Full text of DOI:10.1111/j.1751-0813.2000.tb10350.x

Clinical
2
3. Takahashi Y, Ebihara S, Nakamura Y,
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(Accepted for publication 21 June 1999)
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growth hormone secretion in dogs: effects of 3,6,
and 12 hours of forced wakefulness on plasma
growth hormone, cortisol and sleep stages.
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2
4. Kemppainen RJ, Sartin JL. Evidence for
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Effects of phenobarbitone on serum biochemical tests
in dogs
SF FOSTER, DB CHURCH and ADJ WATSON
Department of Veterinary Clinical Sciences, The University of Sydney, New South Wales 2006
Objectives To investigate effects of phenobarbitone on serum activities of alanine aminotransferase, alkaline
phosphatase and gamma-glutamyl transferase and concentrations of bilirubin, albumin, cholesterol and total protein
in dogs.
Animals
Ten crossbreed experimental dogs and 10 client-owned dogs of mixed breeds treated chronically with
phenobarbitone to control seizures.
Procedures Experimental dogs were allocated to treatment (6 mg/kg oral phenobarbitone, n = 6) and control (no
treatment, n = 4) groups in which serum biochemical tests were performed at intervals during a 3-month period.
Biochemical tests were performed once on the 10 epileptic dogs.
Results
Phenobarbitone caused increased serum alkaline phosphatase activity but did not affect gamma-
glutamyl transferase activity or bilirubin, cholesterol, albumin and total protein concentrations. Phenobarbitone had
minimal effect on alanine aminotransferase activity.
Conclusions
Individual dogs treated with phenobarbitone may have small increases in serum alanine amino-
transferase activity and variable increases in alkaline phosphatase activity but are unlikely to have alterations in
gamma-glutamyl transferase activity or bilirubin, cholesterol, albumin or total protein concentrations.
Aust Vet J 2000;78:23-26
Key words: Dog, phenobarbitone, alanine aminotransferase, alkaline phosphatase, gamma-glutamyl transferase, hypertriglyceridaemia.
ALP
ALT
Alkaline phosphatase
Alanine aminotransferase
GGT
TP
Gamma-glutamyl transferase
Total protein
have, until recently,11 been based on a
study using only two dogs and effects
on GGT have not been investigated.
been reported and these changes have
been attributed to drug-induced enzyme
synthesis and low-grade hepatocellular
injury, with larger increases possibly
associated with morphologic evidence of
henobarbitone and primidone are
the most effective drugs for long
term anticonvulsant therapy in
9
P
1
,2
dogs. As there is a greater potential for
behavioural side-effects and hepatotoxi-
city with primidone, phenobarbitone is
widely regarded as the drug of choice for
Materials and methods
Animals
4
,5
liver injury. Most of the information
about effects of anticonvulsants on the
liver has been based on data for primi-
Dogs from a study of the effects of
phenobarbitone on adrenocortical func-
chronic therapy.1 However, phenobar-
,2
6
-8
done and anticonvulsant combinations
or on studies with few dogs receiving
14
bitone has also been reported to cause
tion tests were used in this study.
3
hepatotoxicosis in dogs.
There were 10 experimental dogs (6
dosed with phenobarbitone, 4 controls)
and 10 client-owned epileptic dogs
(numbered 1 to 10) receiving phenobar-
9
-11
l
a
rge doses of phenobarbitone.
Anticonvulsants may affect results of
laboratory tests commonly used to assess
hepatic abnormalities. Increased serum
activities of ALT, ALP and GGT have
Evidence exists for phenobarbitone-
1
0-13
induced increases in ALP activity
but effects of phenobarbitone on ALT
bitone
to
prevent
seizures.
