28 Questions
What is the main route of elimination for digoxin?
Renal excretion
Which plasma concentration range of digoxin is considered to be within the therapeutic range?
$1-2 rac{ ext{mcg}}{L}$
What percentage of an oral dose of digoxin is absorbed in the small intestine?
70-80%
What is the loading dose range for digoxin?
$0.01-0.02 rac{ ext{mg}}{kg}$
What percentage of digoxin is eliminated by nonrenal routes?
~25-28%
Which patients require dosage adjustments for digoxin due to their condition?
Patients with congestive heart failure (CHF)
What is the approximate percentage of unchanged digoxin excreted in urine?
Nearly all
What is the long elimination half-life for adults receiving ionotropic agents like digoxin?
Once daily
What is the recognized therapeutic range of dihydrodigoxin as a metabolite?
Remains to be resolved
What might rise up to 30% of a given dose due to variation?
Biliary excretion
What seems to be of minor importance in the elimination process according to the text?
Enterohepatic cycle
What is the range of metabolic clearance of digoxin in mL/kg/min?
0.57 to 0.86
What is the effect of St. John’s wort on the bioavailability of digoxin in healthy individuals via intravenous route?
Decreases by 25%
What can alter digoxin concentrations and clearance?
Antibiotics, particularly macrolides
What is the half-life range of digoxin?
7 to 14 days
Where should routine plasma samples for digoxin monitoring be obtained?
Just before the next dose
What percentage of digoxin is free in blood plasma?
70-80%
What is the total digoxin clearance (Clt) in elixir form?
0.8
How long does it take to achieve steady state for digoxin?
15 to 20 days
What factors can affect the volume of distribution of digoxin?
Creatinine clearance, hypothyroidism, and obesity
In which model does the distribution of digoxin follow?
Two-compartment model
When do plasma digoxin levels accurately reflect the drug’s pharmacological effect?
After equilibration is complete
What is the range of metabolic clearance of digoxin in mL/kg/min?
0.57 - 0.86
What is the total digoxin clearance (Clt) in elixir form?
0.8
What percentage of digoxin is free in blood plasma?
70-80%
What might alter digoxin concentrations and clearance?
Antibiotics, particularly macrolides
What is the recognized effect of St. John’s wort on the bioavailability of digoxin in healthy individuals via intravenous route?
-25%
What is the half-life range of digoxin?
7 - 14 days
Study Notes
Pharmacokinetics of Digoxin
- Digoxin clearance varies between 0.5 and 0.9 in tablet form and 0.8 in elixir form.
- Total digoxin clearance (Clt) is the sum of metabolic (Clm) and renal (Clr) clearances.
- Metabolic clearance of digoxin ranges from 0.57 to 0.86 mL/kg/min.
- Bioavailability in healthy individuals via intravenous route is 100%, but it decreases by 25% with St. John’s wort.
- Antibiotics, particularly macrolides, can alter digoxin concentrations and clearance.
- The half-life of digoxin ranges from 7 to 14 days, and it takes 15 to 20 days to achieve steady state.
- Digoxin is extensively distributed in tissues, with 70-80% free in blood plasma.
- Volume of distribution is affected by factors such as renal function, hypothyroidism, and drug interactions.
- Routine plasma samples for digoxin monitoring should be obtained just before the next dose.
- Pharmacokinetics of digoxin is altered in patients with end-stage renal disease and hypothyroidism.
- The distribution of digoxin follows a two-compartment model, with initial high serum concentrations not reflective of therapeutic or toxic potential.
- Plasma digoxin levels may not accurately reflect the drug’s pharmacological effect until after equilibration is complete.
Pharmacokinetics of Digoxin
- Digoxin clearance varies between 0.5 and 0.9 in tablet form and 0.8 in elixir form.
- Total digoxin clearance (Clt) is the sum of metabolic (Clm) and renal (Clr) clearances.
- Metabolic clearance of digoxin ranges from 0.57 to 0.86 mL/kg/min.
- Bioavailability in healthy individuals via intravenous route is 100%, but it decreases by 25% with St. John’s wort.
- Antibiotics, particularly macrolides, can alter digoxin concentrations and clearance.
- The half-life of digoxin ranges from 7 to 14 days, and it takes 15 to 20 days to achieve steady state.
- Digoxin is extensively distributed in tissues, with 70-80% free in blood plasma.
- Volume of distribution is affected by factors such as renal function, hypothyroidism, and drug interactions.
- Routine plasma samples for digoxin monitoring should be obtained just before the next dose.
- Pharmacokinetics of digoxin is altered in patients with end-stage renal disease and hypothyroidism.
- The distribution of digoxin follows a two-compartment model, with initial high serum concentrations not reflective of therapeutic or toxic potential.
- Plasma digoxin levels may not accurately reflect the drug’s pharmacological effect until after equilibration is complete.
Test your knowledge on the ionotropic agent primarily used to treat atrial fibrillation in patients with congestive heart failure (CHF). Explore dosage, administration, and considerations for patients with renal impairment.
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