Plasma concentrations, plasma protein binding and residues of sulfamonomethoxine in pigs, horses and cattle.

This research investigates the protein binding, plasma half-life, and residue depletion of a drug called sulfamonomethoxine (SMM) in pigs, horses, and cattle after it has been administered intramuscularly. It found that while the protein binding is weakly dependent on concentration, the plasma half-life and drug retention in tissues differs across the three species.

Protein Binding and Plasma Half-Life

• The study explores the affinity of SMM for proteins in the blood of pigs, horses, and cattle. It discovered that the degree of protein binding was concentration-dependent but weakly so, meaning that as the concentration of the drug increases, so does its protein binding ability, but not drastically.
• The bound fraction of SMM in plasma was found to be within the therapeutic range for all three animals, approximately 45% in pigs, 40% in horses, and 50% in cattle.
• The researchers also examined the plasma half-life, or the time it takes for the drug’s concentration in the blood plasma to halve after entering the body, of SMM in these animals. This was measured at approximately 5.1 hours in pigs, 5.7 hours in horses, and 3.1 hours in cattle.

Residue Depletion

• The investigation then shifted to the retention of SMM in various animal tissues. The study measured the amount of drug that remains in muscle, kidney, and liver tissues over time.
• The level of SMM in muscle tissue was found to drop below 1 microgram per gram after 36 hours in pigs, 20 hours in horses, and 12 hours in cattle.
• In kidney tissue, the SMM levels were still not less than 1 micro-gram per gram after 48 hours in pigs, 60 hours in horses, and 36 hours in cattle. This suggests that the drug is cleared from muscle tissues faster than from kidney tissues.
• It was also discovered that SMM retention at the injection site was highly variable in pigs and horses but was more regular and predictable in cattle.
• In the studied animals, the drug concentrations in the liver remained more or less constant towards the later part of the study’s investigation time, suggesting the reduction rate in the liver is slower compared to other tissues.