Plasma protein binding and interaction studies with piroxicam

Area of Science:

• Pharmacology
• Biochemistry

Background:

• Non-steroidal anti-rheumatic drugs (NSAIDs) like piroxicam are widely used.
• Understanding drug binding to plasma proteins, particularly albumin, is crucial for predicting drug efficacy and toxicity.
• Piroxicam's interaction with human serum albumin (HSA) and plasma components requires detailed investigation.

Purpose of the Study:

• To investigate the binding characteristics of piroxicam to human serum albumin (HSA), plasma, and serum.
• To determine the binding parameters of piroxicam using the Scatchard model.
• To assess the displacement of piroxicam from HSA and plasma by various endogenous and exogenous substances.

Main Methods:

• Equilibrium dialysis was employed to study piroxicam binding at 22°C and pH 7.4.
• Scatchard analysis was used to quantify binding parameters (number of binding sites and affinity constants).
• Displacement studies were conducted using therapeutic and supra-therapeutic concentrations of potential competing substances.

Main Results:

• Piroxicam exhibits similar binding parameters to HSA, plasma, and serum, indicating albumin as the primary binding protein.
• High concentrations of salicylic acid and palmitic acid significantly increased free piroxicam levels, suggesting competitive binding.
• Other tested substances, including diazepam and bilirubin, showed minimal displacement of piroxicam at clinically relevant concentrations.

Conclusions:

• Piroxicam's binding to human plasma is predominantly mediated by albumin.
• Salicylic acid and palmitic acid possess the potential to displace piroxicam from its binding sites on albumin, which may have clinical implications.
• The high-affinity binding site for piroxicam appears similar to that of warfarin.