Bioavailability of terfenadine in man

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Abstract
Fourteen normal male subjects were given either 60 mg or 180mg of terfenadine suspension in a randomized two‐way crossover study. Peak plasma concentrations of 1.544 ± 0.726 (mean ± S.D.) ng ml−1 were obtained in 0.786 ± 0.426 h following the 60 mg dose and displayed an AUC of 11.864 ± 3.369 ng h ml−1. Whereas peak plasma concentrations of 4.519.2 ± 002ng ml−1in 1.071 ± 0.514h were obtained following the 180mg dose. The AUC following the 180 mg dose was 44.341 ± 22.041 ng h ml−1. When 60 mg of 14C terfenadine was given to six additional subjects, the peak plasma concentrations of 351.43ng equivalents per ml were obtained in 1.67 ± 0.41 h and the AUC was 2297.71 ± 310.85ng‐equivalentshml−1. This indicates that approximately 99.5 per cent of the terfenadine related material that is absorbed undergoes biotransformation. Urinary excretion of 14C accounted for 39.89 ± 5.29 per cent of the dose while 60.58 ± 2.44 per cent of the dose was recovered in the feces in twelve days. Thin‐layer chromatographic (TLC) examination of fecal extracts showed only a trace of material chromatographing with terfenadine. This may indicate that the 14C present in the feces is not due to lack of absorption.