The effects of equivalent doses of tromethamine or sodium bicarbonate in healthy horses.
OBJECTIVE
To describe the effects of tromethamine, a putative treatment for metabolic acidosis, and to compare its biochemical effects with those of sodium bicarbonate.


METHODS
Randomized intervention study with repeated measures.


METHODS
16 healthy horses, 3 to 17 years old, weighing 391 to 684 kg.


METHODS
Ten horses received 3 mEq/kg tromethamine and six received 3 mEq/kg sodium bicarbonate. Samples of venous blood and cerebrospinal fluid (CSF) were collected at intervals before and after drug administration. Heart rate and breathing rate were also recorded at intervals.


RESULTS
Median standard base excess increased significantly (P < .05) from baseline immediately after both bicarbonate and tromethamine. These increases were not significantly different between treatments. Standard base excess returned toward baseline but remained significantly increased 3 hours after infusion of either treatment. After tromethamine, there was a significant decrease in plasma sodium concentration that lasted for at least 90 minutes. After sodium bicarbonate, no change in plasma sodium concentration was detected. Both sodium bicarbonate and tromethamine increased carbon dioxide tension in venous blood and CSF. Despite venous alkalemia, the pH of CSF decreased after both treatments.


CONCLUSIONS
Tromethamine and sodium bicarbonate have similar alkalinizing ability. Tromethamine causes hyponatremia, whereas both tromethamine and sodium bicarbonate increase carbon dioxide tension in venous blood and CSF.


CONCLUSIONS
If hyponatremia, hypercarbia, and acidosis of the CSF occur after tromethamine is given to horses with existing metabolic acidosis, some of the potential advantages of tromethamine may prove theoretical rather than practical.
Pedrick
T P
TP
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Moon
P F
PF
Ludders
J W
JW
Erb
H N
HN
Gleed
R D
RD
D000136:Acid-Base Equilibrium / Q000187:drug effects*; D000818:Animals; D001798:Blood Proteins / Q000187:drug effects; D002021:Buffers; D002245:Carbon Dioxide / Q000097:blood / Q000134:cerebrospinal fluid; D002712:Chlorides / Q000097:blood / Q000134:cerebrospinal fluid; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006400:Hematocrit / Q000662:veterinary; D006736:Horses / Q000097:blood* / Q000134:cerebrospinal fluid* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008297:Male; D010100:Oxygen / Q000097:blood / Q000134:cerebrospinal fluid; D012119:Respiration / Q000187:drug effects; D012964:Sodium / Q000097:blood; D017693:Sodium Bicarbonate / Q000494:pharmacology*; D014325:Tromethamine / Q000494:pharmacology*
D001798:Blood Proteins; D002021:Buffers; D002712:Chlorides; D014325:Tromethamine; D002245:Carbon Dioxide; D017693:Sodium Bicarbonate; D012964:Sodium; D010100:Oxygen