Anticonvulsants Flashcards
Seizure (convulsion)
Clinical manifestation of abnormal activity in the brain
Epilepsy
Multiple seizures over a long period of time
Status epilepticus
Seizure lasting at least 5 minutes or 2+ discrete seizures without full recovery of consciousness between seizures
Primary cause of seizures
Idiopathic epilepsy
Secondary cause of seizures
Distemper, head injury, encephalitis
Reactive cause of seizures
Fever/heatstroke, poisoning
At home treatment of seizures
Diazepam 1-2mg/kg via rectum up to 3x/24hrs
In hospital treatment of seizures
Diazepam 5-10mg IV to effect
Diazepam 1-2mg/kg rectal if no IV access
0.5mg/kg/hr CRI if seizures reoccur after Diazepam bolus
Lorazepam, Midazolam, Clonazepam, Chlorazepate
Phenobarbital (10-20mg/kg IV increments to effect)
If no response - general anesthesia
When do you start treatment when diagnosed with epilepsy?
More than 1 seizure per month, seizure within 1 week of head injury, or when brain lesion is ID’s
Drugs to avoid
Phenothiazines
Butyrophenones
Opioid agonists
Fluoroquinolones (+NSAIDs) - lower seizure threshold
Where do Benzodiazepines act?
GABA agonist
Where does Phenobarbital act?
GABA agonist
Where does Gabapentin act?
Block Ca2+ channels
Where does Felbamate act?
GABA agonist
NMDA antagonist
Block Na+ channels
Where does Valproate act?
GABA agonist
Block Ca2+ channels
Clinical uses for Benzodiazepines
Emergency anticonvulsant
Clinical uses for Phenobarbital
Initial therapy (drug of choice in cats and dogs)
Clinical uses for Bromide
Add-on to Phenobarbital or initial therapy
Clinical uses for Levetiracetam
Mono therapy or as an add-on to Phenobarbital
Clinical uses for Valproate
Add-on to Phenobarbital
Clinical uses for Zonisamide
Add-on to Phenobarbital or mono therapy
Clinical uses for Gabapentin
Add-on with Phenobarbital and/or Bromide
Clinical uses for Felbamate
Add-on to Phenobarbital or mono therapy
Side effects of Benzodiazepines
Enzyme induction (will effect PK of other drugs)
Side effects of Phenobarbital
Sedation
Hyperexcitability
Prolonged use/high dose = hepatotoxic - cytochrome P450 induction
Side effects of Bromide
Sedation
Emesis
Pancreatitis
Side effects of Levetiracetam
Sedation
Polyphagia (uncommon)
Side effects of Zonisamide
Sedation
Emesis
Cytochrome P450 induction
Side effects of Gabapentin
Sedation
Mild ataxia
Side effects of Felbamate
Nervousness
Hepatic disease?
Side effects of Valproate
Alopecia
Hepatotoxicity
Emesis (give with food)
Contraindications of Benzodiazepines
Diazepam PO in cats = FATAL LIVER NECROSIS
Contraindications of Phenobarbital
Liver disease
Contraindications of Bromide
Cats - pneumonitis
Hyperadrenocorticism (NaBr)
Congestive heart failure (KBr)
Contraindications of Gabapentin
Oral solution has Xylitol - TOXIC to dogs = pancreatitis
Special considerations for Benzodiazepines
Diazepam is most common
Not for long-term Tx
Short duration = frequent administration
Cross-tolerance
Special considerations for Phenobarbital
LONG DURATION
IV loading dose
Metabolized in liver
Half-life decreases after 4 days (100->24hrs)
Special considerations for Bromide
KBr with congestive heart failure
Loading dose, add NaBr if IV
T1/2 = 21-24 days
Special considerations for Levetiracetam
Not metabolized (excreted unchanged) T1/2 = 3-4hrs (dogs), 3hrs (cats)
Special considerations for Zonisamide
Liver induction
T1/2 = 15hrs (dogs), 35hrs (cats)
Special considerations for Gabapentin
Partially metabolized in the liver
T1/2 = 2-4hrs (dogs)
Special considerations for Felbamate
30% metabolized in the liver
T1/2 = 5-6hrs (dogs)
Special considerations for Valproate
T1/2 = 1.5-3hrs (dogs), 8.5hrs (cats)
