Digoxin plasma concentration

Quinidine [HP] Increased digoxin plasma concentrations displaces digoxin from tissue binding sites. 

CARVEDILOL DIGOXIN Carvedilol may t digoxin plasma concentrations, particularly in children i P-gp-mediated renal clearance of digoxin 1 the dose of digoxin by 25% watch for signs of digoxin toxicity and monitor digoxin levels... 

ST JOHN S WORT CARDIAC GLYCOSIDES -DIGOXIN Plasma concentrations of digoxin seem to be 1 by St John s wort St John s wort seems to i P-gp-mediated intestinal absorption of digoxin Watch for l response to digoxin... 

RIFAMPICIN DIGOXIN Plasma concentrations of digoxin may be 1 by rifampicin Rifampicin seems to induce P-gp-mediated excretion of digoxin in the kidneys Watch for l response to digoxin, check plasma levels and t dose as necessaiy... 

QUININE CARDIAC GLYCOSIDES-DIGOXIN Plasma concentrations of digoxin may T when it is co administered with quinine Uncertain, but seems to be due to 1 non-renal (possibly biliary) excretion of digoxin Monitor digoxin levels watch for digoxin toxicity... 

FIGURE 2.6 Expected digoxin plasma concentrations after administering perfectly matched loading and maintenance doses (solid line), no initial loading dose (bottom dashed line), or a loading dose that is large in relation to the subsequent maintenance dose (upper dashed line). 

In a retrospective analysis of 210 randomly selected digoxin plasma concentration determinations in inpatients, the indications were considered to have been inappropriate in 67, appropriate in 81, and unevaluable in 4 (317). Timing of the blood sample was wrong in 17 cases (samples should be taken at least 6 hours and preferably about 11 hours after the dose). Of the measurements whose indications were considered to have been inappropriate, most (52) were performed as part of routine monitoring. 

The interaction between macrohdes and digoxin is not a consequence of altered cytochrome P450 activity. Digoxin is metabolized in the gastrointestinal tract by Eubacterium lentum in the bowel flora of about 10% of patients (106). The direct antibacterial effect of macrohdes reduces digoxin metabolism and increases its systemic availabihty (134). The resultant increased digoxin plasma concentrations are associated with severe nausea, vomiting, and dysrhythmias (105,145,146). 

Which one of the following drugs increases digoxin plasma concentration by a pharmacokinetic mechanism ... 

Belz GG, AustPE, Munkes R. Digoxin plasma concentrations andnifedipine. Lancet 9 ) i, 844-5. 

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