Table 7.4.

Antiarrhythmic drugs

Drug	Therapeutic dose	Therapeutic serum level and effect	Toxicity
Digoxin	LD: 0.5 mg (2 capsules) every 8 h for 48 h 1.5 mg/d for 2 days	0.7-2.0 ng/mL	Maternal nausea/vomiting, sinus bradyarrhythmia or AVB, proarrhythmia
	MD: 0.250.75 mg/day Fetal IM dose: 88 µg/kg every 12 h, repeat twice	Nausea, fatigue, loss of appetite, sinus bradycardia, first-degree AV block, nocturnal Wenckebach AV block (rare)	Fetal IM: sciatic nerve injury or skin laceration from injection
Sotalol	160480 mg/day every 812 h PO	Levels not monitored	Nausea/vomiting, dizziness, QTc ≥ 0.48 s, fatigue, BBB, maternal/fetal proarrhythmia
		Bradycardia, first-degree AVB, P and QRS widening, QTc ≤ 0.48 s
Amiodarone	LD: 18002400 mg/d divided every 6 h PO	0.72.0 µg/mL	Nausea/vomiting, thyroid dysfunction, photosensitivity rash, thrombocytopenia, BBB, QTc ≥ 0.48 s, maternal/fetal proarrhythmia, fetal torsades with LQTS, fetal goiter, neurodevelopmental concerns
	MD: 200600 mg/d PO	Maternal/fetal sinus bradycardia, decreased appetite, first-degree AVB, P and QRS widening, QTc ≤ 0.48 s
	Consider discontinuation of drug and transition to another agent once normal rhythm is reestablished or hydrops has resolved.
Propranolol	60320 mg/d divided every 6 h PO	25-140 ng/mL	Fatigue, bradycardia, hypotension, AV block, fetal growth restriction, increased uterine tone
		First-degree AVB, bradycardia, increased uterine tone
Lidocaine	LD: 11.5 mg/kg followed by infusion of 14 mg/min continuous IV	1.5-5 µg/mL	Nausea/vomiting, neurological symptoms, proarrhythmia
Mexiletine	600900 mg/d divided every 8 h PO	0.5-2 µg/mL	Nausea/vomiting, neurological symptoms, proarrhythmia
Magnesium sulfate	LD: 26 g IV over 20 min followed by 12 g/h	< 6 mEq/L	Fatigue, neurological symptoms If there is loss of patellar reflex and/or levels of> 6 mEq/L STOP infusion
	Treatment for > 48 h is not recommended but redosing may be considered if VT recurs	Monitor patellar reflex	Levels > 5 mEq/L associated with maternal changes on ECG and proarrhythmia

AV: atrioventricular; AVB: atrioventricular block; BBB: bundle-branch block; ECG: electrocardiogram; IM: intramuscular; IV: intravenous; LD: loading dose; LOE: level of evidence; LQTS: long QT syndrome; MD: maintenance dose; PO: orally; VT: ventricular tachycardia.

Source: afapted from Donofrio et al.¹⁷