Scientists from the University of South Australia (UniSA) have developed a long-acting injectable formulation that delivers a steady dose of levodopa and carbidopa - two key medications for Parkinson's - over an entire week.

Their findings have been reported in the journal Drug Delivery and Translational Research.

The biodegradable formulation is injected under the skin or into muscle tissue, where it gradually releases the medication over seven days.

Parkinson's disease is the second most common neurological disorder, affecting more than 8.5 million people worldwide. Currently there is no cure and the symptoms - tremors, rigidity and slow movement - are managed with oral medications that must be taken several times a day.

The frequent dosing is a burden, especially for elderly patients or those with swallowing difficulties, leading to inconsistent medication levels, more side effects, and reduced effectiveness.

Lead researcher Professor Sanjay Garg, from UniSA's Centre for Pharmaceutical Innovation, says the newly developed injectable could significantly improve treatment outcomes and patient adherence.

"Our goal was to create a formulation that simplifies treatment, improves patient compliance, and maintains consistent therapeutic levels of medication. This weekly injection could be a game-changer for Parkinson's care," Prof Garg says.

"Levodopa is the gold-standard therapy for Parkinson's, but its short life span means it must be taken several times a day."

UniSA PhD student Deepa Nakmode says the in-situ implant is designed to release both levodopa and carbidopa steadily over one week, maintaining consistent plasma levels and reducing the risks associated with fluctuating drug concentrations.

"After years of focused research, it's incredibly rewarding to see our innovation in long-acting injectables for Parkinson's disease reach this stage. Our invention has now been filed for an Australian patent," Nakmode says.

The injectable gel combines an FDA-approved biodegradable polymer PLGA with Eudragit L-100, a pH-sensitive polymer, to achieve a controlled and sustained drug release.

Extensive lab tests confirmed the system's effectiveness and safety:

• More than 90% of the levodopa dose and more than 81% of the carbidopa dose was released over seven days.
• The implant degraded by over 80% within a week and showed no significant toxicity in cell viability tests.
• The formulation can be easily administered through a fine 22-gauge needle, minimising discomfort and eliminating the need for surgical implant.

"The implications of this research are profound," Prof Garg says. "By reducing the frequency of dosing from multiple times a day to a weekly injection is a major step forward in Parkinson's therapy. We're not just improving how the drug is delivered; we're improving patients' lives."

Prof Garg says the technology could also be adapted for other chronic conditions such as cancer, diabetes, neurodegenerative disorders, pain management, and chronic infections that require long-term drug delivery.

The system can be tuned to release drugs over a period ranging from a few days to several weeks depending on therapeutic needs.

UniSA scientists hope to start clinical trials in the near future and are exploring commercialisation opportunities.