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Treatment of ventricular tachycardia
vaccine against Lyme disease last month. The vaccine is approved for use in people between the ages of 15 and 70, and is given in three doses over a one-year period. Side effects of the vaccne include redness, soreness and swelling at the injection site, and sometimes mild to moderate flu-like symptoms. The Centers for Disease Control and Prevention report that since Lyme disease tracking in the US began in 1982, over 99,000 cases have been reported, mostly from the northeast, upper midwest, and Pacific coastal states.
Treatment of ventricular tachycardia Speaking at the 1998 Bain-Fallon lectures, Dr. Virginia Reef said that treatment of ventricular tachycardia is indicated if the horse is showing clinical signs at rest attributable to the dysrhythmia, the rate is excessively high, the rhythm is multiform or R on T complexes are detected. If pulmonary edema is present emergency treatment should be instituted as soon as possible and should include inu'avenous furosemide (1 - 2 mg/kg), intranasal oxygen and drugs to reduce anxiety, if needed. Lidocaine (without epinephrine) is readily available and is the most rapidly acting drug but must be administered carefully and in small doses (0.25 - 0.5 mg/kg slowly as a bolus) due to the excitement and seizures associated with larger doses. Diazepam (0.05 mg/kg intravenously) may be used to control the excitability or seizures that may result from lidocaine. The therapeutic plasma concentration of lidocaine is 1.5 - 5 gg/ml. Quinidine gluconate (0.5 - 2.2 mg/kg intravenously as a bolus), procainamide (1 mg/kg/min intravenously) and propafenone (0.5 - 1 mg/kg in 5% dextrose intravenously) are either administered more slowly or in graded doses. All have negative inotropic effects when administered at high doses but are often very effective in converting ventricular tachycardia in horses. The principal metabolite of procainamide is N-acetylprocainamide (NAPA), which is also pharmacologically active. The half-life for procainamide administered intravenously is 3.5 _+ 0.6 hours and for N-acetylprocainamide is 6.3 + 1.5 hours. The therapeutic plasma concentration for procainamide is thought to be 4 - 10 gg/ ml, for N-acetylprocainamide 7 - 15 gg/ml and for procainamide and NAPA together 10 - 30 gg/ml. Intravenous propafenone, if available, should be reserved for horses with refractory ventricular tachycardia. Therapeutic plasma concentrations appear to be between 0.2 - 3.0 gg/ml in horses. Propranolol (0.03 mg/kg intravenously) also has negative inotropic effects and is rarely successful in converting horses with ventricular tachycardia. Propranolol should be tried, however, in horses that do not respond to other antiarrhythmics. Therapeutic plasma concentrations of propranolol may be 20-80 ng/ml in horses. Magnesium sulfate (1 - 2.5 gm/450 kg/minute intravenously) is often effective in refractory ventricu!ar tachycardia in horses, is the drug of choice for quinidine induced t0t:sades de pointes, and has no negative inotropic effects. Magnesium sulfate is effective in horses that are normomagnesemic or hypomagnesemic but is also usually administered slowly. Bretylium tosylate (3 - 5 mg/kg or more intravenously) should be reserved for horses with severe, life threatening ventricular tachycardia or ventricular fibrillation.
Volume 19, Number 1, 1999
Aspirin
Discussions among veterinarians on the Internet reveal varied use of aspirin in horses, especially for uveitis. A dose of 25mg/kg bid for 30 days is being used, based on a paper by Dr, Glenn Severin in the 1993 AAEP Proc. This was used along with Banamine, which Severin also reported to be good for eye pain control, at lmg/kg daily. One practitioner finds aspirin of little va~ue with uveitis until the eye normalizes. Some practitioners use aspirin as an anti-coagulant for laminitis. One report, by Dr. Norman Rantanen, suggested aspirin might be beneficial in racehorses that naturally tend to have platelet aggregation during racing. Another suggestion is that aspirin might be helpful against catheter-associated jugular vein thrombosis. According to at least one practitioner, aspirin at doses of 120 to 240 grains daily may result in a higher incidence of gastric ulcers. Aspirin is widely used in Europe post and pre-competition because of the relatively high background levels in urine which are permitted by the FEI because of dietary sources which cannot be avoided.
Diclazuril
Dr. Tom Tobin reports that a published report at the 8th International Conference on Equine Infectious Diseases had an incorrect plasma level reported for a dose of 5 mg/kg/day. JEVS repeated the incorrect dosage in volume 18, number 12, page 815. Studies at the University of Kentucky found that a dose of 5 mg/kg/day results in a steady state plasma concentration of about 8 gg/ml, with a plasma half life of about 50 hours.