Aust Vet J Vol 78, No 1, January 2000
23

Clinical
Phenobarbitone-treated experimental
dogs were given 6 mg/kg (5.9 to 6.4
mg/kg) for 12 weeks. The epileptic dogs
had been treated for 14 to 92 months
with 3.9 to 14.4 mg/kg oral phenobarbi-
tone, divided into two or three daily
doses. Four of the dogs (1, 2, 3 and 10)
also received potassium bromide
hypertriglyceridaemia. Both had very
high ALP activities skewing the mean
and there was concern that other
analytes might be similarly affected as
samples had not been cleared of lipid
prior to analysis. Repeatability of
biochemistry results for these two dogs
was very poor, a finding attributed to
lipaemia.
treated dogs, there is little data on ALT:
in one study two dogs were given a rela-
tively large dose of phenobarbitone
9
(13.2 mg/kg daily for 30 d) and in two
others, effects of phenobarbitone in
combination with primidone or pheny-
7
,18
toin were reported.
The most comprehensive study 11
involved measurement of ALT, ALP, TP,
albumin and cholesterol in five epileptic
dogs treated with phenobarbitone for 1
year. Phenobarbitone doses were not
reported but were possibly large because
mean phenobarbitone concentration at
52 weeks exceeded 150 µmol/L. High
liver enzyme activity and abnormal liver
function may occur when serum pheno-
barbitone concentrations chronically
(
Epibrom, Equisci International).
Potassium bromide was considered an
unimportant variable in this experiment
as it is not reported to affect the tested
biochemical variables in dogs or humans
and does not affect drug - metabolising
enzymes in the liver.15-17
Results
Serum phenobarbitone concentrations
in experimental dogs did not change
over time. The means for weeks 6, 8, 10
and 14 were lower than the laboratory’s
suggested therapeutic range of 65 to 194
µmol/L (Table 1). Treatment did not
affect any of the biochemical analytes.
Serum phenobarbitone concentrations
in the epileptic dogs were 72 to 171
µmol/L (mean 110), all within the
suggested therapeutic range. Pheno-
barbitone doses, concentrations, treat-
ment durations and biochemical find-
ings for these dogs are listed in Table 2.
The only mean value outside the refer-
ence range was ALP activity (186 IU/L).
Individuals other than the two excluded
did have mild increases in ALT activity
but no results were sufficiently increased
to cause concern in a clinical setting.
Details of housing, feeding and
husbandry for the experimental dogs are
1
4
given elsewhere. Blood for serum
phenobarbitone concentration measure-
ments was collected at 0900 h on day 5
of weeks 1, 2, 4, 6 (7 for one of the
dogs), 8, 10, 12 and 14. Blood for
biochemical tests (ALT, ALP, GGT,
bilirubin, albumin, TP and cholesterol)
was collected at 0900 h on day 5 of
weeks 1, 2, 4, 6 (7 for one of the dogs),
1
9
exceed 150 µmol/L and this concen-
tration has been suggested as the
maximum acceptable to avoid pheno-
3
barbitone-induced hepatotoxicosis.
Biochemical changes identified in the
study (increased ALT and ALP activities
with decreased albumin and cholesterol
concentrations) were suggestive of hepa-
totoxicosis and chronic fibrosis with
nodular regeneration was found in one
dog that died from unrelated causes.
Thus, the changes observed in ALT
activity may have reflected hepatocel-
lular damage rather than liver enzyme
induction.
In the six experimental dogs treated
here, the overall mean serum phenobarbi-
tone concentration was 63 ± 15 µmol/L
and ALT activity was unchanged. One
dog had a pre-existing mild increase in
ALT activity that did not change during
treatment. Three of the epileptic dogs
had ALT activities above the reference
1
0 and 14. On day 7 of the same weeks,
dogs were administered 0.01 mg/kg
dexamethasone sodium phosphate
(
Dexadreson, Intervet) intravenously to
test low-dose dexamethasone suppres-
1
4
sion.
The epileptic dogs were fasted from
200 h until testing the following
2
Discussion
morning at 0830 h. All dogs were exam-
ined and weighed before having blood
taken at 0900 h for biochemical tests
Anticonvulsants are commonly
reported to cause increased serum ALT
and ALP activities, generally attributed
to enzyme induction and low-grade
(
ALT, ALP, GGT, bilirubin, TP and
4
,5
albumin) and measurement of serum
phenobarbitone and plasma cortisol
concentrations. The dogs were then
given 0.01 mg/kg dexamethasone
sodium phosphate (as for the experi-
mental dogs) and their morning dose of
phenobarbitone.
