Equivalent dosing of irbesartan, valsartan, and losartan identified through formulary switch at a Veterans Affairs medical center

Until 2005, irbesartan was the only ARB available on the Veterans Affairs (VA) healthcare system's national formulary. In 2005, irbesartan was removed from the formulary and was replaced with valsartan and losartan. For those patients who were to continue ARB therapy via a switch to either losartan or valsartan, dosing guidelines were created by the Veterans Integrated System Network 7 to facilitate the change. These guidelines suggested that patients taking irbesartan 150 mg once daily be treated with either valsartan 80 mg or losartan 50 mg once daily and that patients taking irbesartan 300 mg once daily be treated with either valsartan 160 mg or losartan 100 mg once daily. To determine if the dosing guidelines resulted in equal antihypertensive effectiveness, we carried out a retrospective chart review, examining the cases of 86 patients at the William Jennings Bryan Dorn VA Medical Center in Columbia, South Carolina, who had switched from irbesartan to either losartan or valsartan; 11 of these patients had been taking irbesartan 75 mg once daily and were switched to valsartan 40 mg or losartan 25 mg once daily based on an extrapolation of the guidelines. The 4 most recent consecutive blood pressure (BP) measurements before the switch were compared with the first 4 consecutive BP measurements after the switch. Additionally, the 3 most recent serum creatinine and serum potassium values before the switch were compared with the first 3 values after the switch. No statistically significant difference was observed between the BP measurements taken before and after the switch (F [3,209]=.11; P=.95). No significant changes were observed in serum potassium (P=.42) or serum creatinine (P=.71) values. Although the generalizability of these results may be limited, as the study was restricted to a small, mostly male population of veterans, we believe that the results demonstrate the therapeutic equivalence of specific doses of irbesartan, losartan, and valsartan. [PUBLICATION ABSTRACT]