Today's Veterinary Practice

MAY-JUN 2014

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| THe CanIne SeIzuRe PaTIenT: FouR IMPoRTanT QueSTIonS Today's Veterinary Practice May/June 2014 34 tvpjournal.com they act on a broader range of mechanisms or synergisti- cally; however, side effects can be additive, and determin- ing which AED is effective is difficult when more than one medication is administered. Generally, I recommend using one AED at a time; therefore, AEDs often need to be switched rather than added. Transition Period. Abrupt cessation or missed doses of AEDs is a common cause of seizure and status epilepticus in humans. This may be of less concern in dogs—only 6% of status epilepticus cases in one study resulted from low AED concentration. 26 Nevertheless, tapering the dose prior to stopping an AED is recommended. Risk of seizure can be further reduced if at least one AED is maintained in the therapeutic range during the transition. See Step-by- Step: Transitioning to Newer Generation AEDs. Rescue Therapy AED therapy—additional or different, oral or parenteral— to control cluster seizures or status epilepticus is called rescue therapy. Rescue plans for epilepsy patients are rec- ommended because, among dogs being treated for IE, a 59% incidence of status epilepticus and higher rates of cluster seizures have been described. 27 Furthermore, a 25% mortality rate among all dogs that present for status epi- lepticus has been reported. 26 Predicting Seizures. Recent EEG evidence suggests sei- zures in dogs are not random events, and that forecasting seizures is possible. 28 Therefore, while therapy can be ini- tiated after a seizure, it can potentially be administered before a seizure, as many owners feel they can predict when seizures will occur. Oral Therapy. Oral rescue therapy is appropriate if time to next seizure is an hour or greater, allowing for gastrointestinal absorption and development of useful serum concentration. For example, levetiracetam takes about 81 minutes to reach maximal serum concentration following oral administration. 29 Table 3. aeD Maintenance Therapy in Dogs (Side effect Scale: 1 = Relatively Mild; 5 = Relatively Severe) DRUG DOSE SIDE EFFECT SCALE PRIMARY SIDE EFFECTS REPORTED TOXICITY/DYSFUNCTION Levetiracetam* 20–50 mg/kg Po Q 8 H (or Q 12 H for extended release) 1 ataxia, sedation none Zonisamide* 5–10 mg/kg Po Q 12 H 2 ataxia, decreased eating, sedation affects liver and kidneys Causes urinary calculi Gabapentin 10–30 mg/kg Po Q 8 H 2 Sedation none Pregabalin 2–4 mg/kg Po Q 12 H 2 Sedation none Phenobarbital* 2–6 mg/kg Po Q 12 H 4 ataxia, polydipsia, polyphagia, polyuria, sedation, weakness affects liver, bone marrow, skin, and endocrine system Bromide* 25–50 mg/kg Po Q 8 H 5 ataxia, diarrhea, polydipsia, polyphagia, polyuria, sedation, vomiting, weakness affects esophagus and pancreas Causes gastritis and panniculitis Felbamate 10–40 mg/kg Po Q 8 H 1 Tremors (rare) affects liver and bone marrow Causes keratoconjunctivitis sicca Topiramate 5–10 mg/kg Po Q 8–12 H 1 Sedation May cause urinary calculi Clorazepate 0.05–2 mg/kg Po Q 12 H 3 ataxia, polyphagia, sedation, weakness none * Serum drug monitoring recommended STEP-BY-STEP: TRANSITIONING TO NEWER GENERATION AEDS 1. For 1 week, add a new aeD to the patient's cur- rent regimen. 2. For the next 5 days, reduce the dose of the former aeD by 50%. 3. For the next 5 days, reduce the frequency of the former aeD to once a day. 4. Discontinue administration of the former aeD. • If marked sedation, ataxia, or weakness are noted with the new aeD, more rapid tapering or discontinuation of the former aeD is advised. • If marked increase in seizure frequency is noted in the following weeks to months, a return to the former aeD or addition/substitution of a new, different aeD is recommended. TVP_2014-0506_Seizure Patient.indd 34 5/24/2014 10:44:52 AM

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