Using liquid levodopa in the treatment of Parkinson's disease. A practical guide

Many patients with Parkinson's disease develop both involuntary movements from and a critical dependency on, levodopa therapy as their disease progresses. This results in a narrow therapeutic window in which blood concentrations of levodopa can achieve optimal control of parkinsonian symptoms. The short half-life of levodopa, combined with loss of intraneuronal storage capacity for levodopa as the disease progresses, results in patients experiencing marked motor fluctuations complicated by medication-induced dyskinesias. When given in tablet form, the dosage of levodopa (which is usually combined with a decarboxylase inhibitor such as carbidopa or benserazide) often cannot be titrated adequately, and the drug may become unpredictable in its ability to relieve parkinsonian symptoms. A solution of levodopa and carbidopa, stabilised using ascorbic acid, offers a means of delivering a titrated amount of levodopa at regular intervals. Solutions pass through the stomach faster than solids, affording more rapid symptomatic relief in some patients with Parkinson's disease.