Lontophoretic administration of dexamethasone into the tarsocrural joint in horses.

The research examined whether iontophoretic administration (using electricity to drive medication into the body) of the drug dexamethasone into a certain joint of horses resulted in detectable levels of the drug in various bodily fluids. The study concluded that this method was not an effective way of drug delivery, as the concentration of dexamethasone was less than therapeutic levels.

Methods of the Study

• The study involved six adult female horses (mares) in which the researchers administered the drug dexamethasone through a method called iontophoresis.
• Iontophoresis uses electrical current to deliver medication; in this case, the drug was administered to the tarsocrural joint of each mare.
• Two concentrations of the drug were used, 4 mg/ml and 10 mg/ml, both contained in an electrode during the 20-minute administration at 4 mA.
• The researchers collected samples of the horses’ synovial fluid (fluid found in joints), blood, and urine before the treatment and at varying time intervals afterward (0.5 hours, 4 hours, 8 hours, and 24 hours).
• All samples were then tested for dexamethasone with an enzyme-linked immunosorbent assay (ELISA) and the synovial fluid was additionally analysed with high-performance liquid chromatography.

Results

• The ELISA test, with lower and upper detection limits of 0.21 and 1.5 ng/ml respectively, was able to detect the 10 mg/ml concentration of dexamethasone in the synovial fluid of 5 horses from 0.5 to 24 hours and in the urine of 4 horses between 0.5 to 8 hours after treatment.
• The same test, however, did not detect dexamethasone in plasma. The average synovial fluid concentration of the drug was found to be 1.01 ng/ml.
• For the lower concentration of the drug at 4 mg/ml, it was only detected in the urine of 2 mares at the 0.5 and 4-hour mark post-treatment, but was not found in the synovial fluid or plasma.

Conclusions

• The researchers concluded that iontophoresis was not an effective method for delivering dexamethasone to the synovial fluid in horses, primarily because the concentration of the drug in the synovial fluid did not reach therapeutic levels.
• This could indicate a potentially diminished therapeutic effect and, thus, could lead to treatment failure or a longer recovery time, highlighting the importance of effective drug administration methods.