Letter to the Editor
To the Editor:
We thank Campbell et al for their evaluation of our hypothesis that tenofovir-related nephrotoxicity is not always fully reversible. They correctly note that we did not report the rate of decline in estimated glomerular filtration rate (eGFR) before initiation of tenofovir. They state that tenofovir-related nephrotoxicity is reversible because the decline in eGFR in those who developed chronic kidney disease (eGFR <60 mL min−1·1.73 m−2 for at least 3 months) was similar before tenofovir initiation and after tenofovir cessation (−2.3 mL min−1·1.73 m−2 per year and −2.2 mL min−1·1.73 m−2 per year, respectively).
However, the rate of change after tenofovir discontinuation will be the sum of the rate due to pre-existing renal disease and of the rate of recovery from tenofovir toxicity. If tenofovir-related nephrotoxicity were reversible, the rate of change after tenofovir cessation must be less (ie, more positive) than the rate before cessation, as the underlying rate of decline associated with pre-existing renal disease would necessarily be lessened by any increase in eGFR after tenofovir cessation. For example, if eGFR declined by 2.3 mL min−1·1.73 m−2 per year before tenofovir, then declined by 8 mL min−1·1.73 m−2 per year on tenofovir and then fully reversed, then the rate of change after tenofovir cessation would be about +5.73 mL min−1·1.73 m−2 per year. The similar rates before and after tenofovir therapy in the population described by Campbell et al suggest that tenofovir nephrotoxicity was, as in our patients, also not reversible in those who developed chronic kidney disease.
Our interpretation of these new data is that tenofovir nephrotoxicity does not progress when tenofovir is stopped but that tenofovir nephrotoxicity is not fully reversible.
Andrew Carr, MBBS, MD, FRACP, FRCPA
HIV, Immunology and Infectious Diseases Unit and Head, Clinical Research Program Centre for Applied Medical Research St Vincent's Hospital Professor of Medicine University of New South Wales Sydney, Australia