Elimination of guanfacine in patients with normal and impaired renal function.

1. Total body clearance and renal clearance after single intravenous doses of guanfacine were 360 +/- 262 (mean +/- s.d.) and 233 +/- 245 ml/min, respectively, in patients with normal renal function (glomerular filtration rate (GFR) > 90 ml/min), 308 +/- 274 and 34 +/- 22 ml/min, respectively, in patients with moderately impaired renal function (GFR 30-10 ml/min), and 257 +/- 187 and 18 +/- 15 ml/min, respectively, in preuremic patients (GFR < 10 ml/min). 2. The cumulative urinary excretion up to 48 h after a single intravenous injection of guanfacine was 57.0 +/- 32.0% in patients with GFR > 90 ml/min, 14.0 +/- 9.0% in patients with GFR 30-10 ml/min and 7.5 +/- 2.4% in preuremic patients. 3. In normal as well as impaired renal function the elimination rate constant of guanfacine was 0.05 h-1, which corresponds to an elimination half-life of 14 h, independent of renal function. 4. These results suggest that non-renal elimination of guanfacine plays an important role in patients with renal failure. 5. Intestinal absorption of guanfacine was calculated to be 59 +/- 19% in patients with GFR > 90 ml/min, to 68 +/- 16% in patients with GFR 30-10 ml/min, and to 73 +/- 36% in preuremic patients.