Mônica Vicky Bahr Arias. Revista Clínica Veterinária, n.81, julho 2009
Resumo: A epilepsia é uma das alterações neurológicas mais frequentes na clínica de pequenos animais. As causas de convulsão no cão e no gato são variadas e o êxito do tratamento das desordens convulsivas se baseia no diagnóstico correto da síndrome neurológica quanto à sua origem idiopática, sintomática ou criptogênica. Aproximadamente 80% dos pacientes epilépticos tratados com anticonvulsivantes ficam livres das crises de forma permanente ou apresentam quadros de menor intensidade e frequência. As causas de falha terapêutica incluem doença progressiva, orientação inadequada do proprietário, seleção indevida de um anticonvulsivante, intolerância aos efeitos do medicamento e epilepsia resistente ao tratamento. Este artigo aborda a avaliação correta do paciente e os princípios da terapia farmacológica, com ênfase na monoterapia, para reduzir as interações e os efeitos colaterais.
Abstract: Epilepsy, one of the most common neurological disorders found in small animal practice, is characterized by the recurrence of seizures. The causes of convulsions in dogs and cats are varied and successful treatment of convulsive disorders depends on correct diagnosis. It is important to determine whether a seizure has occurred and to distinguish it from a syncopal episode, narcolepsy/cataplexy or episodic weakness. Epilepsy classification is based on its underlying etiology, including idiopathic epilepsy, symptomatic epilepsy, and probable symptomatic epilepsy. Seizures may be caused by extracranial and intracranial factors. Reactive epileptic seizures are not true epilepsy and result from an extracranial disease. Intracranial causes include neoplasia, infectious/inflammatory diseases, hydrocephalus, trauma, vascular disease, and primary epilepsy; extracranial causes include metabolic problems and toxicity. Seizure activity in young animals suggests congenital anomalies such as hepatic encephalopathy, infectious diseases, traumatic or metabolic disorders. Animals which are older than five years of age are more likely to have infectious diseases, neoplasia, degenerative diseases, trauma, metabolic disorders and acquired epilepsy. Idiopathic epilepsy may occur at any age, but it occurs most frequently in dogs or cats between six months and five years of age. Although idiopathic epilepsy in cats is an important cause of seizures, brain tumors and inflammatory diseases are more likely to cause seizures. A physical and complete neurological examination is very important in all animals with a seizure disorder. Animals with idiopathic epilepsy are expected to be neurologically normal during the inter-ictal period whereas animals with seizures from toxic, metabolic, congenital, neoplastic, and inflammatorydisorders may have neurological abnormalities between seizures. A description of an animal's seizures, their frequency and duration, and the animal's behavior between seizures may be helpful in determining the cause of a seizure disorder. Data on the environment, the nutritional status, immunizations, previous illnesses or injuries, age at onset of seizures, type and frequency of seizures provide important diagnostic information. A complete blood count, serum chemistry profile, including fasting blood glucose, calcium, BUN, albumin, total protein, cholesterol, triglycerides, urinalysis and radiographs of the thorax or abdomen should all be done for animals that have had one or more seizures. Cerebral spinal fluid analysis, electroencephalography, neuroradiography, and serum titres for infectious diseases may be helpful in determining etiology. The decision to start anti-epileptic drug therapy should be based on each individual case. Use of anti-epileptic drugs is indicated when a diagnosis of primary epilepsy is made, or when treatment of the underlying cause of the seizures in secondary epilepsy does not control seizures. General recommendations for initiating therapy include a single seizure occurring more than once every 4-6 weeks, cluster seizure activity or status epilepticus regardless of frequency. The primary goal of therapy is to balance adequate seizure control with acceptable drug adverse effects. Monotherapy is the initial goal of treating any seizuring dog or cat in order to reduce possible drug interactions and adverse effects. The most common drug used to treat seizures in veterinary medicine is phenobarbital, a relatively inexpensive, well-tolerated drug that can be administered two times per day to prevent seizures in dogs and cats. The appropriate starting dose of phenobarbital for dogs is 2.5 to 5mg/kg orally q12h. It is also the recommended first-line anticonvulsant drug in epileptic cats. Most cats can be treated with 1-2mg/kg/day. Monitoring of serum phenobarbital concentrations is important in the management of epileptic dogs treated with this drug, because seizure control in dogs and cats correlates best with serum phenobarbital concentration, not with the administered dose. The therapeutic range for serum phenobarbital concentration in dogs has been established at 15 to 45µg/mL, although concentrations above 35µg/mL are associated with an increased risk of hepatotoxicity. Dogs treated with phenobarbital should be monitored every 4-12 months with a physical examination, measurement of phenobarbital blood levels and a chemistry panel to check for signs of hepatotoxicity. Potassium bromide is used most commonly as a second anticonvulsant in dogs refractory to phenobarbital alone, or it can be used alone. As it is not metabolized in the liver, it is an ideal anticonvulsant for patients with liver disease. It is not recommended in cats due to the high prevalence of adverse respiratory problems. Diazepam, a very effective anticonvulsant; must be used primarily in emergency situations, due to its short duration of action and the fact that dogs develop tolerance to it. In refractory epileptic canine patients, other new antiepileptic drugs can be added to the standard treatment. However, pharmacokinetics and efficacy of many of these new drugs are not well known. The causes of treatment failure include the presence of progressive disease, inadequate guidance to the owner, inappropriate selection of an anticonvulsant, intolerance to effects of the drug and epilepsy resistant to treatment 4,16. This article discusses the correct assessment of the patient and the principles of pharmacological therapy, with emphasis on monotherapy to reduce interactions and side effects.
Resumen: La epilepsia es uno de los trastornos neurológicos más frecuentes en la clínica de pequeños animales. Las causas de las convulsiones en el perro y el gato son variadas y el éxito o el fracaso del tratamiento de los desórdenes convulsivos se basa en el correcto diagnóstico del síndrome epiléptico, en cuanto a su naturaleza idiopática, sintomática o criptogenética. Aproximadamente 80% de los pacientes epilépticos tratados con anticonvulsivantes quedan libres de crisis en forma permanente o presentan crisis en menor intensidad o frecuencia. Las causas de fallas terapéuticas incluyen la presencia de desórdenes subyacentes, deficiente educación al cliente, inapropiada selección del medicamento, intolerancia a los efectos del medicamento y a ataques que no responden al medicamento. En este artículo se revisan la evaluación adecuada del paciente, los principios de la farmacología antiepiléptica, con énfasis en la monoterapia para reducir las posibles interacciones farmacológicas y los efectos secundarios.
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