Reduction of the red blood cell mass of horses: toxic effect of heparin anticoagulant therapy.

This research article discusses how different doses of heparin, an anticoagulant medication, affects the red blood cells in horses. The study found that larger doses of heparin decrease the number of red blood cells but smaller doses have no detectable effects.

Research Design and Method

• The researchers used nine adult horses that were in normal health conditions and were not suffering from any trauma.
• The horses were subjected to four different heparin maintenance regimens, which varied in dosage: 320, 240, 160, and 40 U/kg of the horse’s body weight.
• The heparin was derived from pig intestines and was injected subcutaneously (under the skin) every 12 hours for a total of 96 hours.
• A starting dose of one-third the maintenance dose was given intravenously prior to the first heparin injection.
• Three horses, which served as controls, were given an equivalent volume of 0.9% saline solution.

Results and Findings

• The two largest doses of heparin, the 320 U/kg and 240 U/kg doses, extended the therapy range for heparin anticoagulation, as measured by prolongation of activated partial thromboplastin time (APTT).
• The 160 U/kg dose kept the APTT within the therapeutic range, while the lowest dose (40 U/kg) did not affect the APTT.
• All doses of heparin, except for the lowest one, caused a significant drop in the number of red blood cells, the packed cell volume (PCV), and the total hemoglobin content.
• The 320 U/kg and 240 U/kg doses led to reduced platelet count in the horses.
• As the number of red blood cells decreased, the researchers saw an increase in the mean corpuscular volume (MCV).
• The levels of plasma proteins, serum bilirubin, free hemoglobin in the plasma, plasma haptoglobin, and urine and fecal hemoglobins remained stable in all groups.
• There were no detectable effects from the smallest dose of heparin or from the saline solution.

Conclusions

• The study demonstrates that while heparin can extend the range of anticoagulation therapy in horses, it also drastically affects their red blood cell mass.
• Large doses cause a significant reduction in the number of red blood cells and total hemoglobin content.
• However, the smallest dose tested here (40 U/kg) did not have these effects.
• This could suggest a need for careful dosage consideration in heparin therapy for horses.