Serum specific activity curves were obtained after iv and oral administration of [14C]disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP™, disodium etidronate) in 9 healthy adult males. In group I the oral carrier dose of EHDP was 5 mg/kg and in group II 30 mg/kg. Absorption in each case (percent of oral dose administered) was expressed by an inverse convolution function of the two curves solved by Laplace transforms (total percent absorption, TPA); by the oral:iv serum equilibrium ratio at 150 min; by the oral:iv urine recovery ratio (Group I) and by the fecal recovery (Group II, 100 - fecal recovery). Twenty-four-hr urine isotope recovery after iv tracer was obtained in group 1. Forty-eight hr urine recoveries after oral administration of the isotope were obtained in both groups and 5-day fecal recoveries were obtained in group II. In group I, the mean absorption by the deconvolution technique was 1.49%, by the oral:iv serum equilibrium ratio 2.95% and by the oral:iv urine recovery ratio 3.35%. Mean urine recovery after iv isotope was 52.0% and after oral isotope was 1.80%, of the administered dose. In group II mean absorption by the deconvolution technique was 3.99%, by the oral:iv serum equilibrium ratios, 7.19% and by fecal recovery values 10.2%. Urine recovery after the oral administration of the isotope averaged 3.10%, and fecal recovery (excluding one subject), 93.0% of the oral dose. Retention (100 - total recovery, excluding one subject) in group II averaged 6.9% of the oral dose. It was concluded that the best estimate of absorption in group I was the oral:iv urine recovery ratio (3.35%), and in group II the oral:iv serum equilibrium ratio at 150min (7.19%).
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