Background Autologous serum can be compounded into eye drops that are used to reduce symptoms of severe dry eye syndrome. In the case of appropriate stability and sterility, frequency of blood drawings from patients might be reduced and clinical logistics simplified.

Purpose To assess the sterility and stability of serum under different storage conditions and prolonged storage time up to 6 months.

Material and methods After obtaining whole blood and preparing unit dose autologous serum eye drops 100% and 50%, samples were stored at 4°C and −20°C for up to 6 months. Concentrations of albumin, immunoglobulin G and C4 (C4c) were used as surrogate stability biomarkers and measured on storage days 1, 8, 15, 30, 60, 90 and 180. Sterility according to European Pharmacopoeia (2.6.1) was evaluated on storage days 1, 15, 30, 60, 90 and 180.

Results The concentrations of albumin and immunoglobulin G remained stable under both temperature conditions over the entire period of 6 months. The C4c concentration increased by about 30% at storage temperature of 4°C. This was not the case for samples stored at −20°C. No difference in C4c concentrations was seen between undiluted and diluted serum. Sterility was maintained in the 4°C and −20°C samples throughout the period tested.

Conclusion The present results show that serum parameters albumin, immunoglobulin G and C4c are stable at −20°C for 6 months. As C4c is a breakdown product of C4b, the increase in C4c at 4°C may be indicative for some instability of C4b. However, this increase is considered mild and values remained within the normal range, and hence this change may have no clinical significance. At both temperatures tested, sterility of serum eye drops was not impacted, including the longest storage duration tested. In summary, the results support using aseptic preparation techniques and storage temperature at −20°C. A 6 month supply of autologous serum eye drops can be offered to patients, allowing better access to this therapy through a less frequent blood donation schedule.

No conflict of interest