THE BRITISH C H I H U A H U A CLUB
Chihuahua Medical Care
Treatment of 'Killer' for Epilepsy
Mrs Bate-de-Zylva sent us this information to share with you re her dog 'Killer', seven and half year old chihuahua.
Killer was examined on the 30.10.2002 for investigation of a recent onset of epileptic seizures. A first suspected epileptic seizure was observed at the end of August 2002. Ten days later, Killer developed status epilepticus. The last epileptic seizure was witnessed since this status epilepticus. Killer is currently on the following anti-convulsant: Phenobarbitone elixir 0.5 ml (1.5 mg) twice daily and Sodium Valproate 50 mg three times daily as well as Metacam 3 drops once daily and Maxitrol twice daily.
Physical examination: Revealed no abnormality apart from persistent fontanel.
Neurological examination: Revealed normal mental status, posture and gait. Postural reactions were normal on all four limbs. Spinal reflexes were normal on all four limbs. Cranial nerves examination was normal. Cutaneous trunci reflex was normal. No hyperaesthesia could be detected on palpation of the spine.
The history of epileptic seizures suggested a forebrain disorder. Differential diagnosis included (1) primary (idiopathic) epilepsy or (2) secondary epileptic seizures (inflammatory/infectious CNS diseases, brain neoplasm, previous trauma or cerebrovascular accident, malformation or metabolic encephalopathy).
Diagnostic tests: Pre-referral haematology and biochemistry only revealed mildly elevated platelet count (705/mm3).
MRI scan of the brain and CSF analysis were performed on the 30.10.2002. MRI scan of the brain only revealed moderate hydrocephalus and a small quadrigeminal cyst. CSF was collected by lumbar puncture. Results are pending and will be forwarded to you soon.
At this stage, pre-referral blood analysis ruled out metabolic encephalopathy. The only structural abnormality detected on MRI scan of the brain is a moderate hydrocephalus. Pending CSF analysis results should help us to rule out inflammatory/infectious CNS diseases. In case of normal results, the more likely diagnosis would be primary (or idiopathic) epilepsy. The hydrocephalus and quadrigeminal cyst are likely to he congenital considering the breed as well as the persistent fontanel and appear therefore as less likely causes for the epileptic seizures. The diagnosis of primary (or idiopathic) epilepsy is unfortunately a diagnosis of exclusion after elimination of extra-cranial metabolic causes and intra-cranial structural causes. There is no definitive diagnostic test for this condition.
Treatment: The treatment of primary epilepsy is only symptomatic and consists in administration of anti-convulsant medications (Phenobarbitone and/or Bromide). The aim of this symptomatic treatment is to reduce the frequency, intensity and severity of the seizures with acceptable side effects.
As discussed on the telephone, 1 will suggest continuing Killer on Phenobarbitone elixir 0.5 ml, (1.5 mg) twice daily and Sodium Valproate 50 mg three times daily. 1 will also suggest doing serum Phenobarbitone level at the end of this week to ensure that therapeutic serum concentration has been reached. Oral dosage of phenobarbitone will need to be adjusted depending on this serum level. Do not hesitate to contact me if you need any advice doing this oral dosage adjustment. I will finally suggest slowly taking Killer off the valproate acid (over a four to five days period), when serum Phenobarbitone level has been reached.
Phenobarbitone is known to be hepatic enzyme inducer (Cytochrome P450) which means that serum level tends to drop with time.
Therapeutic monitoring of serum drug concentration can be helpful in determining the optimal dose. This is indicated when steady state blood levels are reached after starting treatment (10 to 15 days) or changing dose. This provides a baseline to guide further changes in doses according to clinical circumstances:
- when seizures' frequency increased. This helps to determine the need for dose adjustment before the drug is changed or a second drug added.
- every 3 to 6 months to verify that blood concentration does not drift out of the intended range.
Prognosis: The long-term prognosis of primary (or idiopathic) epilepsy is fair. However, a small number of epileptic dogs may become 'refractory' (high frequency of seizures despite high serum level of anticonvulsant) to Phenobarbitone. Second epileptic drug such as Bromide 30 mg/kg once daily can then be used as an adjunct to Phenobarbitone.
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