Biochemical and phenobarbitone
assays were performed by a commercial
laboratory (Macquarie Vetnostics).
hepatocellular damage.
Although
there is experimental evidence that ALP
activity may increase in phenobarbitone-
Table 1. Biochemical test result means for experimental dogs treated with phenobarbitone and
untreated controls.
Weeks
1, 2a
4, 6, 10, 14b
Treated
Analyte
Treated
Control
Control
Analysis of data
ALT (IU/L)
60, 47
58, 51
5, 4
46, 36
70, 69
3, 2
47, 44, 54, 53
48, 58, 44, 46
4, 3, 4, 5
38, 42, 45, 46
54, 49, 37, 44
3, 2, 3, 3
Each serum analyte for the experi-
mental dogs was subjected to a one-way
analysis of variance with repeated
measures design. Statistical significance
was accepted at the 5% level.
Data from the 10 epileptic dogs were
compared with laboratory reference
ranges. Data from two of the dogs (9
and 10) were excluded from calculations
of means and considered separately
because they had unexplained and severe
ALP (IU/L)
GGT (IU/L)
Bilirubin (µmol/L)
TP (g/L)
2, 3
1, 2
2, 2, 3, 2
2, 2, 3, 3
63, 60
34, 32
6, 6
63, 63
32, 31
7, 7
59, 58, 60, 60
31, 29, 31, 31
6, 7, 7, 7
61, 63, 65, 63
30, 31, 31, 32
7, 8, 8, 7
Albumin (g/L)
Cholesterol (µmol/L)
Phenobarbitone (µmol/L)
0, 0
0, 0
72, 56, 61, 59
0, 0, 0, 0
a
b
Values obtained before treatment (weeks 1, 2)
Values obtained during phenobarbitone administration (weeks 4, 6, 10, 14)
2
4
Aust Vet J Vol 78, No 1, January 2000

Clinical
Table 2. Biochemical findings and treatment data for 10 epileptic dogs treated with phenobarbitone (PB).
Variable
Reference
range
Dog
1
2
3
4
5
6
7
8
9
10
ALT (IU/L)
1-70
1-120
0-5
77
241
8
49
345
3
36
386
2
21
150
0
28
43
8
152
128
3
49
102
5
16
94
8
131
8098
12
69
2112
36
ALP (IU/L)
GGT (IU/L)
Bilirubin (µmol/L)
TP (g/L)
0-10
2
9
6
7
7
5
2
3
13
27
53-75
22-36
62
28
9.3
135
92
68
36
7.9
86
65
61
70
35
3.9
102
15
60
30
5.0
101
15
65
30
10.2
99
50
60
30
6.0
72
16
60
18
9.4
89
18
74
78
Albumin (g/L)
PB dose (mg/kg)
Serum PB (µmol/L)
Treatment timea
24
39
39
14.4
171
35
13.8
119
32
5.6
127
14
65-194
a
Treatment time in months
limit (dogs 1, 6 and 9). The increases in
dogs 1 and 6 may have been due to
phenobarbitone or individual variation.
Dog 9 had hypertriglyceridaemia which
can artificially increase ALT activity.20,21
As the epileptic dogs were on various
doses of phenobarbitone, with serum
phenobarbitone concentrations of 72 to
received relatively small doses of pheno-
barbitone and failure of mean serum
phenobarbitone concentrations to reach
suggested therapeutic concentrations
except at week 4 and 12 might explain
the absence of ALP induction.
