Pharmacokinetics and pharmacodynamics of furosemide after oral administration to horses.

The study investigates the pharmacokinetics (the movement of drug within the body) and pharmacodynamics (the physiological effects of the drug) of oral administration of furosemide, a common diuretic drug for horses. The results indicate that oral administration of the drug has poor and variable availability in the system, leading to ineffective diuresis (increased production of urine) compared to intravenous administration.

Methodology and Results: Comparing Oral and Intravenous Furosemide Administration

• The experimental setup involved a randomized, crossover design to compare the effects of both oral and intravenous administration of furosemide.
• The research aimed to measure 8-hour urine volume in three groups of horses: those receiving a placebo, those given 1 mg/kg of furosemide orally, and those given the same dose intravenously.
• To determine furosemide concentration, blood samples were drawn at specific time points and analyzed using reversed-phase high-performance liquid chromatography, a method for identifying chemical compounds in a mixture.
• The results showed that the systemic (affecting the whole body) availability of furosemide administered orally was both unreliable and inconsistent across different horses, with a median systemic bioavailability (the proportion of the drug that enters circulation) of just 5.4%.

Insufficient Diuresis Effect of Oral Furosemide Administration

• Horses that were administered the drug intravenously were found to produce significantly more urine over an eight-hour period than horses administered the drug orally.
• The maximum plasma concentration (how much of the drug is in the bloodstream) of 0.03 micrograms/mL achieved through oral administration did not lead to an increase in urine production compared to the control sample (horses without any administered drug).
• A mild decrease in urine specific gravity—a measure of urine concentration—occurred within 1-2 hours following oral administration, although the specific gravity was lower in horses given oral furosemide compared to the control at the 2-hour mark.

Ineffective Results and Conclusion

• Despite these observations, the systemic availability remained poor and inconsistent.
• The study concluded that administering furosemide orally at a dose of 1 mg/kg does not induce diuresis in horses, highlighting the inefficiency of oral administration.