Converted by aromatic L-amino acid decarboxylase (AADC) to dopamine

Class

Dopamine precursor (levodopa), 98% levodopa / 2% L-leucine dry-powder formulation delivered via the Cyclops dry powder inhaler for rapid rescue treatment of OFF episodes

Pathway

Striatal dopamine replacement; inhaled route achieves peak plasma concentration within ~10 minutes for rapid OFF-episode relief

Notes

original target text: Converted by aromatic L-amino acid decarboxylase (AADC) to dopamine; replenished dopamine acts on striatal D1/D2 dopamine receptors

This mechanism describes levodopa, the metabolic precursor of dopamine, used to treat Parkinson's disease, a neurodegenerative disorder marked by progressive loss of dopamine-producing neurons in the substantia nigra. Because dopamine itself cannot cross the blood-brain barrier, patients are given levodopa, an amino acid that can enter the brain and is then converted into dopamine by the enzyme aromatic L-amino acid decarboxylase (AADC). The resulting dopamine acts on striatal D1 and D2 receptors, restoring signaling in brain circuits that control movement initiation and smoothness. Over the course of chronic oral therapy, patients often experience 'OFF episodes,' periods when motor symptoms such as rigidity and slowness abruptly return as drug levels dip between doses. Because oral absorption of levodopa can be slow or unpredictable, alternative routes of delivery, such as inhalation, have been explored as a way to raise brain dopamine levels quickly and provide rescue relief during these episodes. Formulating levodopa as a dry powder combined with an inert carrier amino acid is one approach designed to enable rapid pulmonary absorption. This general strategy, precursor replacement rather than direct receptor stimulation, remains a foundational and broadly used approach across dopamine-replacement therapy in movement disorders.