One Pill Can Kill: Digitalis

Welcome to One Pill Can Kill, where we get into the weeds with real-life pediatric toxicology cases from the field. Today we focus on a tricky drug: digoxin.

You may have come across adults with digoxin toxicity who presented with nausea, fatigue, and the “halo” visual disturbance commonly described. They may have had an array of tachy or brady dysrhythmias, like atrial tachycardia with block, bidirectional ventricular tachycardia, and slow atrial fibrillation with AV dissociation and a regular ventricular rate.

Adult presentations of digoxin toxicity aren’t infrequent, as there is a narrow difference between the therapeutic and toxic ranges of cardiac glycosides. But children who have unintentionally ingested digoxin present differently: It takes a higher serum concentration of the drug to bring about symptoms, and they may be obtunded and are more commonly bradycardic with heart block. And they can get remarkably sick.

A Critically Ill Kid

You are called to a church and directed to the basement. You are met by a crowd surrounding a 6-year-old child who looks unwell. As you kneel you jump into your calm-in-chaos persona and begin questioning the audience while assessing the child. You quickly elicit that the child is healthy, without medical history, and visited his grandparents’ home for Sunday pancakes before heading to church. During the service the child began to complain of stomach cramps, then suddenly vomited up the pancakes. The family excused themselves from the church and came to the basement, where they called 9-1-1.

The child is awake and looks at you but does not seem scared or in pain. However, he does wince when you pinch his trapezius. If anything, the child seems resigned, and your heart rate goes up as you recognize the hallmarks of a critically ill pediatric patient.

You quickly assess his circulation: His limbs are cool and mottled; you note cyanosis to the lips and immediately recognize his shallow, rapid breathing. You exchange a glance with your partner, who is hustling to attach the monitor and grab a glucose finger stick.

You both know this child is in decompensated shock; you’ve seen septic children before, but this kiddo’s appearance doesn’t match your memory. You open your IV kit and initiate a 20g IV in the left antecubital fossa.

Your partner rips a 12-lead ECG from the printer; you see an irregular, bradycardic rhythm with a rate of 44 and diagnose it as a second-degree type 2 atrioventricular block. The NIBP cycles and shows a blood pressure of 66/38. Temperature is 36.0ºC, and oxygen saturation 95%.

Pop quiz: What is the low limit of normal for blood pressure in a pediatric patient?

You debate starting CPR on this child, given the low heart rate, but can’t bring yourself to do chest compressions on a child who can follow commands. You begin a 20-cc/kg IV bolus of crystalloid fluid while contemplating a dopamine infusion.

En route the fluid bolus finishes, and you reassess: no change. You try atropine, which increases the heart rate by five. Given your suspicions of toxic overdose, you run through the One Pill Can Kill series and think there must be a cardiac suppressant on board, perhaps a misplaced pill from the grandparents’ house. You pull out a bag of dopamine along with your smartphone and do some math while priming the microdrip set.

The remainder of the drive seems like it takes hours, but only 20 more minutes have passed by the time you arrive at the emergency department. Your partner swings open the back doors and says, “Wow, what did you do? Lookin’ way better!”

You glance down and realize the child is more awake with improving skin color. Your blood pressure cycles and reads 80/45, while the heart rate is now 55. You hand off to the emergency room team. You later learn the child had a high digoxin level and was given an antidote and sent to the ICU, where he recovered.

Quiz answer:

• If age greater than 1 year: (Age x 2) + 70 mm Hg;
• If age 1–12 months: 70 mm Hg;
• If age less than 30 days: 60 mm Hg. Remember, blood pressure drops are ominous in children—they compensate well, then crash hard.

Treating Digoxin Toxicity

In any toxic overdose, the same approach can be used: resuscitation, decontamination, antidotes, dialysis, and supportive care. In the case of digoxin, resuscitation focuses on blood pressure support. Beginning with fluid is reasonable, but vasopressors and inotropic support are mainstays of stabilization. Considering life-threatening potassium fluxes also important.

Decontamination with charcoal can be considered at a 10:1 ratio of charcoal to digoxin. As digoxin doses are small, sometimes a tablespoon of charcoal is sufficient, which can be mixed with chocolate milk to appease children. Gastric lavage may be considered when other drugs are combined with digoxin, usually in intentional overdose situations.

While digoxin is not amenable to dialysis because of its large volume of distribution and high protein binding property, there is an antidote. Fragmented antibodies can bind and deactivate digoxin; this drug is readily available in emergency departments. Supportive care includes monitoring and correcting potassium swings, which often correct on their own with antidote administration.

Other Forms of Digitalis

Children may get their hands on digoxin pills, but the world is full of other cardiac glycosides; foxglove, milkweed, oleander, and lily of the valley are common botanicals that contain glycosides that can cause digitalis toxicity.

After a decade working as a helicopter paramedic, Blair Bigham, MD, MSc, EMT-P, completed medical school in Ontario, Canada, where he is now a resident physician in the emergency department. He has authored over 30 scientific articles, led major national projects to advance prehospital research and participated in multiple collaboratives, including the Resuscitation Outcomes Consortium.