Extended Stability of Vasopressin Injection in Polyvinyl Chloride Bags and Polypropylene Syringes and Its Impact on Critically Ill Patient Care and Medication Waste

Abstract

Background. Vasopressin is frequently utilized for a variety of shock states in critically ill patients. Short stability (≤24 hours) after intravenous admixture with current manufacturer labeling requires just in time preparation and may lead to delays in therapy and increased medication waste. We aimed to evaluate vasopressin stability in 0.9% sodium chloride stored in polyvinyl chloride bags and polypropylene syringes for up to 90 days. Additionally, we evaluated the impact of extended stability on the time to administration and cost savings from reduced medical waste at an academic medical center. Methods. Dilutions of vasopressin to concentrations of 0.4 and 1.0 unit/mL were performed under aseptic conditions. The bags and syringes were stored at room temperature (23°C-25°C) or under refrigeration (3°C-5°C). Three samples of each preparation and storage environment were analyzed on days 0, 2, 14, 30, 45, 60, and 90. Physical stability was performed by visual examination. The pH was assessed at each point and upon final degradation evaluation. Sterility of the samples was not assessed. Chemical stability of vasopressin was evaluated using liquid chromatography with tandem mass spectrometry. Samples were considered stable if there was <10% degradation of the initial concentration. Results. Vasopressin diluted to 0.4 and 1.0 unit/mL with 0.9% sodium chloride injection was physically stable throughout the study. No precipitation was observed. At days 2, 14, 30, 45, 60, and 90 all bags and syringes diluted to 0.4 units/mL had <10% degradation. Vasopressin diluted to 1 unit/mL and stored under refrigeration had <10% degradation at all measured days, but when stored under room temperature was found to have >10% degradation at day 30. Implementation of a batching process resulted in reduced waste ($185 300) and improved time to administration (26 vs 4 minutes). Conclusion. Vasopressin diluted to a concentration of 0.4 units/mL with 0.9% sodium chloride injection is stable for 90 days at room temperature and under refrigeration. When diluted to 1.0 unit/mL with 0.9% sodium chloride injection it is stable for 90 days under refrigeration. Use of extended stability and sterility testing to batch prepare infusions may lead to improved time to administration and cost savings from reduced medication waste.

Introduction

Vasopressin, synthetic arginine vasopressin, is a peptide which replicates the actions of the naturally occurring hormone of arginine vasopressin released from the posterior pituitary. ¹ Its vasopressin 1 (V₁) and vasopressin 2 (V₂) agonist properties produce vasoconstriction within smooth muscle and an antidiuretic effect. ² Due to these effects, vasopressin is commonly used for circulatory support during vasodilatory shock, diabetes insipidus, and bleeding esophageal varices.^{3 -5} Vasopressin is also widely used in septic shock and reduces exogenous vasopressor requirements.^{6 -8} Concentrated vasopressin, typically 20 units/mL concentration, must be further diluted for when the medication is to be administered as a continuous intravenous infusion. Vasopressin for intravenous infusion is commonly diluted with normal saline or 5% dextrose in water to concentrations ranging from 0.1 to 1.0 unit/mL. ¹

Arginine vasopressin’s chemical name is Cyclo (1-6) L-Cysteinyl-L-Tyrosyl-L-Phenylalanyl-L-Glutaminyl-L-Asparaginyl-L-Cysteinyl-L-Prolyl-L-Arginyl-L-Glycinamide with a molecular weight of 1084.23 amu. Biological potency of arginine vasopressin varies between batches with 1 mg approximately equivalent to 530 units. Neutral salts can affect the stability of macromolecules, such as arginine vasopressin, in solution. One common cause of insolubility for peptides in solution is alteration in quaternary structure secondary to interactions with nonpolar side chains which can lead to aggregation. The current recommendation is for arginine vasopressin to be diluted in 0.9% sodium chloride solution at a concentration of 0.1 units/mL within polyvinyl chloride bags for up to 18 hours at room temperature or 24 hours under refrigeration. ¹

Intravenous admixtures with less than or equal to 24 hours dating are problematic for health systems due to requirements for just in time preparation and short beyond use dates increase risk of waste.^{9 -14} Therefore, the purpose of this study was to determine the physical and chemical stability of arginine vasopressin at concentrations of 0.4 and 1.0 unit/mL in 0.9% sodium chloride when stored at room temperature or refrigerated for up to 90 days ¹⁵ and the impact of extended stability on patient care and medication waste.

