Digoxin toxicity - An evaluation in current clinical practice

Background: Serum digoxin concentrations (SDCS)are frequently sampled befor e: completion of drug distribution. If elevated, these concentrations may b e misinterpreted, potentially leading to a misdiagnosis of digoxin toxicity . Objectives: To determine the frequency of elevated SDCs (>2.6 nmol/L [>2.0 ng/mL]) obtained at appropriate postdosing intervals and to evaluate the fr equency of clinically defined digoxin toxicity in patients with elevated SD Cs: Methods: The medical records of adult patients with SDCs assayed at 5 gener al hospitals in North Carolina during a 3-month period (May 1 through July 31, 1996) were prospectively evaluated. Data on SDC, inpatient or outpatien t status, and medical or surgical service were collected for all patients. Data on patient demographics, serum chemistry values, indication for digoxi n treatment, clinical evidence of digoxin toxicity, and timing of the blood sample relative to administration of the last dose of digoxin were collect ed for patients with SDCs higher than 2.6 nmol/L (>2.0 ng/mL). Results: Of 3434 SDCs assayed in 2009 patients, 320 (9.3%) were higher than 2.6 nmol/L (>2.0 ng/mL). Fifty-one (15.9%) of the 320 SDCs were drawn at 6 hours or less following a digoxin dose. Sampling time relative to the digo xin dose could not be determined in 70 (21.9%) of the 320 elevated SDCs, le aving 199 (62.2%) of 320 SDCs in 138 patients evaluable for digoxin toxicit y. Eighty-three of the 138 patients had clinical evidence of digoxin toxici ty for an overall incidence of 4.1%. Conclusions: Digoxin toxicity occurs less frequently than historically repo rted. Continued emphasis needs to be placed on obtaining appropriately time d SDCs.