What is the stability and sterility data for regular insulin stored in polypropylene syringes under refrigeration?

What is the stability and sterility data for regular insulin stored in polypropylene syringes under refrigeration?

Comment by InpharmD Researcher

Overall, stability data for regular insulin stored in syringes is sparse. Two studies have observed stability in polypropylene syringes for up to 28 days (Tables 1 and 2). Additional studies investigate stability of insulin mixed with 0.9% NaCl solution in polyvinyl chloride and polypropylene bags, demonstrating stability for 24 hours to 14 days.

human insulin polypropylene

Background

A 2022 study investigated the physicochemical stability of ready-to-administer human insulin 1 IU/mL injection solution from two different brands (Huminsulin® and Actrapid Penfill®) when stored in disposable 50 mL plastic syringes. The products were diluted with 0.9% NaCl, prepared in polypropylene syringes (PVC and latex-free), and stored for 90 days at 2-8°C dark room or 20-25°C diffused light room. The results found that the concentration was stable (> 90%) after 90 days in the 2-8°C group, but was stable for at least 14 days in the 20-25°C group. [1]

Relevant Prescribing Information

Unopened HUMULIN R vials may be stored for up to 31 days at room temperature or until expiration under refrigeration. Opened HUMULIN R vials may be stored for 31 days at both room temperature and under refrigeration.

Diluted HUMULIN R for subcutaneous injection may be stored for 28 days when refrigerated at 36° to 46°F [2° to 8°C] or for 14 days at room temperature up to 86°F (30°C).

Intravenous infusion bags prepared with HUMULIN R may be stored for 48 hours when refrigerated at 36° to 46°F [2° to 8°C]. The prepared intravenous infusion bags may then be stored at room temperature for up to an additional 48 hours.

Literature Review

A search of the published medical literature revealed 4 studies investigating the researchable question:

What is the stability and sterility data for regular insulin stored in polypropylene syringes under refrigeration?

Level of evidence

C - Multiple studies with limitations or conflicting results Read more→

Please see Tables 1-4 for your response.

Stability of U-500 regular insulin in prefilled syringes
Design	Stability study
Objective	To determine if U-500 insulin is stable when stored in prefilled syringes at 4°C for up to 28 days
Methods	Insulin U-500 (Humulin R) was drawn up into 1 mL polypropylene syringes in a clean, nonsterile environment to emulate the conditions of a patient’s home. In each syringe, 0.25 mL (125 U) were drawn up; a total of 15 samples were created. The samples were stored under refrigeration (3-5°C). At time point 0 (baseline) and after 7, 14, 21, and 28, three of the stored syringes were removed for high-performance liquid chromatography (HPLC) analysis.
Duration	Up to 28 days
Results		Percent of initial concentration remaining
	Day 7	97.848 ± 0.629%
	Day 14	99.432 ± 3.857%
	Day 21	99.906 ± 2.389%
	Day 28	93.317 ± 2.379%
	The drop in percentage remaining (7%) was not considered statistically significant.
Study Author Conclusions	U-500 insulin in prefilled syringes stored at 4°C is stable for up to 28 days. Prefilled syringes containing U-500 insulin and stored at 4°C for up to 28 days can be used confidently by caregivers for treating patients with diabetes with severe insulin resistance who are unable to independently manage a traditional vial and syringe.
InpharmD Researcher Critique	While the methodology of this study was sound, the individual values were not reported. The prescribing information for U-500 insulin states that it must be used within 31 days of initial use or otherwise should be discarded. This should be taken into consideration when preparing prefilled syringes of U-500 insulin for subsequent storage.

References:
[1] Lull ME, Piacentino JJ, Traina AN. Stability of U-500 regular insulin in prefilled syringes. J Am Pharm Assoc (2003). 2013;53(3):304-306. doi:10.1331/JAPhA.2013.12164