Methods

Sample Preparation

Dilution of vasopressin^a to a nominal concentration of 0.4 and 1.0 unit/mL was performed by the University of Colorado Hospital pharmacy under aseptic conditions in an International Standards Organization class 7 environment by adding vasopressin 20 units (20 units/1.0 mL) to 49 mL of 0.9% sodium chloride for injection in a PVC bag^b and polypropylene syringe^c and 10 units of vasopressin (20 units/1.0 mL) respectively and 9.5 mL of 0.9% sodium chloride for injection in a polypropylene syringe.^d Accurate volumes were achieved by removing all 0.9% sodium chloride for injection from all polyvinyl chloride bags and exact volumes of 0.9% sodium chloride for injection were then injected into the polyvinyl chloride bags utilizing a graduated syringe. For syringe storage studies, accurate volumes were achieved by drawing 1.0 or 0.5 mL into a graduated syringe^c,d and then exact volumes of 0.9% sodium chloride for injection were drawn into the graduated syringes. Three separate preparations were created for each concentration and storage condition on study day 0. The bags and syringes were then refrigerated (3°C-5°C) or stored at room temperature (23°C-25°C) under normal fluorescent lighting. Refrigerated samples were allowed to warm to room temperature before sampling. No external source of heat was used to warm the bags. Three bags and syringes for each of the storage condition were assessed for physical and chemical stability over 90 days. The original concentration of each preparation was evaluated on day 0. Stability was assessed on days 2, 14, 30, 45, 60, and 90. Sterility of the samples was not assessed.

Physical Evaluation

Physical stability of vasopressin was assessed by visual examination. Solutions were evaluated against black and white backgrounds for visible particulate matter, cloudiness, and color change. Identification of smaller particulate matter using the light obscuration particle count test or the microscopic particle count test was not performed. The pH (Orion Star pH meter)^I was assessed on day 0 and at each time of high-performance liquid chromatographic mass spectrometry—mass spectrometry analysis.

High-Performance Liquid Chromatographic Analysis

Vasopressin concentrations were determined by liquid chromatography with tandem mass spectrometry (LC/MS-MS).^e The system was equipped with a HPLC^f and auto-sampler.^g LC/MS-MS methods: Liquid chromatography employed a C₁₈^h column, with column guard, set at 40 ± 1°C with a flow-rate of 0.4 mL/min. The mobile phase consisted of A: 10 mM (NH₄OAc), 0.1% formic acid in H₂O, and B: 1:1 acetonitrile: MeOH. The chromatography method used was 95% A for 0.5 minute; ramped to 95% B at 5.5 minutes, held for 1.5 minute, and then brought back to 95% A at 8.0 minutes and held for 1.0 minute (9 minutes total run time). Three Multiple reaction monitoring (MRM) transitions were monitored, MRM (M + H⁺) 1084.40 → 1084.40 m/z (CE = 12, CXP = 10), MRM (M + 2H⁺) 542.80 → 328.24 (CE = 27, CXP = 10); this MRM is qualifier MRM; and, the MRM (M + 2H⁺) 542.80 → 120.07 (CE = 61, CXP = 6); this MRM is the one used for quantitation. The retention time was 3.7 ± 0.1 minutes (Figure 1).

Figure 1.

(a) A representative chromatogram with a peak for vasopressin. Vasopressin peak (blue line) at 3.6 minutes. (b) A representative MRM chromatogram for vasopressin peaks and for internal standard, haloperidol. Vasopressin and degradation product peaks at 3.6 minutes. IS = internal standard.

