Plasma concentrations and pharmacokinetics of dihydralazine after single oral doses to human subjects

After single oral doses of 20 mg of a suspension of dihydralazine sulphate to human subjects, the peak of mean plasma concentrations of dihydralazine of 47·0 ng ml−1 ± 11·0 standard deviation (S.D.) (n = 7) was reached at 1 h. Mean concentrations declined biphasically with apparent half-lives of 0·57 and 4·96 h respectively. Dihydralazine was partly converted to hydralazine. The peak of mean plasma concentrations of the latter drug of 3·9 ng ml−1 ± 1·7 S.D. (n = 7) occurred at 1–2 h after dosing with dihydralazine sulphate and declined to 1–5 ng ml−1 ± 1·5 S.D. at 6 h. Of the seven subjects studied, three were classified as fast and four as slow acetylators. Mean clearances appeared to be slightly more rapid in fast acetylators (1·63 1 min−1 ± 0·32 S.D.) when compared to slow acetylators (1·31 1 min−1 ± 0·31 S.D.) but this difference and differences in plasma concentrations and in areas under the plasma drug concentration-time curves were not significant (p > 0·1).