Intravenous infusion of magnesium sulfate and its effect on horses with trigeminal-mediated headshaking

Background: Trigeminal-mediated headshaking results from low-threshold firing of the trigeminal nerve resulting in apparent facial pain. Magnesium may have neuroprotective effects on nerve firing that potentially dampen signs of neuropathic pain. This hypothesis has not been investigated in horses with trigeminal-mediated headshaking. Objective: To investigate head-shaking behavior in affected horses after IV magnesium sulfate infusion. Animals: Six geldings with trigeminal-mediated headshaking. Methods: Prospective randomized crossover study. Horses were controlled for diet and infused IV with 5% dextrose solution (DS; control solution at 2 mL/kg body weight [BW]) and MgSO₄ 50% solution (MSS at 40 mg/kg BW). Head-shaking behavior was recorded at times T0 (baseline, before infusion) and T15, T30, T60, and T120 minutes post-infusion. Venous blood variables such as pH, HCO₃ ⁻, standard base excess (SBE), Na⁺, Cl⁻, K⁺, Ca²⁺, Mg²⁺, total magnesium (tMg), glucose, and lactate were measured; strong ion difference (SID) and anion gap (AG) were calculated for each time point. Results: Blood variables including pH, Na⁺, Cl⁻, K⁺, SID, AG, lactate, Ca²⁺, tMg, and Mg²⁺ had significant changes with MSS as compared to DS treatment. Glucose, SBE, and HCO₃ ⁻ did not have significant changes. A 29% reduction in head-shaking rate occurred after MSS treatment but no change occurred after DS treatment. Conclusions and Clinical Importance: Administration of MSS IV increased plasma total and ionized magnesium concentrations and significantly decreased head-shaking behavior in horses with trigeminal-mediated headshaking.