Anticonvulsants Flashcards
what is a seizure
sudden intense electrical discharge in the thalamocortex
what is a convulsion
generalized tonic-clonic seizure that may or may not be associated with epilepsy
what is tonic-clonic?
Tonus: increased mm tone
Clonus: alternating rapid contraction and relaxation
what is status epilepticus
a series of seizures in rapid succession with no intervening periods of consciousness, lasting 30+ minutes
what is epilepsy and what are its 3 characteristics
Recurrent, spontaneous impairment of brain function
- loss of consciousness
- abnormal motor function
- mental or sensory disturbances
what is the difference between a focal and generalized seizure
focal: usually unilateral involvement of the cerebrum, minor abnormalities
generalized: usually bilateral involvement of the cerebrum, loss of consciousness, tonic-clonic motor activity
what is the goal of anticonvulsant therapy
reduce the frequency and severity of seizures, not abolish
what are the most common drugs used to PREVENT seizure
- phenobarbital
- KBr
- levetiracetam
- gabapentin
what is the most common drug used to STOP seizures
diazepam
why cant we use diazepam for long-term control of seizures
tolerance develops within 1-2 months
why is diazepam not a good treatment for seizures in cats
hepatic toxicity likely
why do we use so few anticonvulsant drugs in animals when so many exist in humans
1) metabolized very differently in dogs and cats (numerous daily doses)
2) different adverse effects
3) cost
T/F combination therapy for anticonvulsants is very common
T
what is the #1 anticonvulsant in small animals
Phenobarbital
what type of drug is phenobarbital
barbiturate with anticonvulsant activity at low concentration
how does phenobarbital prevent seizures
facilitates GABA (hyperpolarizes cells)
what is phenobarbital half life in:
- dogs
- cats
dogs: 20-140, ~48h
cats: <48h
in dogs, the half-life decreases with duration of therapy due to induction of p450 enzymes so you have to increase dose gradually throughout life
what do you do if you have been treating a dog with phenobarbital for long enough that you are reading toxic doses
add an adjunct therapy or switch to KBr
what are the advantages of phenobarbital as an anticonvulsant (4)
1) inexpensive
2) q12 administration
3) best outcomes of any monotherapy for dog/cat epilepsy
4) effective in many species
what are the main disadvantages of phenobarbital as an anticonvulsant (4)
- sedation (can last ~2w)
- PU/PD, V, polyphagia (can persist)
- induces cytochrome p450 in dogs
- potential hepatotoxicity due to drug tolerance
how do we get around the disadvantages of phenobarbital
monitor blood levels
what is a rare possible side effect of KBr phenobarbital therapy (and all other anticonvulsants)
pancreatitis
how should you transition between anticonvulsants
taper blood levels by ~10% every 3 weeks
what is the most common anticonvulsant used in cats
phenobarbital
what anticonvulsant is contraindicated in cats and why
KBr: causes an asthma-like condition in cats which can be fatal
what is the MoA of KBr
hyperpolarizes membranes by flowing through Cl channels in neuron PM
what are the advantages of KBr
- effect can be as good as PB
- no hepatic metabolism (no toxicity, no changes in dose required over time)
- q24 administration
- cheap
what are the man disadvantages of KBr
- sedation and lethargy
- PU/PD/PP/V and V may persist
- cannot use in cats due to pulmonary inflammation
- long half-life means it takes months to titrate to effect
- narrow therapeutic index
T/F KBr is not sold as a pharmaceutical
T -> prepared from industrial powder
what is an important dietary consideration for a patient on KBr
the body treats Cl- and Br- the same, so diets that increase Cl- will increase Br- excretion in the kidney
what is the MoA of levetiracetam
unknown
how is Levetiracetam given
12 daily as an adjunct, commonly with phenobarbital
how do we use gabapentin as an anticonvulsant
q12h treatment in combination with other anticonvulsants
what is the MoA of gabapentin
synthetic analogue of GABA
what are the dangers of using diazepam in cats
- idiosyncratic hepatic necrosis
- hepatic toxicity
how can diazepam be administered
- in clinic
- at home
- in clinic: IV
- at home: per rectum
when and how frequently would diazepam be given by an owner at home (or in hospital)
at first sign of seizure (prodromal sign); repeat at 20 and 40 min
what should you use if diazepam fails to stop a seizure
IV phenobarbital, then try general anesthetics (propofol, inhalant)
why don’t we use the following drugs in animals:
- primidone
- phenytoin
- clonazepam
Primidone: hepatic toxicity worse than PB
Phenytoin: half-life in dogs too short to be useful
Clonazepam: ineffective after 1-2 months