Standard curves of vasopressin were prepared and chromatogram area under the curve were used to determine vasopressin concentrations. All samples for each storage condition were assayed in triplicate. Calibration of the LC/MS-MS system was performed by construction of a standard curve using 11 known concentrations of vasopressin and was conducted on each of the 6 study days. Coefficients of determination (r ² ) for the standard curve were 0.95 or greater for the entire study. Our assay met the best practice standards set for bioanalytical method validation. ¹⁶

Degradation studies were performed to demonstrate the stability-indicating nature of the assay using vasopressin solution (PAR Pharmaceuticals, Chestnut Ridge, NY) containing 0.80 units/mL (~33.5 µM). The degradation reactions were conducted in a total volume of 200 µL which included 20 µL of vasopressin solution and 20 µL of either 100 mM HCl, 100 mM NaOH or 100 µM NaOCl. After 60 minutes, HCl and NaOH reactions were neutralized with 20 µL NaOH or HCl respectively; NaOCl was diluted with 20 µL water. Each sample was diluted to 500 µL with 280 µL of acetonitrile:methanol containing internal standard haloperidol (376.180 → 165.140; PD 96, CE of 33.0, and CXP 12 and analyzed by LC/MS-MS; t_R 5.5 minutes (Figure 1b). Reductions in area under the curve for each condition are depicted in Figure 2. Identification of degradation products and assessment of their potential therapeutic or toxic effects was not performed.

Figure 2.

The figure shows the reduction in vasopressin concentration under various forced degradation conditions. Columns represent the area under the peak chromatogram measurements under each forced degradation condition at 60 minutes.

Stability Analysis and Statistics

Vasopressin concentrations were measured and analyzed by linear regression using GraphPad Prism 6.07 for Windows. The percentage of vasopressin remaining at each time point was determined with the 90% confidence interval. Concentrations expressed as percent of the initial concentration value (fixed) were fit to obtain a slope and 90% confidence interval. Samples were considered stable if there was less than 10% degradation of the initial concentration based on the slope of vasopressin concentration over time or based on individual time points for 60 and 90 days. Cost of a prepared vasopressin 40 units/100 ml bag at the time of evaluation was $643.40. Cost savings were determined by a wastage study over a 1 month period prior to implementation of vasopressin batching and multiplied by 12 months to get an annual cost savings. Time to vasopressin administration was determined by time of pharmacist order verification to the administration time scan of the medication bag by the bedside nurse in the electronic medical record (EPIC^®). Time difference was compared with a t-test with Welch correction. P < .05 was considered significant.

Results

Vasopressin diluted to 0.4 and 1.0 unit/mL with 0.9% sodium chloride injection was physically stable throughout the study. Solutions kept under refrigeration or at room temperature remained clear throughout the study. No precipitation was observed. At baseline, the mean ± S.D. pH results were as follows: The 0.4 units/ml bags at room temperature (4.12 ± 0.02) and refrigerated (4.10 ± 0.08), the 0.4 units/ml syringes at room temperature (4.15 ± 0.04) and refrigerated (4.13 ± 0.04), and the 1 units/ml syringes at room temperature (4.07 ± 0.06) and refrigerated (4.05 ± 0.06), respectively. These numbers did not change appreciably throughout the study and were 4.08 ± 0.02, 4.15 ± 0.09, 4.14 ± 0.03, 4.14 ± 0.06, 4.08 ± 0.03, and 4.07 ± 0.04 on day 90, respectively. The pH of all study conditions ranged from a minimum of 3.98 to a maximum of 4.19 throughout the duration of the study.

