Plasma DOPA response to levodopa administration in man: Effects of a peripheral decarboxylase inhibitor

Plasma DOPA leveLy were determined in depressed patients at various times after oral administration of levodopa with and without a peripheral decarboxylase inhibitor, D,L‐alpha‐methyl‐dopa‐hydrazine (MK‐485). Pretreatment with MK‐485 caused an approximately tenfold increase in the peak plasma leveLs following a DOPA load. Equivalent plasma levels were achieved with 1/10 the dose of levodopa with use of MK‐485. A significant prolongation of the half‐life of the amino acid in the plasma was aLYo achieved. The increase of plasma DOPA leveLs with MK‐485 is in the same range as the potentiation of clinical effect with this inhibitor.