Applied Pharmacokinetics - Digoxin Lecture Pre-Work

Flashcards based on Applied Pharmacokinetics pre-work lecture notes, covering digoxin formulas, dosing, therapeutic ranges, toxicity, and sampling timings for blood sampling.

What are the two primary clinical indications for digoxin?

Inotropic support in heart failure and rate control in atrial fibrillation

What is the usual daily dose range for digoxin?

$0.125$ to $0.25\text{ mg}$ once daily

What is the bioavailability ($F$) value for digoxin in soft gelatin capsule form?

$$1$$

What is the bioavailability ($F$) value and range for digoxin in tablet form?

$0.7$ (range $0.5$ to $0.8$)

What is the bioavailability ($F$) value for digoxin elixir?

$$0.8$$

What is the bioavailability ($F$) value for IV digoxin?

$$1$$

What is the salt factor ($S$) for digoxin?

$$1$$

What is the generally accepted therapeutic concentration range for digoxin?

$$0.5 - 1.2\text{ mcg/L}$$

What is the specific therapeutic concentration range for digoxin in heart failure patients?

$$0.5 - 0.8\text{ mcg/L}$$

What is the typical therapeutic concentration for digoxin when treating atrial fibrillation?

Usually $< 1.2\text{ mcg/L}$

At what digoxin level is there an increased mortality risk in heart failure patients?

Levels $> 1\text{ mcg/L}$

At what serum level are digoxin toxic effects more likely to occurring in all patients?

Levels $> 2\text{ mcg/L}$

What gastrointestinal ($GI$) symptoms are associated with digoxin toxicity?

Nausea, vomiting, and diarrhea

What cardiovascular ($CV$) effects are associated with digoxin toxicity?

Irregular heartbeat (bradycardia or tachycardia), EKG changes, and hyperkalemia

What visual symptoms are characteristic of digoxin toxicity?

Blurred vision, color changes, and yellow ‘halos’

What is the half-life ($t1/2$) of digoxin in patients with normal renal function?

$$2\text{ days}$$

What is the half-life ($t1/2$) of digoxin in anephric patients?

$$4 - 6\text{ days}$$

What is the average volume of distribution ($Vd$) for digoxin?

$$7.3\text{ L/kg}$$

Which pharmacokinetic model is used to describe digoxin, and how does it distribute?

A two compartment model; it initially distributes to plasma and rapid tissues, then to more slowly equilibrating tissue

In the context of the digoxin two-compartment model, which compartment includes myocardial tissue?

The second compartment ($Vt$)

Why might a digoxin plasma sample drawn too early provide a falsely high level?

It may not reflect complete distribution from the first compartment to the second compartment

How should the patient’s weight be adjusted for digoxin clearance equations in cases of obesity?

Use Ideal Body Weight ($IBW$)

How should the digoxin dose be adjusted for a clinically hypothyroid patient (high $TSH$)?

Decrease the digoxin dose by 30 \text{%}

How should the digoxin dose be adjusted for a clinically hyperthyroid patient (low $TSH$)?

Increase the digoxin dose by 30 \text{%}

What dose adjustment is required when digoxin is co-administered with Amiodarone?

Decrease the digoxin dose by 50 \text{%}

What dose adjustment is required when digoxin is co-administered with Verapamil?

Decrease the digoxin dose by 25 \text{%}

What dose adjustment is required when digoxin is co-administered with Quinidine?

Decrease the digoxin dose by 30 \text{%}

What is the typical range for metabolic clearance ($Clm$) of digoxin?

$0.57$ to $0.86\text{ mL/kg/min}$

How is renal clearance ($Clr$) usually related to creatinine clearance ($Clcr$) for digoxin?

$$Clr = Clcr$$

In the load dose formula, what does ‘C’ represent?

Target serum level

In the maintenance dose formula, what does ‘Css avg’ represent?

Steady state plasma level

What does ‘T’ (tau) represent in the digoxin maintenance dose formula, and what is its usual value?

Dosing interval; usually $1\text{ day}$

When is the earliest a digoxin level should be drawn after the last dose?

At least $6 - 8\text{ hours}$ after the dose

What is the optimal window for drawing a digoxin level after a dose?

$12 - 24\text{ hours}$ after the dose

If no loading dose is given, when should a digoxin sample be drawn?

After $3 - 5\text{ days}$ of therapy

If a loading dose is given, when should the sample be drawn to determine the relationship between concentration and response?

Within $12 - 24\text{ hours}$

Loading doses of digoxin are usually reserved for which patient population?

Atrial fibrillation ($AF$) patients (not used for $HF$)