Stability of 4 Intravenous Drug Formulations in Prefilled Syringes Stored Frozen for Up to 60 Days

Abstract

Purpose: Prefilled drug syringe use may reduce the cost of routine antibiotic drug delivery. Storage of prefilled syringes frozen (−20°C) or refrigerated (4°C-5°C), can optimize the use of robotic syringe filling systems if acceptable stability data is gathered per USP 797 standards. Methods: Four intravenous (IV) drug formulations were prepared from bulk standard solutions and filled into 10 mL syringes using an Intellifill© IV Robot. Formulations were Piperacillin (2.0 g) and Tazobactam (0.25 g) as 2.25 g in 10 mL; Piperacillin (3.0 g) and Tazobactam (0.375 g) as 3.375 g in 10 mL; Cefuroxime as 1.5 g in 11 mL; and Vancomycin as 1.0 g in 10 mL. Concentrations were assayed at “zero time,” and after 21, 45, and 60 days frozen. Syringes were warmed to room temperature (RT) by gently rolling in hands. Three syringes of each formulation were assayed by stability-indicating HPLC per USP procedures. Assay results are the average of 5 injections of samples from each syringe upon return to RT and repeated for 3 separate syringes maintained at RT for 24 hours. Results: All formulations were stable out to 60 days frozen. Both of the piperacillin/tazobactam formulations were also stable when kept at refrigerated temperature for 9 days. Conclusion: Piperacillin/Tazobactam formulations can be stored frozen (−20°C) for up to 60 days with no appreciable loss. Cefuroxime and Vancomycin formulations can be stored frozen for up to 60 days. Both Piperacillin/Tazobactam formulations can be refrigerated for up to 9 days. Implementation of larger batch compounding coupled with frozen syringe storage and delivery could result in enhanced uniformity of composition and significant manpower savings.

Keywords

stability cefuroxime vancomycin piperacillin-tazobactam prefilled syringes

Introduction

Pre-filled syringes of standard antibiotic drug formulations for intravenous (IV) delivery are commonly used in hospital settings.¹ Prefilled syringes can be made in hospital pharmacy by semi-automated machine systems from commercial bulk drug containers to enhance the cost-effectiveness and uniformity of IV drug delivery.²

However, the cost-effectiveness and uniformity of pre-filled syringe systems are optimal if done in larger batches (possibly once per week) versus an everyday, small batch filling process. Thus, the storage of pre-filled syringes at refrigerated or frozen temperatures is a viable option if appropriate drug stability can be established. Appropriate storage under reduced temperatures can conceivably enhance drug stability and lead to significant manpower savings in hospital IV drug delivery.³ In addition, if short term stability can be established for certain formulations stored at refrigerated temperatures, units of these formulations could be stored on floors or in satellite pharmacies to enhance timely delivery.

The current study evaluated short term IV antibiotic drug stability in 4 prefilled syringe formulations stored frozen for up to 60 days and in 2 formulations stored refrigerated for 9 days.

Materials and Methods

All drug samples were prepared from commercial bulk drug preparations (Pfizer) using sterile water for injection as a uniform diluent. The samples for this study were prepared by the Methodist University Hospital Pharmacy (Memphis, TN) per usual hospital pharmacy procedures in syringes (Intellifill IV) and were delivered to the Center for Pediatric Experimental Therapeutics Laboratory, University of Tennessee Health Science Center (Memphis, TN) immediately after compounding. These 4 formulations are routine hospital IV drug formulations and are commonly used in large tertiary care hospitals.

