A woman had elevated
serum digoxin levels and signs of
toxicity after she was given
ritonavir. Pharmacokinetic studies have shown that
ritonavir and saquinavir with
ritonavir cause modest to marked increases in single-dose
digoxin levels.
It would seem prudent to closely monitor patients taking
digoxin when
ritonavir is started or stopped. Note that there appears to be a greater effect with
intravenous digoxin than with oral
digoxin. There do not appear to be any reports or studies of the interaction of
digoxin with other
protease inhibitors; however, most
protease inhibitors are inhibitors and/or substrates for P-glycoprotein, so it would seem likely that they may all interact to a greater or lesser degree.