Prefilled Syringe Injection Force Impact Assessment from Back Pressure: An Approach for Testing Syringe Injectability In Situ vs. In Vitro

Prefilled syringes are commonly used combination products for parenteral drug and vaccine administration. The characterization of these devices is through functionality testing, such as injection and extrusion force performance. This testing is typically completed by measuring these forces in a nonrepresentative environment (i.e., dispensed in-air) or route of administration conditions. Although injection tissue may not always be feasible or accessible for use, questions from the health authorities make it increasingly important to understand the impact of tissue back pressure on device functionality. Particularly for injectables containing larger volumes and higher viscosities, which can widely impact injection and user experience. This work evaluates a comprehensive, safe, and cost-effective in situ testing model to characterize extrusion force while accounting for the variable range of opposing forces (i.e., back pressure) experienced by the user during injection into live tissue with a novel test configuration. Due to the variability of back pressure presented by human tissue for both subcutaneous and intramuscular injections, tissue back pressure was simulated (0 psi-13.1 psi) using a controlled, pressurized injection system. Testing was conducted across different syringe sizes (2.25 mL, 1.5 mL, and 1.0 mL) and types (Luer lock and stake needle) with two simulated drug product viscosities product (1 cP and 20 cP). Extrusion force was measured using a Texture Analyzer mechanical testing instrument with crosshead speeds of 100 mm/min and 200 mm/min. The results demonstrated that there is a contribution of increasing back pressure on extrusion force across all syringe types, viscosities, and injection speeds that can be predicted using the proposed empirical model. Moreover, this work demonstrated that the factors that largely influence the average and maximum extrusion force during injection are syringe and needle geometries, viscosity, and back pressure. This understanding of the device usability may aid in the development of more robust prefilled syringe designs to minimize use-related risks.

Optimizing ACTH-stimulated steroid secretion by cultured adrenocortical tumor cells

If 1 mM supplemental Ca++, or 1.6 mg hemoglobin (Hb)/ml medium (23.5 uM, a concentration comparable to that in 1 ml mouse blood), was added to Eagle's minimum essential medium (MEM) (which contains 1 mM Ca++), basal and maximally stimulated 20-dihydroprogesterone (20-DHP) secretion by cultured Y-1 mouse adrenal tumor cells [49-65th passages] could be measured by radioimmunoassay after a 0.5 hr incubation. ACTH-stimulated, but not basal, 20-DHP secretion increased after 1 mM Ca++ treatment. 5 mM EGTA significantly reduced basal and stimulated 20-DHP secretion, although significant ACTH stimulation still remained. Basal and stimulated secretion significantly increased when Hb was present. Although O2 involvement in the Hb effect was tested by bubbling medium with 100% O2 for 10 minutes, basal and stimulated secretion was unaffected. Since proteins, such as Hb, non-specifically bind free steroids, enhancing secretion, albumin (Al) was compared to Hb. Al enhanced unstimulated, but not ACTH-stimulated, 20-DHP secretion. The Hb effect may not be due to non-specific protein-steroid binding. Ca++ supplementation and chelation studies suggest the necessity to optimize co-factors in steroidogenic tissue incubation media to maximize basal and stimulated steroid synthesis and secretion. Since physiologically relevant Hb levels enhanced basal and stimulated Y-1 cell steroid secretion by mechanisms other than protein-steroid binding and soluble O2 had little effect, Hb may more efficiently transport O2 to cultured cells than soluble O2 diffusion through medium does.