18 Dec Is cavitation in autoinjectors harmful to the drug product?
Pharmaceutical industry focuses on developing prefilled syringe and autoinjector (AI) products by expanding features and capabilities. However, most of them might not be aware of an undesired phenomenon that may occur during drug solution injection called cavitation collapse. Cavitation is a phenomenon in which rapid changes of pressure in a liquid lead to the formation of small vapor-filled cavities, which upon collapsing, can generate an intense shock wave that may damage the device container and the protein drug molecules. Cavitation occurs in the syringe of the AI because of the syringe-drug relative displacement as a result of the syringe’s sudden acceleration and the ensuing pressure drop at the bottom of the container. Our high-speed video imaging visualizations show the occurrence of cavitation in many tested spring-driven AIs on the market. Therefore, it’s crucial to assess the potential damage of cavitation collapse on biomolecule drugs, syringes, and silicone oil lubricant coated on the inside of the syringe barrel.
We present the first detailed analysis of cavitation occurrence in AIs due to the sudden syringe acceleration. Effects of syringe and autoinjectors design parameters such as drive spring force, air gap size, fluid column height, and fluid viscosity on the cavitation intensity are investigated. In addition, the effects of preexisting air bubbles in the syringes on the severity of cavitation are analyzed and a cavitation intensity map is presented to show the most probable locations for severe cavitation in an autoinjector. The results indicate that larger drive spring force generates stronger cavitation since they generate higher syringe acceleration during the insertion stage, corresponding to a higher pressure drop at the bottom of the syringe, and the most severe cavitation occurrs in a syringe with a smaller air gap size. Moreover, the probability of cavitation occurrence in smaller fluid column height is significantly smaller than the larger column height, and the corresponding cavitation intensity in terms of induced extension rate is one order of magnitude lower. Also, for each configuration of the autoinjector, less severe cavitation occurrs in the syringes filled with more viscous fluid.