Digoxin: Indications, MOA, & Pharmacokinetics

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Questions and Answers

What is the significance of a steady-state serum digoxin level of 0.5 ng/mL for BH?

It confirms an appropriate therapeutic level for BH currently. (correct)

It shows digoxin is below the therapeutic range for heart failure.

It means the dose of digoxin is too high and should be decreased.

It indicates digoxin is not being absorbed.

What could be a reason for BH's physician to want to increase the digoxin dose?

To achieve a higher therapeutic effect. (correct)

To improve renal function.

To prevent digoxin toxicity.

To reduce the side effects of the drug.

What initial dosing strategy would the physician likely choose for digoxin considering its half-life?

Dosing every other day.

Dosing once daily. (correct)

Dosing twice daily.

Dosing weekly.

What is the main concern when adjusting the digoxin dose for a patient like BH?

Potential for increased adverse effects and toxicity. Signup and view all the answers

How is digoxin primarily eliminated from the body?

Renal excretion. Signup and view all the answers

What is the primary use of Digoxin?

Heart failure and supraventricular arrhythmia Signup and view all the answers

What is the typical bioavailability of Digoxin tablets?

0.7 Signup and view all the answers

What is the range of Digoxin distribution in the body?

4 to 9 L/kg Signup and view all the answers

What are the recommended loading doses for Digoxin?

It is no longer recommended Signup and view all the answers

What is a major adverse event associated with Digoxin use?

Arrhythmia Signup and view all the answers

Which statement is true regarding Digoxin absorption?

Elixir has a higher bioavailability than tablets Signup and view all the answers

How should Digoxin dosage be based in practice?

Ideal body weight (IBW) Signup and view all the answers

What characteristic of Digoxin's pharmacokinetics is highlighted in its usage?

Narrow therapeutic index Signup and view all the answers

What is the main route of elimination for digoxin?

Renal excretion Signup and view all the answers

What parameter is used to calculate the metabolic clearance (CLm) for patients with moderate to severe heart failure?

20 mL/min Signup and view all the answers

What is the half-life (t1/2) of digoxin?

2 days Signup and view all the answers

How is the clearance (CL) of digoxin affected in patients with mild heart failure (HF)?

CL is similar to patients without heart failure Signup and view all the answers

What is the formula for determining the maintenance dose (MD) of digoxin?

MD = Css x ! x 106 x F Signup and view all the answers

What target steady-state plasma concentration (Css) is typically used for patients with heart failure?

0.5 - 0.9 ng/mL Signup and view all the answers

Which formula allows for the calculation of the desired concentration of digoxin at a specific time?

CDESIRED = Css x e^(-kt) Signup and view all the answers

What is the dosing interval (t) in minutes when calculating the maintenance dose for digoxin over one day?

1440 minutes Signup and view all the answers

Study Notes

Digoxin: Indications, MOA, & Loading Doses

Class and MOA: Digoxin is a cardiac glycoside that acts as a sodium-potassium ATPase inhibitor. It increases myocardial contractility and decreases heart rate.
Indications: Primarily used for heart failure and atrial fibrillation, but also used for supraventricular arrhythmias.
Loading Doses: While loading doses were previously common, current practice favors alternative therapies due to the potential for toxicity.

Digoxin: Adverse Events

Main Adverse Event: Cardiac arrhythmias due to digoxin toxicity.
Visual Symptoms: The most common symptom is seeing a yellow-green halo.

### Digoxin: Pharmacokinetics

Absorption: Bioavailability varies between oral dosage forms, tablets are ~70% and elixir is ~80%.
Distribution: Ranges from 4 to 9 L/kg, with an average value of 7 L/kg used in practice. Always use ideal body weight (IBW) for calculations.
Metabolism: Primarily metabolized by the liver, with minimal bacterial metabolism in the large intestine.
Elimination: Renally excreted, with approximately 70% being eliminated unchanged. The half-life is around 2 days.

Digoxin: Pharmacokinetic Calculations

Population-Based Clearance: Calculated using the following equation: CL = (1.303 x CrCl*) + CLm.
- CLm (metabolic clearance) is 40 mL/min for patients with no or mild heart failure and 20 mL/min for patients with moderate to severe heart failure.
Patient-Specific Clearance: Calculated using the following equation: CL = MD x 106 x F / Css x !
- MD: Maintenance dose in mg/day
- F: Bioavailability
- Css: Steady-state plasma concentration in ng/mL
- !: Dosing interval in minutes (1440 minutes = 1 day)

Digoxin: Dosing Calculations

Calculation #1 - Maintenance Dose: MD = Css x CL x ! / 106 x F
- Css: Steady-state plasma concentration in ng/mL
- Goal for heart failure: 0.5 - 0.9 ng/mL
- Goal for atrial fibrillation: 1 - 2 ng/mL
- !: Dosing interval in minutes (1440 minutes = 1 day)
Calculation #2 - Time to Desired Level: CDESIRED= Css x e-kt
- t: Time required to reach the desired level

### Digoxin: Practice Problems

Practical Considerations:
- Given the long half-life of digoxin, it is typically administered once daily.
- Once a steady-state serum digoxin level is achieved, it can be used to calculate the patient's real clearance.
- This allows for adjustments in the maintenance dose to achieve a desired serum concentration.

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Description

This quiz covers the vital aspects of Digoxin, including its indications, mechanism of action, loading doses, and pharmacokinetics. Understand the essential details about how Digoxin functions, its uses in heart conditions, and the significance of dosing. Test your knowledge on potential adverse effects and absorption rates.