Here is a small selection of some of the data generated by the monitoring scheme.

Breeds reported:

Results expressed as a percentage of forms that had a reply for this question.


It can be seen that four main breeds make up over one third (36%) of all reported; German Shepherd, Labrador, Border Collie and Golden Retriever. Overall seventy-six pure breeds were recorded ranging from Dachshunds to Great Danes. The weight distribution coincided with this with the 21 – 30 kg range being the most common (32.3%).

Sex and Neuter Status:

Expressed as a percentage of forms that had a reply for this question.


Reason for serum sampling:

Expressed as a percentage of forms that had a reply for this question.


Overall 43% of the dogs that were serum tested were categorised as being controlled/ routine with the remaining dogs almost equally divided between the other categories. The category ‘other’ included a lot of dogs that had just commenced phenobarbital therapy.

Frequency of Seizures in ‘controlled’ group:

Expressed as a percentage of forms that had a reply for this question:


The group of dogs classed as being controlled, were evenly divided into each seizure frequency category. At either end of the scale, 15% of dogs had a seizure episode every 0 – 2 weeks, while 32% experienced a seizure frequency of 3 months or more. This illustrates the wide variations in opinion as to what constitutes good control of seizures.

Dose of Epiphen in mg/kg for controlled dogs:

Expressed as a percentage of forms that had a reply for this question.


It can be seen from the graph that more than half (50.9%) of dogs reported as having their seizures controlled are receiving between 2.5 – 5.0 mg/kg phenobarbital, although more than one-third are receiving a larger dose (20.4%, 5.0 – 7.5mg/kg, 8.8%, 7.5-10 mg/kg and 10.2% over 10mg/kg). A small group of dogs with controlled seizures (9.7%) are receiving 0 – 2.5 mg/kg phenobarbital.

Effects of dose on serum concentrations


In dogs receiving oral doses of phenobarbital >10mg/kg there was a significant difference between ‘trough’ (up to 2 hours before dose due) and ‘non-trough’ serum phenobarbital concentrations. This effect was not significant in dogs receiving doses <10mg/kg. This finding means that ‘trough’ blood samples are not essential for dogs receiving lower doses of phenobarbital. In dogs receiving doses >10mg/kg it is important to be consistent in the timing of blood sampling relative to dose times so that sequential samples can be compared.

Published data

Information from records from the blood analysis of over 1400 dogs receiving chronic phenobarbital therapy and collected under the serum monitoring scheme were studied. The dogs were divided into 2 groups


1. dogs where samples were collected when phenobarbital levels were predicted to be at the lowest (ie blood samples collected within 2 hours of next dose being due (trough sample))


2. dogs where samples collected when phenobarbital levels predicted to be above trough levels ie (collected at other times between phenobarbital doses).


There were 918 dogs in group 1 and 509 in group 2. No significant difference was found in phenobarbital levels in dogs I the trough and non-trough groups. However when dogs were receiving higher doses of phenobarbital (and particularly in those receiving more than 10mg/kg phenobarbital daily) there was more difference between trough and non-trough blood levels of phenobarbital. This finding means that it may not be necessary to collect ‘trough’ samples when monitoring all dogs receiving phenobarbital – however collection of a trough sample is likely to be more important on dogs receiving large daily doses of the drug if an accurate measure of serum concentrations is to be achieved.








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