Formulations were prepared at 1 week intervals to allow adequate analytical time before starting the next round of assays. Each formulation (3 syringes) was evaluated for drug concentrations at “zero time,” immediately upon receipt of the syringes in the lab on the day of filling, and after 21, 45, and 60 days of storage under usual frozen conditions (minus 20°C ± 2.0°C in continuous dark). In addition, both Piperacillin and Tazobactam combination formulations (2 concentrations) were also evaluated after 9 days of storage under usual refrigerated conditions (4°C-5°C in continuous dark). At each analysis time point, each formulation (3 separate syringes) was also evaluated after 24 hours of being maintained at room temperature (RT; 22°C ± 2.0°C) and normal laboratory illumination (roughly 10 hours light, 14 hours dark). Acceptable stability was based on equal to or greater than 90% of “zero time” drug concentration after 24 hours at RT for each time point evaluation (frozen and refrigerated).

All assays were performed by stability-indicating HPLC assays according to current USP procedures including any published updates.^4-6 Three syringes of each formulation were assayed after complete thawing and inspection at each time point. In addition, 3 separate syringes were assayed after 24 hours at RT. Each syringe unit was thawed by hand with gentle rolling and inversion (no exposure to microwave or elevated temperatures). Each unit was inspected for leakage and was inverted slowly for complete mixing of the contents and to ensure that all drug was completely re-solubilized. Visual inspections were done against both light and dark backgrounds. A sample from each syringe was then appropriately diluted for assay with mobile phase per the specific USP procedure. Separate vials of diluted sample from each syringe were placed in the refrigerated auto-sampler (4°C-5°C). Five injections of appropriate volume were made per each USP procedure on the HPLC from each vial. Drug standards and any required internal standard as well as resolution standards were prepared per the USP procedure on each day of assay. The means of 5 injections of standards and samples were used in calculating sample drug concentration for each unit at each time point.

All drug standards, internal standards, resolution standards and HPLC materials were Analytical Grade or better as specified in the USP. All mobile phase solvents and components were HPLC grade. Assays were performed on a Prominence HPLC Instrument with a SPD-M20A Photodiode Array Detector and a Refrigerated Autosampler (Schimadzu Scientific Instruments, USA). Vancomycin was assayed on an L-1 column (Zorbax Eclipse XDB-C-18 Analytical Column, 4.6 × 250 mm, 5-micron from Agilent Technologies, USA) using gradient elution according to the USP for Vancomycin Injection including the Official Errata published May 1, 2011. Cefuroxime was assayed on an L-15 column (PhenoSphere 5 u C6 80A Analytical Column, 4.60 × 150 mm from Phenomenex Corp., USA) using isocratic elution according to the USP for Cefuroxime Injection. Piperacillin and Tazobactam were assayed on an L-11 column (Gemini 3u C6-Phenyl 110A Analytical Column, 4.60 × 150 mm from Phenomenex Corp., USA) using isocratic elution according to the USP for Piperacillin and Tazobactam for Injection, Official Revision Bulletin, February 1, 2010.

The composition of the 4 drug formulations in this study were:

Vancomycin as 1.0 g in 10 mL;

Cefuroxime as 1.5 g in 11 mL;

Piperacillin (2.0 g) and Tazobactam (0.25 g) as 2.25 g in 10 mL; and

Piperacillin (3.0 g) and Tazobactam (0.375 g) as 3.375 g in 10 mL.

Testing for drug concentrations was performed at each of the following intervals: “zero time,” and after 21 days, 45 days, and 60 days frozen. In addition, for the Piperacillin/Tazobactam formulations, syringe units were also evaluated after storage for 9 days at usual refrigerated temperatures.

The results are summarized as the mean ± SD of the 3 units for each formulation at each study time point (total of 15 values) and were compared as percent of both label (ie, theoretical) and “zero time” concentrations for each drug (see Tables 1 –3). Acceptable stability is defined as greater than 90% of “zero time” concentration.

Table 1.

Summary of Vancomycin and Cefuroxime Concentrations for Injection.

