Piroxicam-natural polymers interactions.
The interaction of the anti-inflammatory drug, piroxicam, with some naturally occurring polymers-viz gamma-globulin, bovine serum-albumin, bovine synovial fluid and casein was characterized in this study. This was done using equilibrium dialysis method where the dialysis membrane was permeable only to the drug molecules while polymers and formed complex(es) cannot pass through. The amount of permeable piroxicam molecules was determined spectrophotometrically. It was found out that increasing the concentration of piroxicam was accompanied by an increase in the amount of piroxicam bound to the investigated natural polymers. The maximum binding capacity of the investigated polymers for the drug as revealed by Langmuir plots, could be arranged in ascending manner as follows: synovial fluid, albumin, casein and gamma-globulin. The binding parameters K (association constant) and n (the number of binding sites available on the polymer) were determined using Sandberg plots. It was found that two classed of binding sites were involved in the interaction of piroxicam with gamma-globulin, albumin and casein. Increasing salt concentration was accompanied by a decrease in piroxicam binding with the investigated polymers till a constant value of ionic strength (0.6 mole/liter). This result may suggest the ionic nature in binding of piroxicam with the investigated polymers. It was concluded that piroxicam is strongly bound to the investigated natural polymers with different degree of binding, such binding may affect the pharmacological effect of piroxicam. An in-vivo absorption study was performed on eight male healthy volunteers to compare the bioavailability of piroxicam in presence and absence of casein using plasma data after 100 mg single dose treatment.(ABSTRACT TRUNCATED AT 250 WORDS)