Digoxin pharmacokinetics, bioavailability, efficacy, and dosage regimens in the horse.

The research investigates the pharmacokinetics, bioavailability, and efficacy of digoxin—an iv and intragastrically administered medicine—in horses, and proposes an optimal dosage regimen.

Research Methodology

• This study involved the exploration of the pharmacokinetics, or how a drug moves within an animal body, of digoxin, a drug used for various cardiac conditions.
• Digoxin was administered intravenously (directly into the bloodstream) and intragastrically (via the stomach) to six clinically normal adult horses.
• The results were measured using a radioimmunoassay, a test that uses an antibody and a radiolabeled substance to detect and measure concentrations of the drug in the horses’ blood.
• Researchers also assessed the effect of sequential injections of digoxin noting the change on a left ventricular index of contractility, which is a measure of heart functionality.

Study Findings

• After the IV injection, the dissolution process of the drug in the horse’s body followed the triexponential model—a model proposing three phases of diminishing rates of elimination.
• These three phases included a rapid distributive phase with a half-life of 15 minutes, a slow distributive phase with a half life of 4.1 hours, and a biological disposition half life of about 23.1 hours.
• The average bioavailability, the portion of the drug that enters the horse’s circulation to produce an active effect, of intragastrically administered digoxin was observed to be 19.2%.
• The highest efficacy of IV digoxin was visible in the change of the left ventricular index after the first two injections. These results showed promise for the efficacy of digoxin in treating cardiovascular issues in horses.

Proposed Digoxin Dosage for Horses

• Based on the findings of the study, the researchers proposed a specific dosage regimen for digoxin in horses: IV loading (initial dose to quickly achieve the therapeutic level) of 14, IV maintenance (dose to maintain the therapeutic level) of 7, oral loading of 70, and oral maintenance of 35 micrograms/kg/24 hours.
• Plasma digoxin concentrations measured 12 and 24 hours after administration were within the proposed therapeutic range of 0.5 to 2.0 ng/ml reinforcing that these doses are therapeutic and nontoxic.