Published: Journal of Analytical Toxicology, Volume 20, Number 2, March/April 1996, pp. 81-88.
Effects of Sodium Bicarbonate and Sodium Chloride
on the Elimination of Etorphine in Equine Urine
D.R. Lloyd, R.J. Rose, A.M. Duffield, and C.J. Suann
The combination of large doses of sodium bicarbonate and the
potent narcotic, etorphine, has reportedly been given to racehorses in attempts
to improve their performance and also to “mask” the presence of etorphine
in urine samples. The increased urinary output and pH associated with sodium
bicarbonate (approximately 500 g) administration may reduce the urinary concentration
of etorphine, making it more difficult to detect. Our experiment was designed
to examine the effects of this combination. Six Thoroughbred horses were used
in a latin-square design with three horse pairs and three treatments consisting
of the following: etorphine (20 µg), etorphine (20 µg) plus sodium
bicarbonate (1.0 g/kg), and etorphine (20 µg) plus sodium chloride (0.7
g/kg). Sodium chloride was used to distinguish between the urinary alkalinizing
effects of sodium bicarbonate and the diuretic effects associated with the large
electrolyte load. Venous blood and urine samples were collected prior to and
for 24 h post- treatment. Sodium bicarbonate produced a significant metabolic
alkalosis and an increase in urine pH. Both sodium bicarbonate and sodium chloride
produced a profound diuresis. After sodium bicarbonate and sodium chloride treatments,
the urinary concentration of etorphine, measured by radioimmunoassay (RIA),
was reduced and in some cases could not be detected. Extraction of the urine
samples, prior to RIA analysis, increased the sensitivity of the assay and in
most cases gave a positive result. We conclude that the coadministration of
etorphine and sodium bicarbonate or sodium chloride can make the detection of
etorphine more difficult because of the dilutional effects associated with the
administration of a large electrolyte load.
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