Background:  Tenofovir (TFV) and the co-formulated product, emtricitabine/tenofovir (FTC/TFV) require dose adjustment for patients with renal impairment. We examined adherence of Veterans Health Administration (VA) prescribers to Food and Drug Administration (FDA) -approved recommendations for renal dosing for these 2 products.

Methods:  Veterans who filled an outpatient prescription for TFV or FTC/TFV during 2004 or 2005 were identified from the VA’s national Clinical Case Registry. To measure prescribed dose, we coded units per dose and dosing interval from the SIG (dosage interval) for each prescription and calculated total daily dose from these measures. To determine recommended dose, we:  estimated creatinine clearance (CrCle) using the Cockcroft-Gault algorithm with ideal weight and the result of the serum creatinine test drawn on or most closely preceding the fill date; and identified receipt of dialysis from the SIG and diagnosis and procedure codes dated within 30 days of the fill date. We compared prescribed and recommended dose and calculated descriptive statistics, overall and by level of renal impairment.

Results:  More than 9700 veterans filled over 120,000 VA prescriptions for TFV or FTC/TFV during 2004 or 2005. About 4300 of these prescriptions (3.6%) were filled by veterans whose CrCle was below 50 mL/minute, of which 309 were filled by veterans documented as receiving dialysis. About 88% of fills by those receiving dialysis were for the recommended total daily dose; however, that was the case for only 21% of fills for other veterans with CrCle <50 mL/minute. Almost all of the difference between prescribed and recommended total daily dose related to errors in dosing interval. Overall, about 7% of the 9700 veterans filled at least 1 prescription during 2004 or 2005 that was inconsistent with the dosing recommendation.

Conclusions:  Normal adult dosing is indicated for the great majority (96%) of veterans who fill a TFV or FTC/TFV prescription. However, unless they are receiving dialysis, veterans who require renal dosing usually are not prescribed the recommended dose. Efforts should be made to educate prescribers on dosing these 2 products and other antiretroviral products that require dose adjustment for patients with renal impairment, and tools should be made available to assist prescribers to readily identify patients who require renal dosing.