Page 810 - Problem-Based Feline Medicine

802 PART 10 CAT WITH SIGNS OF NEUROLOGICAL DISEASE

sion (to 0.75–1.0 mg/kg/h), or give a pheno-
● Measure serum benzodiazepine concentration at
barbital IV bolus (2–5 mg/kg) and add pheno-
steady state (reached within 4–5 days) and adjust
barbital to the diazepam infusion (0.5–1
the dosage to obtain at least 500–700 nmol/L
mg/kg/h) for at least 4–6 hours before attempt-
(ng/L); use the same formula as for phenobarbital.
ing to decrease it. Because it takes at least 20
– Also measure liver enzymes to detect rare idio-
minutes for a phenobarbital IV bolus to exert its
syncratic acute hepatic necrosis induced by
anticonvulsant effect, sustained seizure activity
diazepam in cats.
must be controlled with diazepam in the mean
● Add gabapentin 10–40 mg/cat q 8 h if seizures are
time.
still not well controlled despite optimal phenobar-
– If phenobarbital is to be started as a mainte-
bital concentrations and benzodiazepine concentra-
nance anti-epileptic drug, a loading dose of
tions.
15–20 mg/kg (slow IV bolus) may be given to
– Potassium bromide (KBr) is contraindicated
immediately achieve a therapeutic serum con-
in cats; in a study of 26 cats treated with KBr,
centration of 60–110 μmol/L (15–25 μg/ml).
42% developed respiratory signs from 7 weeks
Maintenance dosing should be continued after-
to 14 months after onset of therapy. Two cats
wards (2.5 mg/kg q 12 h PO or IM if the cat is
died of their airway disease. The safety of
sedated to the point it is unable to safely swal-
potassium bromide use in the cat remains
low). Phenobarbital is potentiated by diazepam.
a serious issue. If there are no other options,
Close monitoring of the patient must be done
monitoring monthly by way of thoracic radi-
when adding phenobarbital to diazepam.
ographs should be done. The clinical signs
– If the cat is already treated with chronic oral
resolve with the arrest of treatment (up to 17
phenobarbital therapy and its phenobarbital con-
months are required for full recovery).
centration is known to be sub-therapeutic, it can
Anti-epileptic drug therapy is likely to be required for be immediately increased by administering an
life. Only if the cat remains seizure-free for longer than IV bolus; each 1 mg/kg IV bolus will increase
6–12 months should slow weaning from drugs be the phenobarbital concentrations by 5 μmol/L
attempted. Weaning should occur over a few months with (1 μg/ml).
one drug at a time. If more than one seizure/8 weeks ● If seizures are not adequately controlled, propo-
recurs during or after drug withdrawal, resume treatment. fol at sub-anesthetic dosage can be administered.
● Status epilepticus and cluster seizures require Use an IV bolus of 1.0–3.5 mg/kg plus a continuous
emergency treatment. IV infusion of 0.01–0.25 mg/kg/min, to effect, for
– First give a diazepam bolus of 0.5 mg/kg IV. several hours (up to 12–48 hours, if necessary)
Repeat if the seizure has not stopped within 1–2 before attempting weaning.
minutes or if another one begins. ● If high-frequency or sustained convulsive
– Immediately start a diazepam constant rate seizures persist despite the above treatment,
IV infusion of 0.5 mg/kg/h to prevent seizure proceed to general anesthesia with pentobarbital
recurrence. (5–15 mg/kg slow IV over several minutes, to effect;
– Mix the diazepam in an in-line burette with wait 10 minutes to see maximal effect before giving
maintenance fluids. Prepare only 1–2 hour sup- more).
ply at a time as diazepam is rapidly adsorbed – Add an IV continuous rate infusion of 5 mg/kg/h
into the plastic tubing and is inactivated by expo- for at least 6 hours if other seizures occur after-
sure to light. wards.
– When no seizures have occurred after 4–6 hours, – Intubation and ventilation are recommended
slowly decrease the infusion rate (25% steps as well as close anesthetic monitoring (tempera-
every 4–6 hours). ture, blood pressure, etc.).
– If > 2 seizures occur during the diazepam – Isoflurane anesthesia is the last resort for
infusion, either give another diazepam bolus refractory seizures. It should be done for at least
(0.5 mg/kg) and increase the diazepam infu- a few hours.