The effects of exercise training on the pharmacokinetics of digoxin.
BACKGROUND
Studies have shown that digoxin binds to the working muscles during an acute bout of exercise, with a concomitant decrease in serum digoxin concentration. This study investigated the effects of 16 weeks of endurance exercise training on the pharmacokinetics of digoxin in old and young adults.


METHODS
Twelve subjects, aged 68.5 +/- 4.5 years, and six subjects, aged 30.3 +/- 3.8 years, completed the study. All subjects were healthy, sedentary, and taking no cardiovascular medications. After initial testing and maximum oxygen consumption (VO2max) measurements, subjects were hospitalized for 28 hours for renal function testing and digoxin clearance studies and then randomly assigned to an exercise (EG) or control (CG) group. The EG completed 16 weeks (three 1-hour bouts/week) of aerobic training at 75% to 85% of maximum capacity. The CG did not exercise. All tests were repeated at the end of the 16-week study period.


RESULTS
In the older EG subjects, VO2max increased by 3.4 ml/kg/min, or approximately 16% (P = 0.0002). VO2max increased in the younger EG subjects by 1.1 ml/kg/min, but the increase was not significant (P > 0.05). There were no significant changes in body composition, renal function, or time of onset, peak concentration, or elimination phase half-life of digoxin in either the old or young exercise or control groups (P > 0.05 for all variables).


CONCLUSIONS
Although 16 weeks of endurance exercise training improves cardiorespiratory fitness, the pharmacokinetics of digoxin are neither improved nor adversely affected in healthy old and young adults.
Jessup
J V
JV
College of Nursing, University of Florida, Gainesville 32610, USA.
Lowenthal
D T
DT
Pollock
M L
ML
Williams
L
L
Ruiz
J
J
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002316:Cardiotonic Agents / Q000493:pharmacokinetics*; D004077:Digoxin / Q000493:pharmacokinetics*; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D005260:Female; D006207:Half-Life; D006801:Humans; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology
D002316:Cardiotonic Agents; D004077:Digoxin