Methyldopa kinetics before and after ingestion of methyldopa for eight weeks.

Methyldopa urine and plasma levels and urine metabolite levels were assessed following intravenous (IV) and oral (PO) methyldopa before, and after ingestion of methyldopa (500 mg) daily for eight weeks. There was no increase in (estimated) methyldopa absorption (8.4%) or renal clearance (PO 13.9%, IV 2.33%) after the eight weeks of methyldopa ingestion. However, the initial methyldopa absorption and renal clearance values in this study were higher than that in previous studies. There was an inverse relation between the initial methyldopa absorption and the change in absorption (r - 0.605) and between the initial methyldopa renal clearance and the change in renal clearance (PO r -0.874, IV r -0.891). Overall, this study did not confirm our previous studies showing induction of methyldopa absorption and renal clearance, possibly due to prior up regulation of transporter function. Consistent with methyldopa inducing drug transporters, those with low initial absorption and renal clearance values had the greatest increases.