Barbiturates and benzodiazepines

What is a seizure

Period of altered brain function caused by abnormal electrical activity, leading to unconsciousness, muscle movements, and sensory changes.

Causes of seizures

Trauma, Idiopathic (unknown cause), Infection, Toxin, Metabolic factors

Status epilepticus

Rapid succession of seizures without recovery

Status epilepticus damage to CNS

Elevated body temperature, Hypoxia, Hypoperfusion, Acidosis

Two groups of seizure medication

Drugs to treat status epilepticus and Long term preventative therapy

Characteristics of anticonvulsants

Prevent seizures by suppressing spread of abnormal electric impulses known as CNS depressants

Side effects of anticonvulsants

Ataxia, Drowsiness, Hepatotoxicity

Barbiturates description

Impair transmission of impulses across synapses in the brain

Uses: anticonvulsants and euthanasia solution
• Use as anesthetic agent is limited due to side effects due to Cardiovascular and respiratory depression

Barbiturates

Phenobarbital and Pentobarbital

Phenobarbital

Long acting

controlled substance

Oral tablet/elixir: preventative anticonvulsant of choice in dogs and cats

IV solution: control of status epilepticus

Effects: Induces cytochrome p450 and can increase its own metabolism and metabolism of other drugs

Monitoring: Serum levels of phenobarbital should be monitored regularly to keep drug in therapeutic range

Changes to lab values: Increased liver enzymes frequently seen during therapy

Pentobarbital

Short-acting barbiturate

Controlled substance

IV solution: administered to control status epilepticus

Most commonly used in cases of toxin exposure

Vesicant drug

Also used as a euthanasia solution

Vesicant drug

Very irritating to tissues when administered extravascularly
• Must be careful to administer only into the vein

Bromide (Potassium bromide (KBr)

First-line anticonvulsant

Action: Br competes with chloride ion transport to produce hyperpolarization

Effects: Depresses neurotransmission and Raises seizure threshold and limits spread of seizures

Metabolism: considered liver safe

Half-life: 24 days (Often use loading dose)

Caution: wear gloves when administering

Benzodiazepine description

Function: Potentiate GABA

More GABA effect = reduced action potential generation

Results in reduced neuron excitability: Reduces seizure activity, Muscle relaxation, Reduced anxiety

controlled substances

Benzodiazepines

Diazepam (Valium), Midazolam, Lorazepam

Diazepam

Emergency drug

Intake: IV for status epilepticus, IN or rectal administration

Not used orally: Extensive first-pass metabolism in dogs

Handling: Does not mix well with other medications, Reacts with plastic syringe over time which decreases efficacy

Adverse effects:

• CNS excitement: paradoxical response
• Sedation, weakness
• Idiosyncratic fatal hepatic necrosis: rare effect seen in cats

Midazolam

Intake: IV, IM, or IN for status epilepticus

Compared to diazepam: 3x more potent, Faster onset of action, Shorter duration of action

Adverse effects: Respiratory depression and Agitation and ataxia in horses

Lorazepam

Intake: IN, IM, buccal for status epilepticus may be easier to administer

Metabolism: Not metabolized in the liver

Safer for: patients with liver dysfunction/ obese or geriatric patients

Adverse effects:

• Ataxia
  • Vocalization
  • Increased appetite

Propofol

Short-acting drug

Function: Stimulates GABA

More commonly used as an anesthetic induction agent

Adverse effects: Apnea and Cardiac arrhythmias (Usually seen when given too quickly)