Stability and sterility of biosynthetic human insulin stored in plastic insulin syringes for 28 days
Design	Stability study
Objective	To determine the stability of a variety of biosynthetic human insulin products along with their preservatives when stored in two commonly used plastic insulin syringes
Methods	Samples of regular, isophane, combination, and extemporaneously prepared combination were prepared. Aliquots of 0.4 mL were withdrawn from multidose vials and were stored in 1 mL polypropylene syringes. Three syringes of each type were analyzed initially, with additional samples stored in plastic bags at room temperature (23 °C) and under refrigeration (4 °C). Samples were assessed for potency using high-performance liquid chromatography (HPLC) at days 1, 3, 7, 14, 21, and 28 days; sterility was tested after 1, 2, and 4 weeks.
Duration	Test period: 28 days
Outcome Measures	Potency over 28 days
Results	Endpoint	Day 0	Day 1	Day 3	Day 7	Day 14	Day 21	Day 28
	% Initial concentration remaining 4 °C 23 °C	100.0 ± 0.8 100.0 ± 0.8	102.3 ± 4.0 99.8 ± 0.4	104.6 ± 4.3 102.1 ± 3.8	101.0 ± 2.0 100.0 ± 2.9	99.2 ± 0.8 100.2 ± 3.0	101.9 ± 1.2 100.0 ± 0.4	100.6 ± 1.1 98.1 ± 5.2
	Recovery of m-cresol 4 °C 23 °C	101.0 ± 4.2 101.0 ± 4.2	100.4 ± 4.2 97.3 ± 1.4	101.0 ± 3.5 96.5 ± 1.6	95.2 ± 2.1 85.3 ± 2.1	94.9 ± 2.3 88.1 ± 5.8	94.8 ± 1.5 78.3 ± 2.1	94.7 ± 0.6 76.1 ± 3.1
	Recovery of phenol 4 °C 23 °C	102.0 ± 1.0 102.0 ± 1.0	101.6 ± 1.0 100.1 ± 1.5	102.6 ± 1.9 98.5 ± 0.5	104.1 ± 5.0 102.4 ± 4.4	95.0 ± 0.3 90.6 ± 1.2	98.3 ± 5.9 88.1 ± 1.9	100.2 ± 8.3 92.9 ± 1.4
	Results above have been filtered to focus on regular insulin stored in polypropylene.
Study Author Conclusions	The human insulin products studied remained stable and sterile during 28 days of storage at room and refrigerator temperatures in two types of plastic syringes. Because concentrations of the preservatives decreased more during storage at room temperature, prefilled syringes should be stored in the refrigerator.
InpharmD Researcher Critique	This study was dated, having been conducted in 1991. Modern day insulin formulations and manufacturing standards and procedures may impact stability. Data collection for this study was limited to 28 days.

References:
[1] Tarr BD, Campbell RK, Workman TM. Stability and sterility of biosynthetic human insulin stored in plastic insulin syringes for 28 days. Am J Hosp Pharm. 1991;48(12):2631-2634.

Evaluation of the maximum beyond-use-date stability of regular human insulin extemporaneously prepared in 0.9% sodium chloride in a polyvinyl chloride bag
Design	Stability study
Objective	To evaluate the extended stability of such extemporaneously prepared regular human insulin, stored under refrigeration, to the maximum beyond-use-date allowed by United States Pharmacopeia chapter <797>
Methods	One milliliter of regular human insulin was withdrawn from an unopened vial and added to a polyvinyl chloride bag of normal saline to yield a total of 100 mL. A total of 8 mL of overfill was removed from each PVC bag prior to adding insulin to account for the additional volume (7 mL of overfill plus 1 mL of insulin). This process was repeated in triplicate. Each bag was stored under refrigeration at 2°C–8°C. All samples underwent high-performance liquid chromatography testing at 12 time points over the course of two weeks.
Duration	Up to 336 hours (14 days)
Results	Insulin in NS (U/mL)	Bag 1	Bag 2	Bag 3	Considered stable?
	0 hours	0.92±0.04	0.91±0.01	0.92±0.02	Yes
	6 hours	0.88±0.01	0.89±0.04	0.89±0.02	Yes
	24 hours	0.83±0.03	0.86±0.04	0.85±0.03	Yes
	48 hours	0.84±0.01	0.82±0.03	0.84±0.03	Yes
	72 hours	0.78±0.03	0.83±0.01	0.82±0.05	Yes
	144 hours	0.85±0.02	0.84±0.03	0.87±0.04	Yes
	168 hours	0.79±0.01	0.82±0.03	0.79±0.03	No
	192 hours	0.87±0.00	0.86±0.03	0.88±0.03	Yes
	216 hours	0.82±0.04	0.89±0.01	0.89±0.06	Yes
	240 hours	0.81±0.03	0.86±0.05	0.84±0.01	Yes
	312 hours	0.82±0.06	0.90±0.00	0.88±0.05	Yes
	336 hours	0.91±0.01	0.92±0.02	0.91±0.02	Yes
	At 6 hours, the equilibrium concentration was determined to be 0.89 units/mL. The bags were considered stable if the mean concentration of the samples exceeded 90% of the equilibrium concentration at 6 hours.
Study Author Conclusions	Based on these results, regular human insulin 100 units added to 0.9% sodium chloride for injection in a PVC bag to yield a total volume of 100 mL is stable for up to 336 hours when stored at 2°C–8°C (36°F–46°F).
InpharmD Researcher Critique	This study extemporaneously prepared regular human insulin 100 units to normal saline IV bags starting with unopened vials. Notably, at 168 hours, two of the samples were not considered stable (lost >10% potency); however, the future evaluations returned back to acceptable concentrations. There is no proposed explanation for this change in concentration.

