A very significant percentages of ESRD patient admissions derive from clotted dialysis access–the “lifeline” dialysis patients require in order to survive on dialysis. Any maneuver or treatment which is successful in preventing, or even delaying, access thrombosis would be welcomed throughout the Nephrology community.
A recent NEJM article by Dixon et al suggests that a combination of aspirin and dipyridamole can improve access patency rates by a modest but significant amount. The study looked only at arteriovenous grafts (AV grafts), which have a higher rate of thrombosis than arteriovenous fistulas by comparison. It was a randomized control trial in which patients were randomized to either placebo or 25mg ASA/200mg extended-release dipyridamole twice daily within a day or two of successful AV graft surgery. The primary outcome here was loss of primary unassisted graft patency–that is, did the graft stay patent without requiring any intervention such as thrombectomy. One strength of the study is that graft patency was quantitatively defined in terms of changes in blood-flow rate at dialysis and/or angiographically-defined stenoses.
The most important finding of this study was that the incidence of graft patency at 1 year was 23% in the placebo group and 28% in the dipyridamole-aspirin group. Another way of expressing this data was that the addition of dipyridamole-aspirin resulted in a hazard ratio of 0.82, with a confidence level that just barely missed crossing 1 (0.68 – 0.98) . Thus, the authors claim that this treatment resulted in a modest but significant improvement in graft patency.
The decision to use dipyridamole-aspirin on a regular basis in dialysis patients with AV grafts would also have financial repercussions. The authors point out that the cost of dipyridamole-aspirin (marketed under the name Aggrenox by Boehringer Ingelheim) is between $500 – $2,200 per year per person. Of note, the manuscript also notes that although the drug company supplied drugs for the study, they were explicitly not included in the study design or analysis, as the study was sponsored primarily by the NIDDK.