Clinical Evaluation of the Temperature Dependence of Subcutaneous Injection Experience in Healthy Volunteers

To evaluate the clinical effect of the warming step for subcutaneous (SC) injection on injection site pain (ISP).

A single center, randomized, partially blinded, crossover study in 44 healthy participants was conducted. Participants self-injected with autoinjectors (1 mL) with either high pain (citrate/sodium chloride (NaCl)) or low pain (mannitol) formulations at refrigerated temperature or warmed to room temperature (RT) according to the instructions for use (IFU). The ISP was recorded using visual analog scale (VAS) and injection site reactions (ISRs) were captured using severity scores.

The average VAS scores were clinically different between high pain and low pain formulation but not affected by the warming step. While the average VAS was not affected by injectate temperature, some individual participants reported bidirectional VAS responses to injectate temperature. A post injection questionnaire showed that most participants were not bothered by the cold sensation of the injected solution. The clinical results are consistent with modeling that indicates rapid temperature equilibration of subcutaneously injected solutions.

Formulation composition was the dominating factor contributing to ISP as compared to solution temperature due to transient thermal equilibrium of the injected solution in SC tissue. While injection temperature may be a lever for improving the injection experience for some patients, the warming step is unlikely to reduce ISP for most patients. Although this study was conducted with 1 mL injection of two representative formulations, this finding of lack of correlation between ISP and solution temperature is likely extrapolatable to most small volume (e.g., ≤ 2 mL) injections of subcutaneous formulations.