References:
[1] Rocchio MA, Belisle CD, Greenwood BC, Cotugno MC, Szumita PM. Evaluation of the maximum beyond-use-date stability of regular human insulin extemporaneously prepared in 0.9% sodium chloride in a polyvinyl chloride bag. Diabetes Metab Syndr Obes. 2013;6:389-392. Published 2013 Oct 11. doi:10.2147/DMSO.S51843

Evaluation of regular insulin adsorption to polypropylene bag and polyvinyl chloride infusion set
Design	Stability analysis of pharmacologic products
Objective	To evaluate the rate of adsorption of regular insulin to polypropylene (PP) bags and polyvinyl chloride (PVC) infusion sets and stability of insulin during the infusion
Methods	Regular insulin (Humilin R, Lily®) and PP bags (Polifarma®) were utilized to make six insulin bags for the analysis. The insulin was prepared by adding 100 IU of regular insulin to 100 mL of 0.9% NaCl solution (unspecified manufacturer) to make a concentration of 1 IU/mL. Based on a mock infusion rate of 2 IU/hour, 600 uL (microliters) samples were drawn at hours 0, 1, 2, 4, 12, and 24 hours to be analyzed for stability and rate of adsorption to bag. Samples were also stored at +25°C (room temperature) and +4°C (refrigerated) with samples drawn at hours 0, 4, 12, and 14. Regular insulin concentrations in PVC infusion sets were observed but were not included in this table. The stability of insulin in PVC infusions at room and refrigerated temperatures was not analyzed and could not assist in determining how PVC may affect the BUD.
Duration	24 hours
Outcome Measures	Concentration of samples at various time points.
Results		Insulin samples (N=6)
	Mean percentage of insulin concentrations detected Hour 0 Hour 1 Hour 2 Hour 4 Hour 12 Hour 24	100% ± 0 95 ± 4.203 98 ± 1.049 98 ± 2.270 95 ± 3.606 100 ± 3.311
	Mean percentage of insulin concentrations detected at 4°C Hour 0 Hour 4 Hour 12 Hour 24	100% ± 0 102% ± 1 100% ± 0 100% ± 0
	Mean percentage of insulin concentrations detected at 25°C Hour 0 Hour 4 Hour 12 Hour 24	100% ± 0 100% ± 0 98% ± 1 102% ± 1
	No statistical difference between concentrations of samples taken from PP bags stored at hours 4, 12, and 24 (p>0.05).
Study Author Conclusions	When PP bags are used for insulin infusion, it is predicted that 24-hour change can be made instead of frequent change. In addition, losses caused by the high rate of insulin adsorption to PVC infusion sets should be considered and PP infusion sets would be the better option to use if available.
InpharmD Researcher Critique	Though the regular insulin and the NS fluids were from different manufacturers, B. Braun Medical Inc NS plastic bags are made from polypropylene mixed with thermoplastic modifier. This study is similar to the conditions of the inquiry by observing the stability of regular insulin in NS fluid stored in a polypropylene bag (though whether the bag is also made from thermoplastic modifier or not is unknown). Unfortunately, the authors did not observe the stability of regular insulin and PVC at different temperatures.

References:
[1] Sürmelioğlu N, Nenni M, Fırat A, Demirkan K, Özcengiz D. Evaluation of regular insulin adsorption to polypropylene bag and polyvinyl chloride infusion set. Int J Clin Pract. 2021;75(4):e13895. doi:10.1111/ijcp.13895