Naproxen in the horse: pharmacokinetics and side effects in the elderly.

The research article investigates the pharmacokinetics (how a drug is absorbed, distributed, metabolized, and excreted) and side effects of the drug naproxen in older horses over a span of 5 days. The study indicates that naproxen was well-tolerated with no side effects or changes in gastric tissue observed.

Study Design and Methods

• The study was conducted on horses aged 18 years and older, the group that can often show physiological and pathological changes which can affect drug response.
• The drug, naproxen, was administered orally at a dose of 10 mg/kg body weight per day for 5 days.
• The researchers focused on various indicators to measure drug absorption and metabolism. These included the maximum concentration of the drug in the body (Cmax), the time it took to reach that concentration, the mean terminal half-life of the drug (amount of time for the concentration to drop by half), the area under the concentration-time curve (AUC), mean residence time (MRT), and the level of protein binding.

Results

• The maximum concentration of naproxen was reached approximately 2.5 hours after treatment, with the harmonic mean terminal half-life noted to be around 6.96 hours.
• The study noted an AUC of 459.71 ± 69.95 h μg/mL, indicating the total drug exposure over time, and an MRT of 7.44 ± 0.74 h, indicating the average time the drug stays in the body.
• High protein binding of 98.47 ± 2.72% was reported. Protein binding is the drug’s ability to bind to proteins in the blood, particularly albumin, and influences a drug’s pharmacokinetics.
• Interestingly, no drug accumulation occurred with repeated administrations, highlighting the body’s ability to efficiently metabolize and excrete the drug.

Safety and Side Effects

• After naproxen administration, no clinical and laboratory changes were detected, suggesting that the drug was well-tolerated in the studied horses.
• Moreover, gastric endoscopies were performed post-treatment and no pathological changes were observed in the gastric mucosa, which is a notable finding given that non-steroidal anti-inflammatory drugs (NSAIDs) like naproxen can often cause gastrointestinal side effects.