Technology & Development

Technology & Development

Unique local injection technology

Synartro develops local injection treatments using a patented local injection technology that enables a sustained drug release. By locally injecting the treatment, a very low dose of the active substance is needed. For other indications where local slow release of compounds with systemic safety concerns is beneficial, our technology could provide significant improvement.  

Lead program, SYN321

Drug candidate SYN321 is an intraarticular injection in development for the treatment of symptomatic knee OA. It is the slow release of diclofenac inside the joint that enables therapeutic benefits of SYN321 such as reduced side effects, prolonged pain relief as well as reduction of inflammation and pain. Further, SYN321 will also provide lubrication to the joint.

SYN321 has the potential to become the preferred second line treatment for knee OA.

Preclinical development

In the preclinical stage of SYN321 a study in horses at the Swedish University of Agricultural Sciences (SLU) compared SYN321 joint injections to a mixture of unbound hyaluronic acid and diclofenac. Diclofenac remained in the joint 10 times longer with SYN321 than with the unbound version. Minimal systemic exposure (plasma and urine) was observed, demonstrating excellent tolerability and favorable pharmacokinetics. You can find the publication here.

Efficacy for SYN321 was confirmed in an in vitro miniaturized model of human OA cartilage on a chip (uKnee®), in collaboration with BiomimX. The study revealed that SYN321 decreased the OA inflammatory response, slowed matrix-degrading events, and importantly, caused no damage to the cartilage.

The preclinical program also involved various GLP-Tox studies, which demonstrated favorable safety and local tolerability. Other steps that have been performed are manufacturing the substance under Good Manufacturing Practice (GMP).


The next step for SYN321 is a first-in-human trial in osteoarthritis patients (phase 1/2a). This trial will focus on safety and exploratory efficacy of SYN321, but will also provide indicative efficacy data. Synartro plans to manufacture trial product and start the clinical trial in 2024. The clinical trial approval was received in 2023.


The patent filed by Synartro in 2015 was initially approved in the US in May 2020, in Europe in 2021 and Canada in 2022. The patent is a compound patent, covering the unique platform of hyaluronan and a linker, that can be connected to different pharmaceutical active substances. Thus, the patent protects not only SYN321, but also other compounds based on the platform.

The patent is valid until 2035, with a possible extension of five years. It is the company’s assessment that the patent provides strong immaterial protection. Two PCT applications for the manufacturing method were filed in 2023.