A Radioimmunoassay Procedure for the Determination of the Antiviral Nucleoside DHPG (9-[(l,3-Dihydroxy-2-propoxy)-methyl]guanine) in Plasma or Serum

A procedure is described that is suitable for the radioimmunoassay (RIA) of 9-(l,3-dihydroxy-2-propoxy)-methyl]guanine (DHPG) in plasma or serum at concentrations as low as 0.7 ng/ml (2.75 × 10^–9 M). Antiserum was prepared by coupling DHPG monohemisuccinate to bovine serum albumin and immunizing rabbits with the resulting conjugate. The antibodies did not show significant cross-reactivities with structurally related endogenous compounds. For RIA, tritium-labeled DHPG was used as the tracer and charcoal–dextran was used to separate the free and bound fractions. No purification of samples was required prior to RIA. The accuracy of the method was assessed by adding known quantities of DHPG to DHPG-free plasma and determining the ratio of measured to added analyte. Linear regression analysis for the concentration range 0.0007 to 15.0 µg/ml yielded the following equation; y = 0.90 x + 0.033 (r = 0.999). Additional validation was obtained from studies in which DHPG was administered to a monkey, mice, dogs, and rats, and plasma-clearance profiles were determined by RIA and high-performance liquid chromatography (HPLC). The results obtained by RIA were in good agreement with those obtained by HPLC.