Class Ib Antiarrhythmic Agents

Question 1

Class Ib Contraindications

Answer 1

Third-degree AVB

Question 2

Class Ib Adverse Effects

Answer 2

CNS (tremor, seizures,
confusion, vision changes)

Question 3

Lidocaine Drug Interactions

Answer 3

Amiodarone (increased lidocaine concentrations)

Question 4

Lidocaine (Xylocaine) Dosing

Answer 4

Pulseless VT/VF conversion or VT with a pulse: 1–1.5 mg/kg IVP; repeat 0.5–0.75 mg/kg every 3–5 min (max 3 mg/kg)
VT maintenance: 1–4 mg/min

Question 5

Lidocaine Dose Adjustments

Answer 5

If LVEF < 40%, 0.5–0.75 mg/kg IVP
Reduce dose in those with HF, liver disease,
low body weight, and renal dysfunction and in
older adults

Question 6

Mexiletine PK

Answer 6

PK: Half-life 12–20 hr
Substrate CYP2D6, CYP1A2
Inhibitor CYP1A2

Question 7

Mexiletine (Mexitil) Dosing

Answer 7

VT maintenance: 200–300 mg PO every 8 hr;
max 1200 mg/day

Question 8

Mexiletine Dose Adjustment

Answer 8

Reduce dose by 25%–30% in hepatic impairment