The use of calcium for digoxin toxicity has long been reported to cause fatal arrhythmias and possibly stone heart (contraction band necrosis), but the origin of this theory has been based on sporadic case reports. A recent retrospective article by Levine, et al attempted to debunk this theory, although we still have a long way to go because the data isn’t great.
Digoxin is a cardiac glycoside that blocks the Na/K ATPase, resulting in increased intracellular sodium concentration. The increase in intracellular sodium then causes increased intracellular calcium in the cardiac myocytes, resulting in more contractility. Potassium levels in digoxin overdose very, depending on whether it is an acute or chronic overdose. Case reports, starting in 1933 depicted patients dying suddenly after receiving intravenous calcium, although the arrhythmia was never noted. Also, some of these patients had underlying conditions that predisposed them to increased serum calcium levels prior to the administration of more calcium. We all use calcium in hyperkalemia to stabilize cardiac myocytes, except in digoxin toxicity due to the reasons listed above.
Levine et al published an interesting article in JEM in 2011. It was a retrospective chart review looking at all cases of digoxin toxicity over a 17 year period. Of the 159 patients identified, 23 of them received some sort of intravenous calcium. No deaths or arrhythmias were noted in the first hour after calcium administration and the mortality was the same between groups that received calcium and those that did not. The article was one of the first to challenge the notion of not using calcium for digoxin overdose with actual data to back it up. The authors noted that their study was limited as it was retrospective (almost no toxicology studies are prospective due to the difficulty of performing these studies) and it looked mostly at chronic digoxin toxicity. The authors stated that their conclusions cannot be applied to acute toxicity. Dr. Gupta and Dr. Hoffman submitted a letter to the editor concerning the above study, identifying some methodological issues (The response was to the epub ahead of print, which is why the response was published before the article). For example, digoxin toxicity was defined by the patient being admitted with that diagnosis and an elevated digoxin level. The symptoms and, more importantly, the arrhythmias were not used to define toxicity. However, the study has opened up the topic for discussion and further studies.
For now, most experts do not recommend calcium for digoxin toxicity because we have better options. The treatment is digoxin Fab fragments (Digi-bind), which binds to the digoxin. Only 5 case reports exist depicting death from calcium in digoxin toxicity, but the risk now is still to high until we have better data available. When you see calcium as an option on your in-service exam or boards, it’s still not the answer. Check back in a few years after more studies are done!
Davey M. Calcium for hyperkalaemia in digoxin toxicity. Emerg Med J 2002;19:183–188.
Gupta, Su, Hoffman, et al. Digoxin and Calcium: The verdict is still out. Emerg Med J. 2009;38:102.
Levine, Nikkanen and Pallin. The effects of intravenous calcium in patients with digoxin toxicity. Emerg Med J. 2011. 40(1):41-46.