Predicting tenofovir concentration on the basis of renal factors determined by routine tests.

Although it has not caused overt renal damage in clinical trials, tenofovir disoproxil fumarate (TDF) has been associated with renal dysfunction in isolated cases. The objective of this study was to assess the TDF concentration with use of the glomerular filtration rate (GFR) and blood urea nitrogen (BUN) level. Serum creatinine (used to calculate GFR), BUN, and plasma TDF trough values were measured in 51 patient volunteers at pretreatment and post-treatment time points. The post-treatment GFR (post_GFR) and the difference between the pretreatment and post-treatment BUN levels (dir_BUN) were strongly related to TDF concentration. A piecewise multiple regression technique was applied to the nonlinear TDF distribution, revealing a significant association of the post_GFR and dif_BUN values with TDF concentration (P = 0.002 and P = 0.003, respectively). Post_GFR values below 125 mL/min/1.73 m 2 and/or dif_BUN values below -3 mg/dL are predicted to cause a marked increase in the TDF concentration. The relationship between TDF and BUN is a new finding. Knowledge of the pretreatment and post-treatment serum creatinine and BUN levels is important for the safe clinical administration of TDF.