Physical exercise and digoxin binding to skeletal muscle: relation to exercise intensity

Area of Science:

• Exercise Physiology
• Pharmacokinetics
• Cardiovascular Pharmacology

Background:

• Digoxin is a cardiac glycoside used to treat heart failure and arrhythmias.
• Understanding digoxin distribution during physical activity is crucial for patient management.
• Skeletal muscle represents a significant reservoir for digoxin in the body.

Purpose of the Study:

• To investigate the impact of bicycle exercise on digoxin concentration in skeletal muscle and serum.
• To determine if exercise intensity influences digoxin distribution.
• To assess the relationship between exercise workload and digoxin uptake into exercised muscle.

Main Methods:

• 10 healthy male subjects ingested 0.5 mg of digoxin daily for 2 weeks.
• Subjects performed two 1-hour bicycle exercise tests at different workloads (70-90 W and 140-180 W) 24 hours after their last dose.
• Digoxin concentrations were measured in skeletal muscle (thigh) and serum post-exercise.

Main Results:

• Lower workload exercise (70-90 W) resulted in a 9% increase in skeletal muscle digoxin (not significant) and a 26% decrease in serum digoxin (p < 0.001).
• Higher workload exercise (140-180 W) led to a 20% increase in skeletal muscle digoxin (p < 0.05) and a 40% decrease in serum digoxin (p < 0.001).
• A significant correlation was observed between exercise intensity and the changes in digoxin distribution.

Conclusions:

• Exercise promotes digoxin redistribution from serum into skeletal muscle.
• The intensity of exercise directly correlates with the magnitude of digoxin uptake into exercised muscle and serum depletion.
• These findings highlight the importance of considering exercise intensity in patients treated with digoxin.