Letter by Lema et al Regarding Article, “Renal Vasodilatory Action of Dopamine in Patients With Heart Failure: Magnitude of Effect and Site of Action”
To the Editor:
I have read with great interest the article by Elkayam et al1 regarding renal effects of dopamine in a group of patients with heart failure. I would like to add some comments to the discussion.
The vasodilatory effects of dopamine have been reported previously.2 A debatable “renal protection effect” has been erroneously attributed to this finding.
The study shows vasodilatory effect of dopamine, with an increase in renal blood flow measured by Doppler technique. However, the authors do not find significant differences in renal blood flow when doses greater than 2 μg · kg−1 · min−1 are infused. They discuss whether the small number of patients undergoing the study may explain this finding.
This could be true; however, there could be another explanation for this finding. In fact, an important intersubject variability on plasma levels of dopamine has been described. A study published by MacGregor et al3 showed in healthy normal subjects that the plasma concentration of dopamine varied from 12 300 to 201 500 ng/L after 10 μg · kg−1 · min−1 of dopamine. When patients received 3 μg · kg−1 · min−1, concentration varied from 1800 to 18 300 ng/L. They conclude that in a homogenous population, a dopamine dose based only on body weight may give unpredictable plasma levels and clinical effects. Compartmental pharmacokinetic models may explain this behavior (changes of dopamine distribution and metabolism).
There is no reason to think that patients such as those studied in the work by Elkayam et al1 would behave differently. Clinical effects and the variability among patients may depend on the plasma levels and its subsequent action on the different known receptors.
Source of Funding
This work was funded by grant No. FONDECYT 1030645–2003.