Study Objective. To evaluate the bias and precision of three methods of measuring glomerular filtration rate (GFR) relative to a standard method.Design. Prospective, outpatient study.Setting. University-affiliated general clinical research center.Patients. Twenty-six patients with various degrees of renal function (GFR range 25-151 ml/min/1.73 m(2)).Interventions. Each patient received iothalamate twice during the study visit, first as a bolus injection and then as a priming dose followed by a constant-rate infusion for 2.5 hours.Measurements and Main Results. Plasma (Clp(IVB)) and renal clearances (Clr(IVB)) after bolus injection and plasma clearance during constant-rate infusion (Clp(INF)) were compared with standard renal clearance during constant-rate infusion (Clr(INF)). All three measures were highly correlated with Clr(INF) (r>0.90, p<0.001). The mean Clr(IVB) was not significantly different from Clr(INF) (106.3 +/- 30.4 vs 104.2 +/- 28.5 ml/min/1.73 m(2)) and provided a precise (8.8%, 95% CI 6.5-11.1%) and unbiased measure of GFR. Both Clp(IVB) and Clp(INF) were positively biased; values exceeded Clr(INF) by 11.8 +/- 11.1 (p=0.0001) and 10.5 +/- 12.5 ml/min/1.73 m(2) (p=0.0003), respectively. Use of a nonrenal correction factor of 9.8 and 10.5 ml/min/1.73 m(2) for infusion and bolus plasma clearance values, respectively, eliminated bias and improved the precision of these methods.Conclusions. Iothalamate renal clearance after bolus injection is a simple, accurate, and precise measurement of GFR and may be a useful alternative to the standard infusion method in clinical investigations. The corrected plasma clearance provides a simple index of GFR for clinical practice.

OBJECTIVE: To report the disposition of foscarnet in a patient undergoing peritoneal dialysis,CASE SUMMARY: A 34-year-old man with AIDS received foscarnet for the treatment of esophageal cytomegalovirus. We characterized the clearance of foscarnet in this patient during continuous cyclic peritoneal dialysis (CCPD) and continuous ambulatory peritoneal dialysis (CAPD).DISCUSSION: The foscarnet half-lives during CCPD and CAPD were 41.4 and 45.8 hours, respectively. These values are significantly greater than the half-life of 4.5 hours observed in patients with normal renal function and about half that reported in anuric patients undergoing hemodialysis during the interdialytic period, The CCPD and CAPD clearances of foscarnet were 5.8 and 4.5 mL/min, respectively; the CAPD clearances of creatinine and urea nitrogen were 4.1 and 6.0 mL/min, respectively. The patient's estimated total body clearance values of foscarnet during CCPD and CAPD were 9.8 and 8.8 mL/min, respectively, Thus, CCPD and CAPD augmented the patient's residual clearance of foscarnet by 145% and 105%, respectively,CONCLUSIONS: Since incremental increases in residual clearance of 30% or more generally will result in clinically significant changes in a drug's serum concentration, foscarnet dosage needs to be individualized for patients receiving peritoneal dialysis.