THE ELUTION AND BINDING CHARACTERISTICS OF RIFAMPICIN FOR 3 COMMERCIALLY AVAILABLE PROTEIN-SEALED VASCULAR GRAFTS

Rifampicin was absorbed onto gelatin-sealed (Gelsoft and Unigraft) or collagen-sealed (Hemashield) vascular grafts by soaking for 15 min in a 1000 mg/L solution. Bound drug was then eluted from the grafts by in cubation in phosphate buffered saline (PBS) at 37 degrees C and at lim ed intervals the concentration of rifampicin remaining in the grafts w as determined. Although all three grafts contained high concentrations of rifampicin immediately after absorption of drug, rifampicin concen trations rapidly fell during elution with PBS to approximately 1.25 mg /kg of graft after 5 h incubation in PBS, indicating that most of the rifampicin absorbed to the grafts was only loosely bound. However, onc e this loosely bound fraction had been removed there was a much slower elution of the remaining rifampicin from the grafts, suggesting a sec ond and much more tightly bound fraction. The tightly bound fraction e luted with an apparent half-life of 47-76 h, depending on the graft, a nd extrapolation back to time zero from this phase suggests that only a very small amount of the rifampicin is tightly bound to the graft af ter initial soaking (0.6-1.3 mg/kg).