The effects of digitalis glycosides might be increased by rises inblood calcium levels, and use of intravenous calcium may result in development of potentially life-threatening digitalis-induced cardiac arrhythmias. Teriparatide appears not to affect thecalcium-mediated pharmacodynamics of digoxin.
There is some evidence that increases or decreases in blood calcium levels can increase or decrease, respectively, effects of digitalis. A patient with congestive heart failure and atrial fibrillation was resistant to actions of digoxin serum levels of 1.5 to 3 nanograms/mL until his serum calcium levels were raised from 1.68 to about 2.13 mmol/L by oral calci
Disodium edetate. Disodium edetate,(See reference number 3-5)which lowers blood calcium levels, has been used successfully in treatment of digitalis toxicity, although less toxic drugs are generally preferred.
Teriparatide. A placebo-controlled study in 15 healthy subjects given digoxin 500 micrograms daily, adjusted to maintain steady-state serum levels in range 1 to 2 nanograms/mL, found that a single 20-microgram subcutaneous dose of teriparatide on day 15 or 16 did not alter calcium-mediated effects of digoxin (systolic time interval), or heart rate. Serum calcium increased slightly,with a maximum increase of
The actions of cardiac glycosides (even now not fully understood) are closely tied up with movement of calcium ions into heart muscle cells. Increased concentrations of calcium outside these cells increase inflow of calcium and this enhances activity of glycosides. This can lead to effective over-digitalisation and even potentially life-threatening arrhythmias. Conversely, a drop in calcium levels can attenuate activity of glycosides. However, clinical relevance of these changes in calcium is not fully established.
The report of deaths associated with digitalis and calcium compounds (published in 1936) seems to be only direct clinical evidence of a serious adverse interaction, although there is plenty of less direct evidence that an interaction is possible. Intravenous calcium should be avoided in patients receiving cardiac glycosides. If that is not possible,it has been suggested(See reference number 7)that it should be given slowly or only in small amounts in order to avoid transient serum calcium levels higher than 7.5 mmol/L,but it seems likely that very large doses of calcium would be required to reach this level, even transiently.
The very slight increases in calcium observed with teriparatide were considered insufficient to increase cardiac sensitivity to digoxin at therapeutic dosage (See reference number 6). Nevertheless, manufacturer of teriparatide still advises caution in patients taking digitalis, because of possibility for transiently raised calcium levels (See reference number 8,9).
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Benson CT,Voelker JR. Teriparatide has no effect on the calcium-mediated pharmacodynamics of digoxin. Clin Pharmacol Ther (2003) 73, 87–94.
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