Frequently discordant results from therapeutic drug monitoring for digoxin: clinical confusion for the prescriber
Background: Digoxin remains a commonly prescribed medication for the treatment of congestive cardiac failure or atrial tachyarrhythmias. Its utility is offset by its narrow therapeutic index requiring regular blood concentration monitoring. Recent evidence suggests that a lower therapeutic range (0.5–0.8 µg/L, or 0.6–1.0 nmol/L) is associated with reduced mortality in patients with congestive cardiac failure. Therapeutic drug monitoring for digoxin is carried out by immunoassays that are well established in routine clinical practice. Laboratories using different immunoassays may be involved in monitoring individual patients throughout the protracted course of therapy. These results should be concordant to ensure consistent dose individualization and optimum clinical management. We have investigated the discordance in digoxin measurements involving five different laboratories across the Adelaide metropolitan area.
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