Page 118 - Small Animal Internal Medicine, 6th Edition

90 PART I Cardiovascular System Disorders

The most common toxic effect of lidocaine in dogs is administration to unconscious patients. Cats are particularly
CNS excitation. Signs include agitation, disorientation or sensitive to the drug’s toxic effects and can develop seizures,
VetBooks.ir ataxia, muscle twitches, nystagmus, and generalized seizures; respiratory arrest, bradyarrhythmias, and sudden death. In
the event of toxicity, lidocaine should be discontinued until
nausea also can occur. Worsening of arrhythmias (proar-
rhythmic effect) is seen occasionally, as with any drug that
then be instituted. IV diazepam (0.25-0.5 mg/kg) is used
has cardiac electrophysiologic effects. There are anecdotal the signs of toxicity disappear; a lower infusion rate may
reports of respiratory depression and arrest after lidocaine to control lidocaine-induced seizures. Hepatic disease can

TABLE 4.2
Dosage of Antiarrhythmic Drugs

AGENT DOSAGE

Class I
Lidocaine Dog: initial boluses of 2 mg/kg slowly IV, up to 8 mg/kg (over ≥10 min); or rapid IV infusion at
0.8 mg/kg/min; if effective, then 25-80 mcg/kg/min CRI
Cat: initial bolus of 0.25-0.5 (- 1) mg/kg slowly IV; can repeat boluses of 0.15-0.25 mg/kg, up to
total of 4 mg/kg; if effective, 10-40 mcg/kg/min CRI
Procainamide Dog: 2 mg/kg IV over 2 minutes; repeat if necessary, up to cumulative dose of 20 mg/kg;
10-50 mcg/kg/minute CRI; 6-20 (up to 30) mg/kg IM q4-6h (PO, if available, 10-20 mg/kg
q 8-12 [sustained-release prep.] hours)
Cat: 1.0-2.0 mg/kg IV over 2 minutes, repeat if necessary, up to cumulative dose of 10 mg/kg;
10-20 mcg/kg/min CRI; 7.5-20 mg/kg IM q(6-)8h
Quinidine Dog: 6-20 mg/kg IM q6h (loading dose, 14-20 mg/kg); 6-16 mg/kg PO q6h; sustained action
preparations, 8-20 mg/kg PO q8h
Cat: 6-16 mg/kg, IM or PO, q8h
Mexiletine Dog: 4-6 (-8) mg/kg PO q8h
Cat: —
Phenytoin Dog: 10 mg/kg slowly IV; 20-50 mg/kg PO q8h
Cat: do not use
Propafenone Dog: 2-4 (up to 6?) mg/kg PO q8h (start low)
Cat: —
Flecainide Dog: 1-2 (up to 4?) mg/kg PO q(8-)12h (start low; not advised if CHF or impaired LV function present)
Cat: —
Class II
Atenolol Dog: 0.2-1 mg/kg PO q12(-24)h, start low
Cat: Same, or 6.25(-12.5) mg/cat PO q12(-24)h
Propranolol Dog: 0.02 mg/kg initial bolus slowly IV (up to maximum of 0.1 mg/kg); initial oral dose, 0.1-0.2 mg/
kg PO q8h, up to 1 mg/kg q8h
Cat: Same IV instructions; 2.5 up to 10 mg/cat PO q8-12h
Esmolol Dog: 50-100 mcg/kg IV over 5 minutes (loading dose), followed by infusion of 25-50 mcg/kg/min
Cat: same
Metoprolol Dog: initial dose, 0.1-0.2 mg/kg PO q24(-12)h, up to 1(-2) mg/kg q8(-12)h
Cat: 2 up to 15 mg/cat PO q8(-12)h, start low

Class III
Sotalol Dog: 1-3 (up to 5?) mg/kg PO q12h
Cat: 10-20 mg/cat PO q12h (or 2-4 mg/kg PO q12h)
Amiodarone Dog: PO loading: 10 (up to 15) mg/kg PO q12h for 4-7 days, then same dose q24h for 7 days, then
reduce to maintenance dose
PO maintenance: 5-7.5 mg/kg PO q24h
For IV administration use aqueous formulation (Nexterone, 1.5 mg/mL), not standard amiodarone, see
p. 95): 3-5 mg/kg slow IV over 15 min; can continue 0.05 mg/kg/min CRI if needed
Cat: IV aqueous formulation (1.5 mg/mL): 2.5 mg/kg slow IV bolus over 15 minutes (optimal dose
uncertain)