The vasopressin chemical stability results throughout the study are shown in Tables 1 and 2. The lower limit of the 90% confidence interval remained above 90% potency for all storage conditions except 1 unit/mL at room temperature which became unstable between testing days 14 and 30. The mean ± SD concentration units/mL of the room temperature 0.4 units/mL concentration in 0.9% sodium chloride injection in polypropylene bag at baseline was 0.35 ± 0.006 units/mL and Day 90 0.36 ± 0.02 units/mL. The mean ± SD concentration units/mL of the refrigerated temperature 0.4 units/mL concentration in 0.9% sodium chloride injection in PVC bag at baseline was 0.35 ± 0.006 units/mL and Day 90 was 0.36 ± 0.02 units/mL. The mean ± SD concentration units/mL of the room temperature 0.4 units/mL concentration in 0.9% sodium chloride injection in polypropylene syringe at baseline was 0.35 ± 0.005 units/mL and Day 90 was 0.35 ± 0.009 units/mL. The mean ± SD concentration units/mL of the refrigerated temperature 0.4 units/mL concentration in 0.9% sodium chloride injection in polypropylene syringe at baseline was 0.35 ± 0.011 units/mL and Day 90 0.36 ± 0.010 units/mL. The mean ± SD concentration units/mL of the room temperature 1.0 units/mL concentration in 0.9% sodium chloride injection in polypropylene syringe at baseline was 0.81 ± 0.064 units/mL and Day 90 was 0.78 ± 0.045 units/mL. The mean ± SD concentration units/mL of the refrigerated temperature 1.0 units/mL concentration in 0.9% sodium chloride injection in polypropylene syringe at baseline was 0.78 ± 0.005 units/mL and Day 90 was 0.81 ± 0.032 units/mL. No new degradation peaks were observed, and concentrations of the unidentified peaks did not increase.

Table 1.

Stability of Arginine Vasopressin in 0.9% Sodium Chloride Injection in a PVC Bag.

Vasopressin concentration *	Storage conditions	% initial concentration remaining
		Day 2	Day 14	Day 30	Day 45	Day 60	Day 90
0.4 units/mL PVC bag	Room temperature	105.6 ± 1.2	105.4 ± 5.5	101.3 ± 2.5	101.5 ± 2.2	99.5 ± 0.7	102.2 ± 6.3
	Refrigeration	102.5 ± 2.1	101.4 ± 2.2	100.6 ± 1.8	102.2 ± 1.1	104.5 ± 2.8	103.1 ± 4.9
0.4 units/mL Polypropylene syringe	Room temperature	99.5 ± 5.2	100.1 ± 1.1	100.2 ± 4.8	100.1 ± 2.7	100.4 ± 3.4	100.0 ± 2.7
	Refrigeration	102.2 ± 2.4	101.5 ± 1.2	101.3 ± 4.1	103.9 ± 0.7	101.5 ± 3.2	103.3 ± 2.7

^*See results text for baseline and final concentrations.

Table 2.

Stability of Arginine Vasopressin in 0.9% Sodium Chloride Injection in a Polypropylene Syringe.

Vasopressin concentration *	Storage conditions	% initial concentration remaining
		Day 2	Day 14	Day 30	Day 45	Day 60	Day 90
1 unit/mL Polypropylene syringe	Room temperature	88.3 ± 5.4	99.7 ± 2.6	87.4 ± 3.0	88.4 ± 4.0	97.5 ± 5.2	96.0 ± 5.5
	Refrigeration	103.1 ± 4.8	102.6 ± 3.9	96.3 ± 10.9	98.3 ± 5.2	99.7 ± 5.1	104.3 ± 4.1

^*See results text for baseline and final concentrations.

During the wastage month evaluation, 24 vasopressin bags were discarded resulting in an estimated cost of approximately $185 300 annually if 100% of the expired product could be reduced with extended stability batching and sterility testing. Time from pharmacist order verification to nursing administration scan was reduced from an average of 26 ± 13 to 4 ± 6 minutes (P < .01) after changing the process from central pharmacy preparation to unit pyxis machine stocking of the vasopressin infusions.

