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Nephrol Dial Transplant (2003) 18: 1415-1416
© 2003 European Renal Association-European Dialysis and Transplant Association
Letters and Replies
Reply
Department of Renal Medicine, King's College Hospital, London, UK Email: icm-kru{at}globalnet.co.uk
Sir,
The data from Geddes (see letter above) and Jones et al. [1] that I referred to in my recent review [2] highlight an interesting general point regarding clinical trials and everyday clinical practice. The former usually recruit a highly select population (with multiple exclusion criteria), whereas physicians in their own units have to treat all their patients, including the ones that would not have satisfied the inclusion criteria for a particular clinical trial. Extrapolating data from a clinical trial into everyday clinical practice is therefore often flawed, and such data (although often useful and enlightening) often generate more questions than answers. For example, there is now overwhelming evidence from large-scale well conducted clinical trials that lipid-lowering therapy reduces cardiovascular risk in the general population, and yet such trials usually have ‘renal failure’ as an exclusion criterion. Does this mean that the statins confer a cardiovascular benefit in chronic renal failure patients?
In terms of renal anaemia management, the best example in recent times is the US Normal Hematocrit Trial [3]. This large-scale well conducted randomized prospective controlled trial suggested that there was no massive benefit to be gained from fully correcting renal anaemia. And yet this study was conducted in high-risk cardiac patients who were receiving regular haemodialysis. Does this mean that normalizing the haemoglobin is inappropriate in a young fit peritoneal dialysis patient [4]?
The debate about once-weekly epoetin vs once-weekly darbepoetin alfa will continue, fuelled by claims from the manufacturers of the different products. The only robust scientific evidence we have is that darbepoetin alfa has a longer circulating half-life than epoetin alfa [5], and that epoetin alfa and epoetin beta have very similar half-lives [6]. As stated in my review [2], pharmacokinetic data do not necessarily predict biological response, and until a head-to-head study is conducted, we shall have to live with this uncertainty. Geddes' final comment regarding any possible difference between epoetin alfa and epoetin beta is hard to imagine in terms of the pharmacokinetic data we have [6], but again a controlled study comparing the efficacy of the two epoetins is lacking.
References
- Jones CH, Ridley L, Richardson D. Which EPO dose per week? Nephrol Dial Transplant 2002; 17:1855
[Free Full Text] - Macdougall IC. Once-weekly erythropoietic therapy: is there a difference between the available preparations? Nephrol Dial Transplant 2002; 17:2047–2051
[Free Full Text] - Besarab A, Kline Bolton W, Browne JK et al. The effects of normal as compared with low hematocrit values in patients with cardiac disease who are receiving hemodialysis and epoetin. N Engl J Med 1998; 339:584–590
[Abstract/Free Full Text] - Macdougall IC. Should the hematocrit be normalized in dialysis and in pre-ESRD patients? Blood Purif 2001; 19:157–167[Medline]
- Macdougall IC, Gray SJ, Elston O et al. Pharmacokinetics of novel erythropoiesis stimulating protein compared with epoetin alfa in dialysis patients. J Am Soc Nephrol 1999; 10:2392–2395
[Abstract/Free Full Text] - Halstenson CE, Macres M, Katz SA et al. Comparative pharmacokinetics and pharmacodynamics of epoetin alfa and epoetin beta. Clin Pharmacol Ther 1991; 50:702–712[Web of Science][Medline]
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  C. Tolman, D. Richardson, C. Bartlett, and E. Will Structured Conversion from Thrice Weekly to Weekly Erythropoietic Regimens Using a Computerized Decision-Support System: A Randomized Clinical Study J. Am. Soc. Nephrol., May 1, 2005; 16(5): 1463 - 1470. [Abstract] [Full Text] [PDF]
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