The effect of age and everyday exercise on steady-state plasma digoxin concentrations

Age-related physiologic changes may significantly alter the disposition and pharmacologic characteristics of many drugs. The elderly are the most frequent users of digoxin because of increased prevalence of atrial fibrillation and congestive heart failure. This study was conducted to confirm the decrease in digoxin concentrations during exercise, to determine if age is a factor in this decrease, and to explore the difference between chronologic age and physiologic age. Eighteen men age 50-85 years were treated with digoxin for more than 1 month before enrolling and had serum digoxin concentrations of 0.4-2.0 micrograms/L. They were evaluated during a 3-hour period in the morning (A.M. dose withheld). Blood samples were obtained every 10 minutes during sequential 60-minute periods of rest (phase I), walking (phase II), and rest (phase III). There were no significant differences in mean concentration between phases II and I (p < 0.76), phases III and phase I (p < 0.70), or phases II and III (p < 0.37). The effect of age was positively correlated with the mean concentration of phase II but was not statistically significant (p < 0.62). Statistically significant correlations were seen only between the exercise phase and serum albumin and Mini-Mental Status Examination scores. We conclude that exercise has minimal, if any, clinically relevant effects on plasma digoxin concentrations. Increasing chronologic age has no influence on a decrease in the concentrations with exercise; a younger physiologic age may play a role.