The elution and binding characteristics of rifampicin for three 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 incubation in phosphate buffered saline (PBS) at 37 degrees C and at timed intervals the concentration of rifampicin remaining in the grafts was determined. Although all three grafts contained high concentrations of rifampicin immediately after absorption of drug, rifampicin concentrations 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, once this loosely bound fraction had been removed there was a much slower elution of the remaining rifampicin from the grafts, suggesting a second and much more tightly bound fraction. The tightly bound fraction eluted with an apparent half-life of 47-76 h, depending on the graft, and extrapolation back to time zero from this phase suggests that only a very small amount of the rifampicin is tightly bound to the graft after initial soaking (0.6-1.3 mg/kg).