Jd. Harkins et al., Bupivacaine in the horse: relationship of local anaesthetic responses and urinary concentrations of 3-hydroxybupivacaine, J VET PHARM, 22(3), 1999, pp. 181-195
Citations number
13
Categorie Soggetti
Veterinary Medicine/Animal Health
Journal title
JOURNAL OF VETERINARY PHARMACOLOGY AND THERAPEUTICS
Bupivacaine is a potent local anaesthetic used in equine medicine. It is al
so classified as a Class 2 foreign substance by the Association of Racing C
ommissioners International (ARCI). The identification of residues in postra
ce urine samples may cause regulators to impose significant penalties. Ther
efore, an analytical/pharmacological database was developed for this medica
tion. The highest no-effect dose (HNED) for the local anaesthetic effect of
bupivacaine was determined to be 0.25 mg by using an abaxial sesamoid loca
l anaesthetic model. Administration of the HNED of bupivacaine to eight hor
ses yielded a peak urine concentration of apparent bupivacaine of 23.3 ng/m
L 2 h after injection as determined with enzyme-linked immunosorbent assay
(ELISA) screening,
The major metabolite re covered from beta-glucuronidase-treated equine urin
e after dosing with bupivacaine is a hydroxybupivacaine, either 3-hydroxybu
pivacaine, 4-hydroxybupivacaine, or a mixture of the two. To determine whic
h positional isomer occurs in the horse, 4-hydroxybupivacaine was obtained
from Maxxam Analytics, Inc., and 3-hydroxybupivacaine was synthesized, puri
fied, and characterized. Furthermore, a quantitative mass spectrometric met
hod was developed for the metabolite as recovered from horse urine, Followi
ng subcutaneous injection of the HNED of bupivacaine, the concentration of
the hydroxybupivacaine recovered from horse urine reached a peak of 27.4 ng
/mL at 4 h after administration as measured by gas chromatography/mass spec
trometry (GC/MS), It was also unequivocally demonstrated with ion chromatog
raphy that the hydroxybupivacaine metabolite found in horse urine is exclus
ively 3-hydroxybupivacaine and not 4-hydroxybupivacaine.
The mean pH of the 4-h urine samples was 7.21; the mean urine creatinine wa
s 209.5 mg/dL; and the mean urine specific gravity was 1.028. There was no
apparent effect of pH, urine creatinine concentration, or specific gravity
on the concentration of 3-hydroxybupivacaine recovered. The concentration o
f bupivacaine or its metabolites after administration of a HNED dose are de
tectable by mass spectrometric techniques, This study also suggests that re
covery of concentrations less than approximate to 30 ng/mL of 3-hydroxybupi
vacaine from postrace urine samples is unlikely to be associated with a rec
ent local anaesthetic effect of bupivacaine.