	Formulation label	Zero time		21 days frozen		45 days frozen		60 days frozen
	Formulation label	T₀	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT
Vancomycin for injection, Mean ± SD g/10 mL	1.00	1.07 ± 0.0261	1.01 ± 0.0178	1.06 ± 0.0234	1.07 ± 0.0153	1.04 ± 0.00905	1.04 ± 0.00934	1.04 ± 0.00730	1.04 ± 0.0134
% of Label	—	107	101	106	107	104	104	104	104
% of Zero time	—	100	94.4	99.1	100	97.2	97.2	97.2	97.2
Cefuroxime for injection, Mean ± SD g/11 mL	1.50	1.49 ± 0.00318	1.41 ± 0.0546	1.42 ± 0.0273	1.42 ± 0.0164	1.45 ± 0.0471	1.38 ± 0.0204	1.44 ± 0.0122	1.38 ± 0.0243
% of Label	—	99.3	94.0	94.7	94.7	96.7	92.0	96.0	92.0
% of Zero time	—	100	94.6	95.3	95.3	97.3	92.6	96.6	92.6

Note. RT = room temperature 20 ± 2.0°C; Frozen = −20°C.

Table 2.

Summary of High Dose Piperacillin/Tazobactam Concentrations for Injection.

	Formulation label	Zero time		9 days refrigerated		21 days frozen		45 days frozen		60 days frozen
	Formulation label	T₀	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT
Piperacillin for injection, Mean ± SD g/10 mL	3.00	2.97 ± 0.0632	3.03 ± 0.0591	3.07 ± 0.0943	3.23 ± 0.0808	3.06 ± 0.109	3.04 ± 0.0539	3.01 ± 0.0775	2.94 ± 0.0750	3.05 ± 0.0524	3.14 ± 0.109
% of Label	—	99.0	101	102	107	102	101	100	97.9	102	105
% of Zero time	—	100	102	103	108	103	102	101	99.0	103	106
Tazobactam for injection, Mean ± SD g/10 mL	0.375	0.356 ± 0.00563	0.371 ± 0.00668	0.392 ± 0.00995	0.372 ± 0.00787	0.377 ± 0.0124	0.372 ± 0.00665	0.375 ± 0.00951	0.349 ± 0.00815	0.358 ± 0.00448	0.366 ± 0.0128
% of Label	—	94.9	98.9	104	99.2	100	99.2	100	93.1	95.5	97.6
% of Zero time	—	100	104	110	104	106	104	105	98.0	101	103

Note. RT = room temperature 20 ± 2.0°C; Refrigerated = 4°C-5°C; Frozen = −20°C.

Table 3.

Summary of Low Dose Piperacillin/Tazobactam Concentrations for Injection.

	Formulation label	Zero time		9 days refrigerated		21 days frozen		45 days frozen		60 days frozen
	Formulation label	T₀	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT	Thawed	Plus 24 h at RT
Piperacillin for injection, Mean ± SD g/10 mL	2.00	1.96 ± 0.0230	1.96 ± 0.00880	1.92 ± 0.0342	1.98 ± 0.0472	1.95 ± 0.0254	1.96 ± 0.00880	1.94 ± 0.0268	1.84 ± 0.0143	1.93 ± 0.0787	1.94 ± 0.0320
% of Label	—	98.0	98.0	96.0	99.0	97.5	98.0	97.0	92.0	96.5	97.0
% of Zero time	—	100	100	98.0	101	99.5	100	99.0	93.9	98.5	99.0
Tazobactam for injection, Mean ± SD g/10 mL	0.25	0.233 ± 0.00267	0.235 ± 0.00103	0.239 ± 0.00576	0.249 ± 0.00687	0.243 ± 0.00273	0.235 ± 0.00369	0.240 ± 0.00389	0.219 ± 0.00116	0.218 ± 0.00935	0.219 ± 0.00299
% of Label	—	93.2	94.0	95.6	99.6	97.4	94.0	96.0	87.6	87.2	87.6
% of Zero time	—	100	101	103	107	104	101	103	94.0	93.6	94.4

Note. RT = room temperature 20 ± 2.0°C; refrigerated = 4°C-5°C; Frozen = −20°C.

