Objective—To determine pharmacokinetic variables
and to evaluate the influence on clotting times after
SC administration of single doses of dalteparin and
enoxaparin to horses.
Animals—5 healthy adult horses.
Procedure—The study was designed as a 4-period
crossover study. Each horse received a single SC
injection of dalteparin (50 and 100 anti-Xa U/kg) and
enoxaparin (40 and 80 anti-Xa U/kg). Plasma anti-Xa
activities and clotting times were measured, and
pharmacokinetic variables were determined.
Absolute and relative maximal prolongation of clotting
times was calculated, and correlation between
plasma anti-Xa activities and clotting times was
Results—The SC administration of each of the doses
of the 2 preparations was well tolerated. Time course
of the anti-Xa activities could be described in a 1-compartment
model. Comparison of low- and high-dose
treatments revealed a disproportionate increase of
the area under the plasma activity-time curve and prolongation
of the terminal half-life, but the increase in
maximum plasma activity was proportionate, and
peak plasma concentrations corresponded with concentrations
recommended in human medicine. There
were only mild changes in activated partial thromboplastin
time (aPTT), whereas the influence on thrombin
time (TT) was greater, dose-dependent, and more
variable. A weak-to-moderate correlation between
aPTT and plasma anti-Xa activities and a moderate-tostrong
correlation between TT and plasma anti-Xa
activities were found.
Conclusion and Clinical Relevance—Pharmacokinetic
and anticoagulatory properties of low-molecular-
weight heparins in horses are similar to those
found in humans. Once-daily SC administration of dalteparin
or enoxaparin may be useful as an anticoagulatory
treatment in horses. (Am J Vet Res 2002;
Objective—To assess the feasibility, describe the techniques, and determine the reliability of transthoracic echocardiography for characterization of left atrial (LA) size and LA mechanical function in horses.
Animals—6 healthy adult horses.
Procedures—Repeated echocardiographic examinations were performed independently by 2 observers in standing, unsedated horses by use of 2-dimensional echocardiography, pulsed-wave flow Doppler, and tissue Doppler imaging (TDI) techniques. Test reliability was determined by estimating measurement variability, within-day interobserver variability, and between-day inter- and intraobserver variability of all echocardiographic variables. Variability was expressed as the coefficient of variation (CV) and the absolute value below which the difference between 2 measurements will lie with 95% probability.
Results—Most echocardiographic variables of LA size had low overall variability (CV, < 15%). Among the 2-dimensional indices of LA mechanical function, area-based and volume-based ejection phase indices had moderate between-day variability (CV usually < 25%). Transmitral Doppler flow indices were characterized by low to high between-day variability (CV, 6% to 35%). The TDI wall motion velocities had high between-day variability (CV, > 25%), whereas most TDI-derived time intervals had low variability (CV, < 15%).
Conclusions and Clinical Relevance—LA size and mechanical function can be reliably assessed in standing, unsedated horses by use of 2-dimensional echocardiography, transmitral blood flow velocity profiles, and analyses of LA wall motion by use of TDI. These results may provide useful recommendations for echocardiographic assessment of LA size and function in horses.