Trimethoprim-sulfadiazine in the horse: serum, synovial, peritoneal, and urine concentrations after single-dose intravenous administration.

This study examines the concentration of the drugs trimethoprim (TMP) and sulfadiazine (SDZ) in the serum, synovial, peritoneal, and urine of healthy adult horses following a single injection. The research seeks to understand the distribution and elimination of these drugs in different body fluids over a 48-hour period.

Study Design

• Six healthy adult mares were selected for the study.
• Each horse was given a single intravenous injection of trimethoprim-sulfadiazine (TMP-SDZ) at a dosage rate of 2.5 mg of TMP per kg of body weight and 12.5 mg of SDZ per kg.
• Serial measurements of TMP-SDZ concentration were taken in four different body fluids (serum, synovial, peritoneal, and urine) over a 48-hour period.

Results

• The highest mean concentrations of TMP and SDZ were found in the first sample (0.5 hour) of serum, synovial fluid, and peritoneal fluid.
• The mean peak concentrations of TMP and SDZ were 4.37 micrograms/ml and 21.81 micrograms/ml for serum, 2.95 micrograms/ml and 15.31 micrograms/ml for synovial fluid, and 3.88 micrograms/ml and 19.52 micrograms/ml for peritoneal fluid.
• Urine concentrations of the drugs were high and peaked early, suggesting rapid excretion.

Elimination and Distribution

• The average elimination rates for TMP and SDZ were 0.41 and 0.26 hour-1 respectively, indicating how quickly the drugs were removed from the body.
• The elimination half-lives of TMP and SDZ were 1.91 and 2.71 hours respectively. This means that after these time intervals, half of the original drug dosage would still be present in the body.
• The volume of distribution averaged 0.59 L/kg and 0.52 L/kg for TMP and SDZ, respectively. This measure indicates the extent to which a drug is distributed in the body tissues.