Digoxin disposition kinetics in dogs before and during azotemia

Area of Science:

• Pharmacokinetics
• Veterinary Medicine
• Nephrology

Background:

• Digoxin is a cardiac glycoside used to treat heart failure.
• Azotemia, a condition of elevated nitrogenous waste products in the blood, can affect drug metabolism and excretion.
• Understanding digoxin disposition in azotemic conditions is crucial for safe and effective therapeutic use in dogs.

Purpose of the Study:

• To investigate the disposition kinetics of digoxin in dogs before and during experimentally induced azotemia.
• To quantify changes in digoxin's half-life, clearance, and volume of distribution under azotemic conditions.

Main Methods:

• Single intravenous dose administration of digoxin to the same dogs in a pre-azotemic and azotemic state.
• Analysis of digoxin plasma concentration-time data using multicompartment modeling and nonlinear regression.
• Calculation of pharmacokinetic parameters including biological half-life, renal clearance, body clearance, and apparent volume of distribution.

Main Results:

• Azotemia significantly prolonged the biological half-life of digoxin in 6 out of 7 dogs.
• Digoxin renal clearance, body clearance, and apparent volume of distribution were significantly decreased during azotemia.
• A substantial nonrenal elimination pathway for digoxin was identified, accounting for approximately 45% of the dose, which remained unchanged during azotemia.

Conclusions:

• Azotemia markedly alters digoxin disposition kinetics in dogs, leading to reduced drug clearance and prolonged half-life.
• The significant nonrenal elimination component of digoxin in dogs plays a critical role in its overall elimination, especially when renal function is compromised.
• These findings highlight the need for careful digoxin dosage adjustments in azotemic canine patients to avoid toxicity.