1998 Bain-Fallon Lectures, Australia. See report at: www.equinevetnet.com/horses/ vetmeetings
33
Treatment of ventricular tachycardia Speaking at the 1998 Bain-Fallon lectures, Dr. Virginia Reef said that treatment of ventricular tachycardia is indicated if the horse is showing clinical signs at rest attributable to the dysrhythmia, the rate is excessively high, the rhythm is multiform or R on T complexes are detected. If pulmonary edema is present emergency treatment should be instituted as soon as possible and should include inu'avenous furosemide (1 - 2 mg/kg), intranasal oxygen and drugs to reduce anxiety, if needed. Lidocaine (without epinephrine) is readily available and is the most rapidly acting drug but must be administered carefully and in small doses (0.25 - 0.5 mg/kg slowly as a bolus) due to the excitement and seizures associated with larger doses. Diazepam (0.05 mg/kg intravenously) may be used to control the excitability or seizures that may result from lidocaine. The therapeutic plasma concentration of lidocaine is 1.5 - 5 gg/ml. Quinidine gluconate (0.5 - 2.2 mg/kg intravenously as a bolus), procainamide (1 mg/kg/min intravenously) and propafenone (0.5 - 1 mg/kg in 5% dextrose intravenously) are either administered more slowly or in graded doses. All have negative inotropic effects when administered at high doses but are often very effective in converting ventricular tachycardia in horses. The principal metabolite of procainamide is N-acetylprocainamide (NAPA), which is also pharmacologically active. The half-life for procainamide administered intravenously is 3.5 _+ 0.6 hours and for N-acetylprocainamide is 6.3 + 1.5 hours. The therapeutic plasma concentration for procainamide is thought to be 4 - 10 gg/ ml, for N-acetylprocainamide 7 - 15 gg/ml and for procainamide and NAPA together 10 - 30 gg/ml. Intravenous propafenone, if available, should be reserved for horses with refractory ventricular tachycardia. Therapeutic plasma concentrations appear to be between 0.2 - 3.0 gg/ml in horses. Propranolol (0.03 mg/kg intravenously) also has negative inotropic effects and is rarely successful in converting horses with ventricular tachycardia. Propranolol should be tried, however, in horses that do not respond to other antiarrhythmics. Therapeutic plasma concentrations of propranolol may be 20-80 ng/ml in horses. Magnesium sulfate (1 - 2.5 gm/450 kg/minute intravenously) is often effective in refractory ventricu!ar tachycardia in horses, is the drug of choice for quinidine induced t0t:sades de pointes, and has no negative inotropic effects. Magnesium sulfate is effective in horses that are normomagnesemic or hypomagnesemic but is also usually administered slowly. Bretylium tosylate (3 - 5 mg/kg or more intravenously) should be reserved for horses with severe, life threatening ventricular tachycardia or ventricular fibrillation.
Volume 19, Number 1, 1999
Aspirin
Discussions among veterinarians on the Internet reveal varied use of aspirin in horses, especially for uveitis. A dose of 25mg/kg bid for 30 days is being used, based on a paper by Dr, Glenn Severin in the 1993 AAEP Proc. This was used along with Banamine, which Severin also reported to be good for eye pain control, at lmg/kg daily. One practitioner finds aspirin of little va~ue with uveitis until the eye normalizes. Some practitioners use aspirin as an anti-coagulant for laminitis. One report, by Dr. Norman Rantanen, suggested aspirin might be beneficial in racehorses that naturally tend to have platelet aggregation during racing. Another suggestion is that aspirin might be helpful against catheter-associated jugular vein thrombosis. According to at least one practitioner, aspirin at doses of 120 to 240 grains daily may result in a higher incidence of gastric ulcers. Aspirin is widely used in Europe post and pre-competition because of the relatively high background levels in urine which are permitted by the FEI because of dietary sources which cannot be avoided.
Diclazuril
Dr. Tom Tobin reports that a published report at the 8th International Conference on Equine Infectious Diseases had an incorrect plasma level reported for a dose of 5 mg/kg/day. JEVS repeated the incorrect dosage in volume 18, number 12, page 815. Studies at the University of Kentucky found that a dose of 5 mg/kg/day results in a steady state plasma concentration of about 8 gg/ml, with a plasma half life of about 50 hours.
1998 Bain-Fallon Lectures, Australia. See report at: www.equinevetnet.com/horses/ vetmeetings
33