Key result
Steady-state oral quinidine does not alter digoxin bioavailability compared to digoxin alone.
Why the study?
Digoxin serum concentration rises in the presence of quinidine, but it is unclear whether quinidine alters digoxin bioavailability.
Does quinidine alter digoxin bioavailability in human subjects?
Does quinidine alter digoxin bioavailability in human subjects?
Absolute Event Rate: 79.5% vs 73.5%
p-value: p=>0.05
Quinidine does not alter digoxin bioavailability, indicating that altered absorption is not the mechanism for the rise in digoxin serum concentration during quinidine co-administration.
Indicates quinidine-digoxin interaction arises via non-absorption mechanisms; leaves open clearance or distribution effects for targeted study.
Digoxin serum concentration rises in the presence of quinidine. To determine whether quinidine alters digoxin bioavailability, six subjects received 1.0 mg of digoxin intravenously alone and by mouth on alternate weeks during steady-state oral quinidine administration. The area under the digoxin concentration:time curves (AUC) and the amount of digoxin excreted in the urine (Xxu) were determined for the 96 hr after each of the four experiments. Values for digoxin bioavailability relative to the corresponding intravenous study in the absence and presence of quinidine were (+/- S.D.) 73.5 +/- 8.6% and 79.5 +/- 22.6% (P greater than 0.05) for serum and 69.8 +/- 6.8% and 70.2 +/- 10.5% (P greater than 0.05) for urine. There was no difference in the steady-state quinidine serum concentration during the 4 days after intravenous and oral digoxin. We conclude that quinidine does not alter digoxin bioavailability and therefore that altered absorption does not explain the rise in digoxin serum concentration in the presence of quinidine.
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Hager et al. (1981) studied this question. Quinidine vs. Absence of quinidine was evaluated on Digoxin bioavailability (serum) (p=>0.05). Steady-state oral quinidine administration did not significantly alter digoxin bioavailability compared to digoxin alone (serum 79.5% vs 73.5%, P>0.05).
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