Results

Table 1 summarizes the results for Vancomycin and Cefuroxime. Vancomycin at 1.0 g in 10 mL was found to be stable in frozen prefilled syringes for 60 days. The results at 60 days indicate that the Vancomycin concentration is 1.04 g per 10 mL (label value is 1.0 g/10 mL). Approximately 97.2% of vancomycin (versus “zero time”) remains at the 60 day time point. Note that all vancomycin concentrations are above the label value of 1.0 g/10 mL at all assay time points. This is most likely due to over formulation by the supplier of the bulk vial to assure adequate stability.

Similar results are observed from the assays conducted after separate syringes remained at room temperature for a full 24 hours. Approximately 97% of the initial vancomycin assay value remains. The range across all assay time points was 94.2% to 100% of the initial assay value for syringes kept at RT for 24 hours. The percent coefficient of variation (% CV) for all vancomycin assays ranged from 0.699 (day 60) to 2.45 (day 0).

The value for Cefuroxime at 60 days frozen was 1.44 g per 11 mL (label value of 1.5 g/11 mL). Thus, approximately 96% of Cefuroxime remains at 60 days. At the 60 day frozen plus 24 hours at RT time point, the assay results were 1.38 g/11 mL or 92% of initial value. The corresponding numbers at 45 days plus 24 hours were essentially the same. The % CV for all cefuroxime assays ranged from 0.848 (day 60) to 2.13 (day 0).

Tables 2 and 3 show the results for the 2 different concentrations for the combination of Piperacillin and Tazobactam. For the high concentration (3.0 g Piperacillin and 0.375 g Tazobactam in 10 mL), the average values at 60 days frozen were 3.05 g Piperacillin and 0.358 g Tazobactam per 10 mL. These results are 103% and 101% of the initial (“zero time”) values respectively. After 60 days frozen plus 24 hours at RT, the results were 106% for Piperacillin and 103% for Tazobactam compared to “zero time” values.

The high concentration Piperacillin-Tazobactam was also tested after being stored at refrigerated temperature for 9 days. The average values were 3.07 g Piperacillin and 0.392 g Tazobactam per 10 mL. These values are 103% and 110% respectively relative to the “zero time” values. The results after 24 hours of RT were 108% and 104%, respectively. For all assays of the high Piperacillin-Tazobactam formulation the % CVs ranged from 1.77 (day 21 + 24 hours RT) to 3.46 (day 60 + 24 hours RT) for Piperacillin and 1.58 (day 0) to 3.29 (day 21) for Tazobactam.

For the lower concentration of Piperacillin/Tazobactam (2.0 g Piperacillin and 0.25 g Tazobactam in 10 mL), the results are slightly different. Figures 1 and 2 illustrate the concentrations of piperacillin and tazobactam respectively as a function of time under the different storage conditions. At 45 days frozen, the assay results are 1.94 g Piperacillin and 0.240 g Tazobactam per 10 mL. These results are approximately 99.0% (Piperacillin) and 103% (Tazobactam) of the “zero time” values. However, after syringes remain at RT for 24 hours, the assay results fall to 94.0% of the “zero time” values for both.

At 60 days frozen, the assay results are very similar at 1.93 g Piperacillin and 0.218 g Tazobactam per 10 mL. These values are approximately 98.5% (Piperacillin) and 93.6% (Tazobactam) of the “zero time” values. The assay results for the samples remaining at RT for 24 hours are also similar (99.0% for Piperacillin and 94.0% for Tazobactam) compared to “zero time” values. When refrigerated for 9 days, the average values were 1.92 g Piperacillin and 0.239 g Tazobactam per 10 mL. These results are 98.0% and 103%, respectively of the “zero time” values. The results after 24 hours of RT were 101% and 107%, respectively. For all assays of the lower Piperacillin/Tazobactam formulation the % CVs ranged from 0.449 (day 21 + 24 hours RT) to 4.08 (day 60) for Piperacillin and from 0.438 (day 0 + 24 hours) to 4.23 (day 60) for Tazobactam.

