Strategies for Treating Motor Fluctuations in Parkinson’s Disease

Future Therapies Undergoing Trials Today

Several new therapeutic approaches have been developed for dealing with the shortcomings of current therapies, especially levodopa. “The first of these options was a tube inserted through the stomach into the upper small intestine for continuous pumping of a carbidopa-levodopa microsuspension gel –quite effective but not an easy choice for most patients,” said Dr. LeWitt. Less cumbersome ways to extend levodopa effects have been the several sustained-release formulations now under development. One is a gastric-retention product, termed the “Accordion Pill,” which slowly leaches carbidopa and levodopa to enhance their pharmacokinetic absorption profile. Another treatment strategy for motor fluctuations that, like the Accordion Pill, is also in worldwide clinical trials, involves continuous subcutaneous infusion of solubilized levodopa and carbidopa. With the latter approach, the drug is administered by a small pump adjusted to optimized rate of delivery. Dr. LeWitt also described another novel way for administering levodopa for rapid entry into the bloodstream for treating “off” states. This involves an inhalation device for pulmonary uptake of a micro-particulate levodopa formulation. In a recently completed study, “off” states were reversed rapidly with this approach.

Subcutaneous apomorphine infusion has already been used for more than 30 years in treating motor fluctuations. However, just recently, a more complete story of what this adjunctive therapy offers was reported from a large-scale randomized clinical trial in Europe. A similar study is underway in the United States and might lead to availability of apomorphine infusion in the near future, said Dr. LeWitt. Another approach to motor fluctuations can be found in a drug for motor fluctuations that does not act on dopaminergic pathways. This medication is istradefylline, a selective inhibitor of adenosine A2a receptors (which are located in the same pathway targeted by deep brain stimulation). In Japan, istradefylline is marketed for reducing “off” time, and studies with this drug are planned for review in the US, said Dr. LeWitt.

For a nonpharmacologic approach to managing motor fluctuations, neurosurgical targeting of brain circuitry with deep brain electrical stimulation has had several decades of experience. Another direction of neurosurgical intervention is under investigation; this involves gene therapy to improve the efficacy of oral levodopa therapy. “Inserting into the putamen a gene for producing an increase of L-aromatic amino acid decarboxylase appears to offer a way for enhancing dopamine formation. The clinical investigation currently underway is testing whether producing this localized alteration of brain neurochemistry might succeed at attenuating motor fluctuations,” said Dr. LeWitt

“In talking to patients about their experiences with motor fluctuations, my advice is to think both about levodopa pharmacokinetics and how the patient uses levodopa (since schedule compliance, the interaction of meals, and drinking sufficient water with medications commonly contribute to these problems). Fortunately, new treatment options are on their way to help in fighting back against the limitations of levodopa therapy,” Dr. LeWitt concluded.

—Erica Tricarico

Suggested Reading

Anderson E, Nutt J. The long-duration response to levodopa: phenomenology, potential mechanisms and clinical implications. Parkinsonism Relat Disord. 2011;17:587-592.

Cilia R, Akpalu A, Sarfo FS, et al. The modern pre-levodopa era of Parkinson’s disease: insights into motor complications from sub-Saharan Africa. Brain. 2014;137(10);2731-2742.

LeWitt PA. Levodopa therapy for Parkinson’s disease: Pharmacokinetics and pharmacodynamics. Mov Disord. 2015;30(1):64-72.