Practical aspects of monitoring cardiac drugs in the blood.

Various factors known to affect digoxin blood values are discussed in the present review. A reduction as well as an increase in digoxin levels may be due to the method employed, to errors in the preanalytical phase, to peculiarities of the patient, to diseases or to the administration of drugs. Increased digoxin concentrations above the therapeutic range are much more common than manifestations of digoxin intoxication. However, geriatric patients are specially sensitive to intoxication. Attention has to be paid to digoxin-like immunoreactive factors (DLIF) being synthesized under certain physiologic and pathophysiologic conditions which cause falsely elevated values in digoxin-immunoassays. The determination of digoxin levels is indicated in suspected intoxication or hypersensitivity to digoxin, in patients with pacemakers or those receiving certain drugs, in old people and in patients suffering from any concomitant disease. The time of blood collection has to be carefully controlled in order to determine digoxin concentrations of diagnostic value, the physical activity of the patient being a main influencing factor.