Digoxin in dogs: once a day or twice a day?

Healthy mature dogs were given digoxin orally at the same dose once a day (SID) or divided (BID) at 12-hour intervals. Blood concentrations of digoxin were determined by radioimmunoassay. When the drug was given SID, peak blood concentrations were higher than, but lowest blood concentrations were not different than, those obtained when the drug was given BID. Thus, average blood concentration throughout 24 hours was significantly (P less than 0.05) greater when digoxin was given SID than when given BID. This suggested a reduced rate of clearance and an increased risk for toxicosis for digoxin when given SID versus BID. Peaks of digoxin blood concentrations were lower when the drug was given BID rather than SID; however, we do not know whether the smaller fluctuations can be translated into greater efficacy and/or less toxicity. Unless those questions are answered, we recommend that digoxin be administered BID to mature dogs.