Alternatively, it may be that more time is
required for induction.
or cholesterol concentrations. The only
abnormal result was the low albumin
concentration of dog 8 (18 g/L) which
was within the reference range (29 g/L)
when retested 1 month later and subse-
quently. Changes to TP and albumin
1
1
reported previously are likely to reflect
hepatotoxic effects of phenobarbitone
and are not a normal consequence of
therapy. Bilirubin concentrations were
unaffected by phenobarbitone adminis-
tration. The high bilirubin concentra-
tions in the two hypertriglyceridaemic
dogs can be attributed to the effects of
1
71 µmol/L, it is reasonable to conclude
In the epileptic group, 7 of 10 had
increases in ALP activity which ranged
from mild (up to two -fold) to marked
(66-fold). ALP activity can be increased
that substantial increases in ALT activity
are unlikely in dogs treated with pheno-
barbitone at usual dose rates. Greater
than two- to three- fold increases may
indicate hepatocellular damage rather
than drug-induced enzyme changes as
previously reported. Hepatotoxicosis,
warranting investigation by liver func-
tion tests and biopsies, can develop in
dogs with prolonged exposure to pheno-
barbitone. Some dogs with phenobarbi-
tone-induced hepatotoxicosis have
normal bile acid concentrations but
2
0.21
by lipaemia
but not by the magni-
tude observed in the two hypertriglyceri-
daemic dogs (9 and 10). Similar ALP
activities in these two dogs were subse-
quently confirmed on samples cleared of
lipid (unpublished data).
2
0,21
lipaemia;
serum bilirubin concentra-
tion from dog 10 was normal when
analysed after lipid clearing.
The two hypertriglyceridaemic dogs
were interesting as neither dog had
hypertriglyceridaemia prior to treatment
with phenobarbitone. Dog 10 was also
treated with potassium bromide but
only after detection of its hypertriglyc-
eridaemia. In man, hypertriglyceri-
daemia may develop in acute and
chronic hepatitis and in any form of
The effects of phenobarbitone on
GGT have not been reported previously.
There were no changes in the experi-
mental dogs, however, some treated and
control experimental dogs had stable
GGT activities at or above the reference
range, suggesting the reference range
may be too low. Mean GGT activity for
the epileptic dogs was within range but
increases in GGT activities were seen in
five dogs. GGT activities in the hyper-
triglyceridaemic dogs (dogs 9 and 10)
would have been increased artefactually
with the GGT assay used in this laboratory
(D Snow personal communication). The
other three abnormal results were very
mild and were considered to reflect a
problem with the reference range.
Overall it would appear that anything
other than mild increases in GGT
activity should be considered abnormal
in dogs receiving phenobarbitone.
3
abnormal BSP retention. High activi-
ties of ALT in dogs treated with pheno-
barbitone may serve as a marker for
hepatotoxicosis although many more
dogs would need to be examined to
investigate this.
2
3
cholestasis. It is possible that both
dogs had cholestatic liver disease that
increased ALP and triglyceride concen-
trations. Alternatively, idiopathic hyper-
triglyceridaemia may have caused a
hepatopathy: hypertriglyceridaemic dogs
may develop a vacuolated hepatopathy
associated with extreme increases in ALP
and increased serum bile acid concentra-
Phenobarbitone has been shown to
increase serum ALP activity in dogs as a
result of hepatic microsomal induc-
1
0,12
tion.
In the six experimental dogs
there was no effect of phenobarbitone
on ALP and none had activities outside
the reference range. Given that increases
of ALP activity have been noted within
5
tion. The role of phenobarbitone, if
1
2,13
2
weeks of initiating treatment,
lack
any, in the induction of hypertriglyceri-
daemia in these two dogs is unknown.
In conclusion, phenobarbitone causes
variable increases in ALP activities but
has no effect on bilirubin, cholesterol,
of adequate time for induction seems
unlikely, although larger doses of pheno-
barbitone were used previously.
Experimental dogs in the current study
No changes occurred in TP, albumin
Aust Vet J Vol 78, No 1, January 2000
25

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recognised and phenobarbitone discon-
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Acknowledgments
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The senior author was supported by a
Lionel Lonsdale Clinical Fellowship. We
thank Dr David Snow and Macquarie
Vetnostics for all biochemical and
phenobarbitone testing, Dr Chris
Holland for assistance with dog 10 and
the Animal Ethics Committee for
granting permission to home experi-
mental dogs as pets at the end of the
experiment. The study would not have
been possible without the co-operation
of the owners of the 10 epileptic dogs.
163.
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phenobarbital administration on results of serum
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