Decreased plasma protein binding of diazoxide in uremia

The effect of uremia on the binding of diazoxide to plasma proteins was studied. An equilibrium dialysis technique, using diazoxide-minus14C at approximately 30 and 300 mug/ml in the plasma phase, was used to measure diazoxide binding to plasma. Serum albumin concentration (Alb) and serum creatinine (Cr) or blood urea nitrogen (BUN) were negatively correlated. By single regression analysis, per cent free diazoxide (%FD) correlated negatively with Alb and positively with Cr or BUN. When %FD was regressed simultaneously against Alb and Cr or BUN, Alb emerged as the sole determinant of %FD (p less than 0.001), indicating that creatinine or BUN correlated with %FD by their inverse correlation to Alb rather than by an effect on drug protein binding. At the levels of Alb studied, %FD varied over a 2-fold range. In a retrospective study of the influence of uremia on diazoxide effect in hypertensive patients, a relatively low correlation (r, 0.59) was found between BUN and hypotensive effect. Prospective studies involving correlations of drug effect with renal function and %FD are required to assess the clinical importance of decreased binding of diazoxide to uremic plasma.