Torsades de pointes

Background

Drugs that inhibit P450

1. erythromycin
2. biaxin
3. ketoconozole
4. itraconozole

• certain antihistamines like terfandadine or astemizole, inhibit the delayed rectifier potassium channel
• terfenadine is completely metabolized in liver. Once metabolized, has no cardiac activity
• unmetabolized terfenadine has quinidine- like activity- gives torsades
• if P450 enz inhibited by other drug, then will have increase in concentration of unmetabolized terfanadine.

Treatment

1. Magnesium
   1. 1-2gm IV over 1-2 min; then 1-2gm/hr gtt
2. Overdrive pacing
   1. Goal HR 90-120
3. Isoproterenol
   1. 2-8 mcg/min

See Also

• Tachycardia (Wide)
• ACLS (2010 Guidelines)

Source

10/07 DONALDSON (adapted from Tintinalli, Lampe)