Page 1003 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

978 CHAPTER 8

VetBooks.ir Table 8.4 Common drugs used in the management of cardiovascular disease

DIGOXIN
• Main application. Slow heart rate during heart failure. Increases cardiac output. Also used in the management of supraventricular
tachyarrhythmia. Does not treat arrhythmia directly but slows rate through decreased AV nodal conduction
• Toxic effects. Depression, anorexia and colic are common. Bradycardia, total AV block, ventricular tachyarrhythmias are all
possible. Interaction with quinidine may increase potential for toxic effects. Predisposed by hypokalaemia, hypoproteinaemia,
dehydration and renal disease
• Dose. 0.011 mg/kg p/o or 0.0022 mg/kg i/v q12–24 h. An initial i/v dose is often recommended. I/v administration is indicated if
used to treat quinidine-associated tachycardia. Dose should be reduced by up to 50% if used concurrently with quinidine. Low
therapeutic index, therefore monitoring of blood levels is indicated. Therapeutic range 1–2 ng/ml
QUINIDINE
• Main application. Most commonly used in the management of AF. Also used in treatment of other supraventricular and
ventricular arrhythmias. Quinidine sulphate (oral) is administered via nasogastric tube and is used mainly in the management of
AF. Quinidine gluconate is administered i/v and used in the management of acute AF (<4 weeks) or ventricular arrhythmias
• Toxic effects. Variable. Mild signs such as depression, nasal oedema and increased frequency of defaecation are common and are
often tolerated. More severe signs such as marked hypotension, ataxia, colic, diarrhoea, laminitis, sustained tachycardia, syncope
and sudden death have been reported. Idiosyncratic responses may occur with first dose. Torsades de pointes may be more likely
in hypokalaemic patients
• Dose. Quinidine gluconate: 0.5–2.2 mg/kg i/v bolus q5–10 min to effect, maximum dose 12 mg/kg. Often conversion of
ventricular tachycardia occurs with one dose at 0.5 mg/kg. Quinidine sulphate: 22 mg/kg via nasogastric tube q2 h until
conversion, toxic effects, therapeutic levels or six doses. Continue administration every 6 hours until conversion or adverse
effects. Monitor ECG closely during treatment. Heart rate >80 bpm, widening of QRS complexes to 125% of the pre-treatment
width and abnormal complexes are all indicators to cease medication. Therapeutic range 3–5 μg/ml
LIDOCAINE (WITHOUT ADRENALINE [EPINEPHRINE])
• Main application. Emergency treatment for ventricular arrhythmias. Does not have effects on supraventricular arrhythmias.
Intravenous boluses are used in acute cases, while slow i/v administration is used in subacute cases. Short duration of action
• Toxic effects. Horses are very susceptible to lidocaine-induced CNS signs. Excitability, muscle fasciculations and convulsions
may occur after i/v bolus. Ventricular tachycardia and sudden death have been reported
• Dose. 0.25 mg/kg bolus. 0.5–1.0 mg/kg slowly to effect. Can repeat in 5–10 minutes. 20–50 mg/kg/min CRI. Therapeutic
concentrations 1.5–5.0 μg/ml
MAGNESIUM SULPHATE
• Main application. Treatment of quinidine-induced torsades de pointes. Has been used in the management of ventricular
arrhythmias that were not responsive to other antiarrhythmic medications
• Toxic effects. Colic and syncope have been reported
• Dose. 1.0–2.5 g/450 kg/min over 20–30 minutes. Do not exceed 25 g total dose
FUROSEMIDE
• Main application. Used in the management of heart failure to decrease volume overload and therefore decrease vascular volume
and cardiac workload. Will only have effect if cardiac output is sufficient for adequate renal perfusion
• Toxic effects. Prolonged or aggressive use will cause dehydration, azotaemia, electrolyte abnormalities and metabolic alkalosis.
• Dose. 0.5–1.0 mg/kg i/v, i/m or p/o q12 h
PROCAINAMIDE
• Main application. Has been used in the management of AF but is considerably less effective than quinidine. Has been used in the
management of ventricular tachycardia
• Toxic effects. Similar to quinidine. Death due to ventricular arrhythmia has occurred during treatment for AF
• Dose. 1 mg/kg/min i/v, not exceeding a 20 mg/kg total dose; 25–35 mg/kg p/o q8 h.
PROPRANOLOL
• Main application. Has been used in the management of ventricular tachycardia. Decreases ventricular rate
• Toxic effects. Bradycardia, AV block and arrhythmias may occur. It is a negative inotrope and may cause hypotension. Use with
caution in animals with airway disease, as it may exacerbate bronchospasm
• Dose. 0.03 mg/kg i/v; 0.38–0.78 mg/kg p/o q8 h

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