In Reply

Abstract

We appreciate Dr Diskin's review of our paper about vascular access outcomes and the use of specific drugs in the DOPPS.1Saran R. Dykstra D.M. Wolfe R.A. Gillespie B.M. Held P.J. Young E.W. Association between vascular access failure and the use of specific drugs The Dialysis Outcomes and Practice Patterns Study (DOPPS) .Am J Kidney Dis. 2002; 40: 1255-1263Abstract Full Text Full Text PDF PubMed Scopus (150) Google Scholar While our conclusions are very similar to results reported by Dr Diskin in his Letter to the Editor, major differences in methodology exist. The DOPPS is an international, multicenter study wherein outcomes and medication data are collected in a systematic, prospective manner (Dr Diskin's study was based on a retrospective chart review). We collected detailed demographic and comorbidity data (over 50 conditions) from which 12 factors were identified as significant model covariates, allowing adjustment for case-mix differences. It was unclear whether similar, adequate adjustments were made in Dr Diskin's study.2Diskin C.J. Stokes T.J. Thomas S.G. et al.An analysis of the effect of routine medications on hemodialysis vascular access survival.Nephron. 1998; 78: 365-368Crossref PubMed Scopus (21) Google Scholar While we did not have actual start or stop dates for various drugs, the interval follow-up questionnaires confirmed that patients were receiving drugs at the time of access creation and were on them for at least 4 months or, more likely, for at least 8 months. Compliance is an issue with any drug study. While coumadin may have been prescribed for prevention of vascular access thrombosis, we cannot ascertain this from our database. However, it may have been prescribed for other cardiovascular indications (chronic atrial fibrillation, mural thrombus, or stroke prevention). We emphasize the “confounding by indication” phenomenon in our paper. Despite the limitations of observational studies, our paper is the only comprehensive, statistically robust analysis dealing with use of drugs in regard to vascular access outcomes. These data, of course, do not replace randomized clinical trials. We appreciate Dr Diskin's review of our paper about vascular access outcomes and the use of specific drugs in the DOPPS.1Saran R. Dykstra D.M. Wolfe R.A. Gillespie B.M. Held P.J. Young E.W. Association between vascular access failure and the use of specific drugs The Dialysis Outcomes and Practice Patterns Study (DOPPS) .Am J Kidney Dis. 2002; 40: 1255-1263Abstract Full Text Full Text PDF PubMed Scopus (150) Google Scholar While our conclusions are very similar to results reported by Dr Diskin in his Letter to the Editor, major differences in methodology exist. The DOPPS is an international, multicenter study wherein outcomes and medication data are collected in a systematic, prospective manner (Dr Diskin's study was based on a retrospective chart review). We collected detailed demographic and comorbidity data (over 50 conditions) from which 12 factors were identified as significant model covariates, allowing adjustment for case-mix differences. It was unclear whether similar, adequate adjustments were made in Dr Diskin's study.2Diskin C.J. Stokes T.J. Thomas S.G. et al.An analysis of the effect of routine medications on hemodialysis vascular access survival.Nephron. 1998; 78: 365-368Crossref PubMed Scopus (21) Google Scholar While we did not have actual start or stop dates for various drugs, the interval follow-up questionnaires confirmed that patients were receiving drugs at the time of access creation and were on them for at least 4 months or, more likely, for at least 8 months. Compliance is an issue with any drug study. While coumadin may have been prescribed for prevention of vascular access thrombosis, we cannot ascertain this from our database. However, it may have been prescribed for other cardiovascular indications (chronic atrial fibrillation, mural thrombus, or stroke prevention). We emphasize the “confounding by indication” phenomenon in our paper. Despite the limitations of observational studies, our paper is the only comprehensive, statistically robust analysis dealing with use of drugs in regard to vascular access outcomes. These data, of course, do not replace randomized clinical trials.