Repeated intravenous dexamethasone administration causes transient changes in leukocyte parameters in healthy warmblood horses.

Overview

• This study investigated how repeated intravenous doses of the steroid dexamethasone affect white blood cell (WBC) parameters in healthy warmblood horses.
• The researchers observed transient changes in leukocyte counts, with notable increases in neutrophils and decreases in other white blood cell types shortly after dexamethasone administration.

Study Design and Methods

• Purpose: To assess the impact of repeated IV dexamethasone administration on leukocyte parameters in healthy adult horses.
• Subjects: Five warmblood mares.
• Dosing regimen: 0.06 mg/kg dexamethasone sodium phosphate IV administered twice at 0 and 24 hours.
• Control: Saline (0.9% sodium chloride) IV injections administered at 48 and 72 hours post-first dexamethasone dose.
• Blood sampling times: 0 (baseline), 6, 12, 24, 30, 36, 48, 72, 96, and 168 hours relative to first dexamethasone administration.
• Analysis: White blood cell parameters measured and evaluated using linear mixed-effects statistical models to identify changes over time.

Key Findings on Leukocyte Parameters

• Leukocyte (White Blood Cell) Count:
  • Increased significantly at 6 hours after dexamethasone administration.
  • Peaked at 6 hours post-dose, exceeding normal reference intervals in some but not all horses.
• Neutrophils:
  • Neutrophil counts increased in all horses, peaking 6 hours post-dexamethasone.
  • Resulted in transient neutrophilia, which is an abnormally high neutrophil count.
• Neutrophil-to-Lymphocyte Ratio:
  • Ratio increased, reflecting the rise in neutrophils concurrent with lymphocyte reductions.
• Lymphocytes, Monocytes, and Eosinophils:
  • Counts were decreased at 6 hours post-dexamethasone.
  • Eosinophils were completely suppressed at this time point.
• Myeloperoxidase Index (an enzyme activity marker for neutrophils):
  • Increased only at 6 hours after the second dexamethasone dose.
• Neut-X and Neut-Y Parameters (markers related to neutrophil function or subpopulations):
  • Neut-X decreased at 12 hours post-dexamethasone.
  • Neut-Y showed no significant changes up to 156 hours after the first dexamethasone dose.

Duration and Recovery

• Most of the altered leukocyte parameters returned to baseline values between 48 and 72 hours after the first dexamethasone injection.
• Suggests that the observed hematological changes are transient and reversible within days.

Conclusions and Clinical Relevance

• Repeated IV administration of dexamethasone causes recognizable but temporary changes in the leukogram of healthy horses.
• Key changes include:
  • Transient neutrophilia and leukocytosis (elevated total white blood cell counts).
  • Increased neutrophil-to-lymphocyte ratio.
  • Marked decreases in lymphocytes, monocytes, and eosinophils.
• Understanding these glucocorticoid-induced changes is crucial for veterinarians interpreting hematologic data from horses undergoing glucocorticoid therapy.
• This knowledge helps avoid misdiagnosis of infection or inflammation when the changes are in fact drug-induced.