Page 660 - Cote clinical veterinary advisor dogs and cats 4th

Epilepsy, Idiopathic 303

Mild, transient side effects (hyperactiv- propranolol, and metronidazole. Other • Target range: 1-2 mg/mL (100-200 mg/dL;
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ity, ataxia) depressants and chloramphenicol can increase 1000-2000 mcg/mL) when used concur-
VetBooks.ir ■ Initial dose: 20-30 mg/kg PO q 24h • Bromide: higher chloride intake increases (200-300 mg/dL; 2000-3000 mcg/mL) when Diseases and Disorders
○ Potassium bromide
the effect of phenobarbital.
rently with phenobarbital and 2-3 mg/mL
used as monotherapy
with food (dog), subsequently changed
bromide elimination, which increases the
based on clinical effects and therapeutic
monitoring dosage requirement; lower chloride decreases PROGNOSIS & OUTCOME
bromide elimination.
Cats: do not use because of substantial
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risk of pneumonitis Possible Complications • About 70% of dogs with idiopathic epilepsy
Steady-state serum concentrations • Phenobarbital-induced hepatotoxicosis can be adequately treated with phenobarbital
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are reached 2-3 months after starting ○ Minimized by avoiding serum concentra- and/or bromide and enjoy a good quality of
therapy or changing the dose. tions > 35 mcg/mL life.
For more rapid control of seizures in ○ Evidence of hepatotoxicosis: increases in • In general, dogs with idiopathic epilepsy have
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dogs with frequent, severe seizures, bile acid concentrations; proportionally a normal life span. However, some dogs with
administer a loading dose of 50-66 mg/ larger increases of alanine aminotransferase recurrent episodes of status epilepticus requir-
kg PO q 6-8h × 48 hours. (ALT) compared to alkaline phosphatase ing emergency treatment have a decreased
Common side effects are polyuria/ (ALP); icterus, weight loss, ascites if very expected life span (≈8 years vs. ≈11 years).
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polyphagia, sedation, and ataxia. severe and advanced
• If seizures are not adequately controlled ○ Potentially reversible if phenobarbital is PEARLS & CONSIDERATIONS
despite target serum concentrations of the stopped early enough
first drug, add a second drug while continu- ○ Elevations in ALP and, to a lesser degree, Comments
ing the first drug. If the seizures become well ALT are common in dogs taking pheno- • A common cause of poor seizure control is
controlled, it may be possible to gradually barbital and do not indicate or predict failure to reach target serum concentrations
wean the first drug. clinically significant liver disease or the before switching to a second drug.
• Other drugs to consider for add-on therapy need to withdraw the drug. • Referral to a neurologist is considered if the
when seizures are not controlled with initial • Phenobarbital rarely causes hematologic diagnosis is uncertain or the seizures are not
drug abnormalities, including neutropenia, anemia, adequately controlled within 3 months.
○ Gabapentin 100-300 mg/dose PO q 8h and thrombocytopenia; the drug must be
(dog, cat) stopped if these abnormalities occur. Prevention
○ Felbamate 15-45 mg/kg PO q 8h (dog) • Bromide increases the risk of pancreatitis • Animals with idiopathic epilepsy should not
○ Pregabalin 2-4 mg/kg PO, q 12h (dog). and may be associated with megaesophagus. be bred because of potential genetic factors.
Start at low end of dose to minimize • Females should be spayed because estrus
sedation. Recommended Monitoring tends to increase seizures.
○ Topiramate 5-10 mg/kg PO q 8-12h Phenobarbital (p. 1372):
(dog). Start at low end of dose to minimize • Measure serum concentrations 14 days Technician Tips
side effects (sedation and ataxia). after starting therapy or changing dose, Have clients bring all medications to their pet’s
• A ketogenic medium-chain triglyceride diet when seizures are not adequately controlled, appointment to check dosages and compliance.
can improve seizure control in dogs already when signs of dose-related toxicosis occur,
being treated with antiseizure drugs. and every 6-12 months. Client Education
• For dogs that suffer clusters of multiple • Blood sample is obtained immediately before Client education is vital. The client must
seizures despite daily medication, at-home the next dose is due (trough serum level), understand the goal of treatment, potential
administration of diazepam per rectum can 8-12 hours after preceding dose was given. side effects, and need for periodic monitoring
decrease the need for emergency veterinary • Blood should not be drawn into serum and dose adjustment. The client must agree
care. The client administers 2 mg/kg of separator tubes because the separator mate- that the benefits of treatment outweigh the side
parenteral diazepam solution per rectum rial may artifactually reduce phenobarbital effects and must not alter treatment without
using a syringe and urinary catheter or teat concentrations in vitro. consulting the attending veterinarian.
cannula, repeated for a maximum total of • Target range: 20-35 mcg/mL (85-150 mmol/L)
3 doses within 24 hours. Because diazepam Bromide (p. 1319): SUGGESTED READING
adheres to plastic, do not store in a syringe. • Measure serum concentrations 1 month and Thomas WB, et al: Seizures and narcolepsy. In
Diazepam suppositories are not well absorbed 3-4 months after starting therapy or chang- Dewey CW, et al, editors: A practical guide to
in dogs. ing dose, when seizures are not adequately canine and feline neurology, ed 3, Ames, IA, 2016,
controlled, when signs of dose-related toxicity Wiley-Blackwell, pp 249–268.
Drug Interactions occur, and every 6-12 months.
• Phenobarbital increases clearance of leveti- • Because of the drug’s extremely long elimina- AUTHOR: William B. Thomas, DVM, MS, DACVIM
EDITOR: Karen R. Muñana, DVM, MS, DACVIM
racetam and zonisamide and can decrease tion half-life, blood samples need not be
the effect of other drugs, such as chlor- drawn a certain number of hours after
amphenicol, glucocorticoids, doxycycline, dosing.

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