Digitalis, digitalis antibodies, digitalis-like immunoreactive substances, and sodium homeostasis: a review.
Most pharmacokinetic and biologic attributes of digitalis are age dependent. They are determined in great measure by the chemical structure of the specific cardiac glycoside being used. These effects differ in the intact normal circulation and in heart failure because of the altered autonomic nervous system and hormonal control that exist in the latter. Digitalis is effective only in the presence of myocardial dysfunction, but in a clinical setting, cardiac performance may be difficult to gauge; improved tools are needed for this purpose. The dosages of digoxin recommended for infants and children have been steadily reduced in the past decade, and there is no good evidence that more favorable risk-to-benefit ratios are achieved when higher doses are used or when higher plasma concentrations are sought. Massive digitalis toxicity is a serious, often fatal, complication in young infants, especially when the drug is given parenterally; it may be difficult to diagnose early. The only reliable deterrent for this complication is the adoption of careful safety standards whenever the drug is employed. Experience with digoxin antibodies is still scarce in children, especially in infancy, but their use generally has been associated with a favorable outcome. Endogenous substances that interfere with the digoxin radioimmunoassay (DLIS) occasionally yield clinically relevant, erroneously high, plasma digoxin concentration readings in neonates. An interesting hypothesis currently being investigated is the physiologic and pathologic role of these compounds in sodium hemostasis; they may be part of a putative endogenous NaK-ATP-ase inhibitor involved in the pathogenesis of hypertension and renal diseases.