Determination of Furosemide in Blood Plasma and its Binding to Proteins in Normal Plasma and in Plasma from Patients with Acute Renal Failure

Abstract

A modification of the Hajdu & Häussler method (1964) for the determination of furosemide is described. The sensitivity is 10±2 ng/ml. The binding of furosemide to plasma proteins is determined in vitro at room temperature by an ultrafiltration method. At concentrations between 10 and 400 μg/ml, 99‐95% was bound in normal plasma. In therapeutically dialysed plasma from surgical patients with acute renal failure the binding was reduced by 9‐14%. The number of μg of drug bound per mg albumin was also significantly reduced in the patient plasma. A “K av1 value” for the range 10‐100 μg/ml was approximately 3 × 10 5 in donor plasma and 2 × 10 4 in patient plasma. A “k av2 value” (100‐400 μg/ml) was 3 × 10 4 in donors and 8 × 10 3 in patients. The k av1 and k av2 values were significantly lower in patient plasma than in donor plasma and also lower in patient plasma than in Ringer solutions to which albumin had been added.