A pulmonary formulation of L-dopa enhances its effectiveness in a rat model of Parkinson's disease

The efficacy of oral L-dopa becomes problematic with the progression of Parkinson's disease, due in large part to a lost ability to accommodate L-dopa's inherently poor pharmacokinetics. Pulmonary delivery represents a novel approach to reducing this problem. L-dopa was formulated into inhalable (Alkermes AIR) particles, and its pharmacokinetics and pharmacodynamics compared with those of an oral formulation. Pulmonary administration of L-dopa (2 mg) to rats resulted in a rapid elevation of plasma levels (C-max = 4.8 +/- 1.10 mug/ml at 2 min), whereas oral administration of L-dopa produced a much delayed and lower C-max (1.8 +/- 0.40 mug/ml at 30 min). In a rat model of Parkinson's disease (unilateral 6-hydroxydopamine lesion), the pulmonary formulation of L-dopa (0.5-2.0 mg) yielded more rapid and robust elevations in striatal L-dopa, dopamine, and dihydroxyphenylacetic acid levels, as well as 2.5 to 3.7 times as many c-fos-expressing striatal neurons. Moreover, motor function was significantly improved by 10 min after administration, with peak improvements occurring within 15 to 30 min. In contrast, considerably higher doses (6.8-10 mg) of orally administered L-dopa took over three times longer to produce similar effects. These results suggest that an inhalable formulation of L-dopa has superior pharmacokinetic properties and may provide patients with a more effective form of rescue therapy as well as being a reliable adjuvant or replacement for first-line oral therapy.