Discussion

Studies of the stability of drugs in the frozen state have been published for at least 4 decades.^7,8 Similarly, the stability of drug formulations in prefilled, ready to deliver syringes has been reported for at least 3 decades.^9,10 Few studies have reported on the stability of drugs (including antibiotics) in syringes when stored at refrigerated and/or frozen temperatures.^11-16 Our novel study extends this literature by combining the evaluation of stability of 4 standard antibiotic formulations in robotically filled syringes stored frozen for up to 60 days. The study also reports the stability of high and low concentrations of piperacillin/tazobactam formulation in syringes refrigerated for 9 days. In addition, our study evaluated the stability of all these formulations in syringes after an additional 24 hours at room temperature. Vancomycin retained potency above 100% of “zero time” values for all time points analyzed, thus showing prefilled syringes stored frozen appear to be stable for at least 60 days. These results are comparable to stability data shown by Mehta et al of frozen syringes with more diluted vancomycin (10 mg/mL) targeted for endophthalmitis treatment.¹⁷ They reported retention of at least 70% of baseline concentration of samples stored at 3 different temperatures for 1, 2, 4, 12, and 24 weeks. Though not statistically significant, samples stored at 4°C had slightly lower concentrations than at the other 2 storage conditions (−20°C and −80°C), while retaining potency and bactericidal effect.¹⁷ Our study shows better retention comparing roughly to the same time frame. Cefuroxime appears almost equally stable as concentrations were approximately 96.6% compared to the “zero time” value at the 60-day time point. This is comparable to data by Feutry et al where cefuroxime (10 mg/mL) frozen syringes showed 96% potency at 56 days.¹⁸ Cefuroxime also appears to be only slightly less stable at RT for 24 hours (92.6% of “zero time” after 60 days frozen plus 24 hours RT).

Our study also analyzed 2 different commercially-available combination doses of Piperacillin-Tazobactam at the same frozen storage time points plus an evaluation of syringes stored for 9 days at refrigerated temperatures. As shown in Table 2, the high concentration Piperacillin-Tazobactam was stable out to 60 days frozen (103% and 101% of “zero time” value respectively). This formulation was also quite stable after 24 hours. RT (106% and 103% of “zero time” respectively). The lower concentration of Piperacillin-Tazobactam results at 60 days frozen are only slightly lower (98.5% and 93.6%, respectively). The corresponding values after 24 hours RT were 99.0% and 94.0%, respectively. Our results indicate both formulations of Piperacillin-Tazobactam (2.0 g-0.25 g/3.0 g-0.375 g) are very stable in syringes stored at refrigerated temperatures for 9 days (approximately 98.0% to 107% of “zero time” values).

Our sole concern with these results is with the low dose tazobactam result at 60 days. Although the comparison to “zero time” values is the appropriate comparison for stability studies, the approximately 87% result when comparing to the “theoretical” or label value is a minor concern. However, since the “zero time” value for this concentration was approximately 93% to 94% of label, this concern is indeed minor. Stability results such as these are encouraging and can provide tangible evidence to assist health-system pharmacy better manage their inventory, especially in times of drug shortages. Prefilled drug syringe use may reduce the cost of routine antibiotic drug delivery, which can be advantageous to both large and small healthcare facilities.

Conclusion

The data from this study support the conclusion that prefilled syringes of these 4 drug formulations can be maintained in the frozen state for up to 45 days, quickly thawed and administered, without compromising drug potency. Similarly, our results support the routine storage of prefilled syringes of both Piperacillin-Tazobactam concentrations refrigerated for up to 9 days. The use of robotic syringe filling systems may reduce manpower costs by allowing for larger batch production.

Footnotes

Acknowledgements

The authors gratefully acknowledge the assistance of Caitlin Gewin, BS with syringe storage, analytical sample preparation, and data entry. The authors received financial support from the Center for Pediatric Experimental Therapeutics (CPET) and from Methodist University Hospital, Memphis, TN.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Oscar R. Herrera

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