Effect of volume expansion and furosemide diuresis on the renal clearance of digoxin.

The effect of volume expansion with normal saline and 10% mannitol and increasing urine flow rate with furosemide on the fractional renal clearance of digoxin (CDIG/CIN) was studied in dogs given a constant infusion of digoxin of 0.010 micrograms/kg/min. With saline and mannitol volume expansion CDIG/CIN increased from 0.58 +/- 0.33 (S.D) and 0.54 +/- 0.14, respectively, to 1.28 +/- 0.14 and 1.13 +/- 0.22, respectively (P less than .005), as urine flow increased from 0.5 to 24 ml/min. With furosemide urine flow increased from 0.5 to 22 ml/min but CDIG/CIN remained constant at 0.63 +/- 0.18. We concluded that volume expansion but not urine flow rate substantially increases CDIG/CIN. We speculate that digoxin is at least partially, it not entirely, reabsorbed passively in the proximal tubule.