The effect of oral isoxsuprine and pentoxifylline on digital and laminar blood flow in healthy horses.

Objective: To quantitate blood flow in the palmar digital artery and dorsal laminae of the hoof in standing, unmedicated, nonsedated horses, and in horses treated with oral isoxsuprine, oral pentoxifylline, and intravenous acetylpromazine as a positive control.

Study Design: Experimental study; treatments administered in a random cross-over design.

Animals: A total of 6 healthy horses selected with at least one nonpigmented forelimb hoof wall and determined to be free of laminitis.

Methods: All horses were instrumented with a flow probe placed around one palmar digital artery under general anesthesia and a laser doppler flow probe placed within a hole in the dorsal hoof wall to measure digital blood flow and laminar perfusion respectively. Baseline readings of palmar digital blood flow and laminar perfusion were recorded before and between treatments. Horses were randomly assigned to one of two groups and treated with either isoxsuprine (1.2 mg/kg, orally twice daily for 10 days) or pentoxifylline (4.4 mg/kg, orally every 8 hours for 10 days) in a random cross-over design. Digital blood flow (DBF) and laminar perfusion (LP) were measured on days 2, 5, 7, and 10 of treatment. Horses also received acetylpromazine as a positive control (0.066 mg/kg, intravenously) during the washout period, and measurements were taken every 15 minutes until measurements returned to baseline readings. Data were analyzed by using repeated measures ANOVA.

Results: Digital blood flow (11.2 to 97.7 mL/min) and laminar perfusion (1.0 to 11.1 Capillary Perfusion Units) differed between horses. No statistically significant increases in DBF or LP were detected over the 10 day treatment period with either isoxsuprine or pentoxifylline. Acepromazine resulted in a significant increase (P = .0007) in DBF for approximately 75 minutes beginning 15 minutes after treatment. A mild but insignificant increase in LP was identified after acetylpromazine treatment.

Conclusion: Neither isoxsuprine nor pentoxifylline increased blood flow to the digit or dorsal laminae in healthy horses. Acepromazine caused an increased blood flow to the digit. Based on the results of this study acetylpromazine potentially would have a greater effect on improving digital blood flow than oral isoxsuprine or pentoxifylline when treating ischemic conditions of the foot in horses.