Onset of Action for 250 mcg Digoxin
A 250 microgram (mcg) dose of oral digoxin typically produces a detectable effect within 0.5 to 2 hours, with peak effects occurring between 2 to 6 hours after administration. 1
Pharmacokinetic Profile of Digoxin
- Oral digoxin has a bioavailability of approximately 60-80%, with absorption occurring primarily in the proximal small intestine 2
- The onset of pharmacologic effect after oral administration is observed within 0.5 to 2 hours 1
- Peak plasma concentrations are reached within 2-6 hours after oral administration 1
- Digoxin has an elimination half-life of 36-48 hours in patients with normal renal function 3
- Approximately 50-70% of the drug is excreted unchanged in the urine 3
Factors Affecting Onset of Action
- Renal function: Patients with impaired renal function will have delayed clearance of digoxin, potentially prolonging both onset and duration of action 1
- Age: Elderly patients may have altered pharmacokinetics and typically require lower doses (0.125 mg or 0.0625 mg daily) 3
- Food intake: Taking digoxin with food may slightly delay absorption but does not significantly affect bioavailability 1
- Concomitant medications: Certain drugs like amiodarone, diltiazem, verapamil, and some antibiotics can increase plasma digoxin levels and potentially enhance or prolong effects 3, 4
Clinical Applications and Dosing Considerations
- For heart failure patients, a single daily maintenance dose of 0.25 mg (250 mcg) is commonly used in adults with normal renal function 3
- In atrial fibrillation, digoxin is useful for initial control of ventricular rate, with effects beginning within the first few hours of administration 3
- Loading doses are generally not required in stable patients with sinus rhythm 3
- For rapid digitalization in urgent situations, a single initial dose of 500-750 mcg usually produces a detectable effect in 0.5-2 hours 1
Monitoring and Safety Considerations
- Therapeutic serum concentration should be maintained between 0.6 and 1.2 ng/mL 3, 5
- Serum digoxin levels should be checked early during chronic therapy, with samples taken just before the next scheduled dose or at least 6-8 hours after the last dose 1
- Signs of toxicity include confusion, nausea, anorexia, disturbance of color vision, and cardiac arrhythmias 3, 6
- Patients with hypokalemia are at increased risk for digoxin toxicity, making electrolyte monitoring essential 3
Common Pitfalls and Caveats
- Waiting too long to assess clinical response: Remember that initial effects begin within 0.5-2 hours, not days 1
- Failure to adjust dosing in renal impairment: The half-life of digoxin is prolonged in renal failure to over 100 hours 6
- Overlooking drug interactions: Amiodarone can increase serum digoxin levels by up to 100%, potentially leading to toxicity 4
- Higher doses do not necessarily provide additional benefit: Studies show that moderate doses (0.25 mg) provide no additional hemodynamic or autonomic benefit over low doses (0.125 mg) in mild to moderate heart failure 7
- Steady-state concentrations take approximately five half-lives to achieve (typically 1-3 weeks depending on renal function) 1