organs: Brain and spinal cord
• Goals: Develop drugs to elucidate and manipulate the normal CNS, to correct pathophysiological changes in abnormal CNS.
• Functions:
  • Anticonvulsive effects
  • Tranquilization
  • Analgesia
  • Anesthesia

CNS Drug Classifications

• Narcotics
• Hypnotics
• Tranquilizers
• Anesthetics
• Neuroleptics
• Analgesics
• CNS Stimulants
• Sedatives
• Dissociatives
• Anticovulsants

Seizures vs. Convulsions

• Seizures: A sudden, uncontrolled electrical disturbance in the brain.
• Convulsions: Specific type of seizure characterized by involuntary muscle contractions. All convulsions are seizures but not all seizures are convulsions.

Anticonvulsants MOA

• Mechanism of Action (MOA): Stabilization of neuronal membranes
  • 1. Hyperpolarization of neuronal membranes through ion channels.
    • Blocks sodium channels.
    • Activates potassium channels.
    • Regulates calcium channels.
  • 2. Hyperpolarization of neuronal membranes through GABA-gated chloride channels.

Anticonvulsants Indications & Adverse Effects

• Indications: Reduce the incidence, severity, or duration of seizures.
• Adverse Effects:
  • Withdrawal symptoms, seizures, status epilepticus can follow rapid cessation or administration with other drugs
  • Lowered seizure threshold when administered with other drugs.
    • Phenothiazines (e.g., Acepromazine).
    • Anthelminthics (e.g., Pyrantel, Levamisole).
    • Metoclopramide.
  • Enzyme induction (Cytochrome P450)
  • Hepatotoxicity

Barbiturates

• Classification: Anticonvulsant
• Subtypes: Phenobarbital, Primidone, Pentobarbital
• Difference in Duration of Action: Ultra-short acting, Short acting, Long acting

Benzodiazepines

• Classification: Anticonvulsants
• Subtypes: Diazepam, Midazolam, Lorazepam, Zolazepam
• Reversal Agent: Flumenazil (competitive antagonist)

Bromides

• Classification: Anticonvulsants
• Subtype: Potassium bromide (KBr)
• MOA: Hyperpolarization of neuronal membranes through chloride channels.
• Not to be used in Cats: Because it can cause severe asthma-like symptoms

Adjuncts

• Levetiracetam
• Zonisamide
• Gabapentin
• Felbamate
• Phenytoin

Phenytoin

• MOA: Sodium influx during action potential, Calcium influx during depolarization, delayed potassium efflux during action potential.
• Unique Characteristics: Not recommended anti-convulsant due to short half-life, Tx/Mgt for digitalis-induced ventricular arrhythmias due to its lidocaine-like effects.

Tranquilizers, Ataractics, Neuroleptics, & Sedatives

• Description: Drugs that calm the animal and promote sleep but do not necessarily induce sleep. Often used as pre-anesthetic medications.

Phenothiazines

• Description: Tranquilizers that block dopamine, α-1, histamine, acetylcholine & serotonergic receptors, leading to a calming effect.
• Pharmacological Effects: Tranquilization, hypotension, and epinephrine reversal.
• Adverse Effects: Respiratory depression, hyperprolactinemia, hyperglycemia, decreased GIT motility, and impaired thermoregulation.
• Extrapyramidal Symptoms: Can cause muscle tremors, rigidity, bradykinesia, dystonia, and dyskinesia.
• Indications: Tranquilization, anti-emetic, pre-anesthetic.
• Contraindications: Epilepsy, hypovolemic/hypotensive patients, liver dysfunction, anti-ChE, poisoning.
• No Reversal Agent Available
• Specific Phenothiazines: Acepromazine, Chlorpromazine, Promazine, Fluphenazine.

Butyrophenone

• Description: Tranquilizers that are more potent than phenothiazines. Block dopamine receptors.
• Pharmacological Effects: Same as phenothiazines, potentially more potent.
• Specific Butyrophenones: Droperidol, Azaperone (often used with fentanyl or other anesthetics in animals).

α-adrenergic Agonists

• MOA: Activate α-2 receptors and α-1 receptors (high doses), decreasing neurotransmitter release.
• Pharmacological Effects: Sedation, analgesia, muscle relaxation, emesis, mild hypertension to hypotension, diuresis, and hypoxemia (in ruminants).
• Specific α-agonists: Xylazine, Detomidine, Medetomidine, Romifidine.
• Important Characteristics & Considerations for use:
  • Xylazine, for example, has a prolonged effect and can be used pre-anesthetically.

Chloral Hydrate

• MOA: Reduced to trichloroethanol in the body; causes CNS depression and sedation.
• Pharmacological Effects: Marked hypnotic effect, and cerebral/respiratory depression as well as poor analgesic capability.
• Indications: Primarily in horses, basal necrosis, and anesthesia.

Opioids

• Description: Drugs that bind to opioid receptors.
• Subtypes: Agonists, antagonists, and partial agonists.
• Opiates: Derived from opium (poppy plant). These are typically opioid agonists.
• Examples of Opioids: Morphine, Tramadol, Methadone, Oxymorphone, Hydromorphone, Fentanyl, Alfentanil, Sufentanil, Carfentanil, Buprenorphine, Nalbuphine, Naloxone, Naltrexone, and Butorphanol.
• Important Considerations: Potency, duration of action, receptor affinity, safety margin.

Anxiolytics/Anti-depressants

• Anxiolytics: Drugs designed to treat anxiety;
• Anti-depressants: Used for depression, anxiety or other mood disorders.
  • Tricyclic Antidepressants (TCAs): Amitriptyline, Clomipramine, Imipramine, Doxepin
  • Serotonin Selective Reuptake Inhibitors (SSRIs): Fluoxetine, Paroxetine, Sertraline, Fluvoxamine
  • Monoamine Oxidase Inhibitors (MAOIs): Selegiline
  • Progestins: Medroxyprogesterone acetate (MPA), Megestrol acetate (MA). Most often progestins are used to treat more complex behavioral or medical conditions.