Discussion

The manufacturer of arginine vasopressin recommends unopened vials of vasopressin be stored between 2°C-8°C controlled temperature until manufacturers expiration or 12 months unopened at room temperature. ¹ To the authors knowledge no current data is published utilizing a stability-indicating methodology regarding vasopressin stability in 0.9% sodium chloride. The present study showed all refrigerated bags and syringes at both concentrations retained greater than 90% vasopressin concentration out to 90 days. All room temperature preparations at 0.4 units/mL concentration retained greater than 90% vasopressin concentration out to 90 days. While some assay values for vasopressin 1.0 unit/mL in syringes at intermediate time points were below 90% potency, values at 60 and 90 days support the long-term stability of vasopressin 1.0 unit/mL stored in polypropylene syringes at room temperature or under refrigeration. ¹⁵ When evaluating over two years of clinical use of these batched vasopressin preparations (PVC bags and polypropylene syringes at 0.4 units/mL stored at room temperature or under refrigeration and 1.0 unit/mL polypropylene syringes stored under refrigeration) at our institution, we have not observed any problems related to reduced efficacy or increased adverse events that would suggest loss of potency or formation of toxic degradation products. Considering the consistent nature of the stability across conditions, it is likely the lower reported concentrations are the result of sampling, dilution or assay error on those days and stability to 90 days is consistent with current premixed products available on the US market. ¹⁷ Despite this extended stability for 90 days based on product environment, the sterility of the prepared vasopressin solution must be assessed according to the standards in chapter 797 of the United States Pharmacopeia. ¹⁸

Given the increase in vasopressin cost of greater than 1138%, hospital administrators have sought ways to reduce the impact of vasopressin on overall drug expenditures.^19,20 This stability study supports a 90-day room temperature or refrigeration shelf life, given the need for a 14-day sterility assessment for low-risk batched products per USP 797 requirements. Vasopressin preparations can be batched centrally and placed within automated dispensing cabinet at desired locations or stored in satellite pharmacies within the facility. This proximity to the patient allows the clinical team to have rapid access to vasopressin infusions, reducing the amount of time to drug delivery and administration. This reduction in administration time can allow for rapid treatment of patients such as septic shock patients requiring hemodynamic management. ²¹ This may improve provider satisfaction and decrease stress for pharmacy IV room staff and pharmacists. The ability to batch vasopressin will reduce drug waste through reuse of product and allow for room temperature storage. Medication errors due to improper dilution of the drug will be significantly reduced and some cost savings can be realized by using the larger, “bulk 10-mL” vials compared with the smaller 20 unit/1.0 ml vial.

At the University of Colorado Hospital, we implemented batch production of the 0.4 unit/ml bags for ICU use and 1 units/ml syringes for operating room use. During the first year of implementation cost savings were realized through decreased inventory of vials, changes in infusion product sizes and decreased waste. Until usage patterns in each patient care area were adjudicated, expiration dates were monitored and stock moved to areas of higher usage to avoid further waste. Estimated cost savings were approximately $185 300 in year one. Establishing a longer BUD with room temperature storage allowed for improved availability through storage in an Automated Dispensing Cabinet (Pyxis/Omnicell) improving provider and nursing satisfaction and improving time to medication administration from an average of 26 minutes to less than 5 minutes from time of order verification. Given the importance of timeliness of medications in patients with shock, having guideline based vasopressor agents on the critical care unit may lead to improved patient outcomes and reduce adverse events from more chemically stable medications readily available in premixed bags (eg, dopamine).^21,22

Conclusion

Vasopressin diluted to a concentration of 0.4 units/mL with 0.9% sodium chloride injection was stable for 90 days at room temperature and under refrigeration. When diluted to 1.0 unit/mL with 0.9% sodium chloride injection, vasopressin was stable for 90 days under refrigeration. Extended stability may result in reduced cost and shortened time to medication availability and administration.

Appendix of Medications, Supplies, and Equipment Used Within the Study Methods

• ^aVasopressin for injection, 20 units/mL, 1.0 mL vial, Par Pharmaceutical Co., Chestnut Ridge, NY, lot 303025

• ^b0.9% sodium chloride for injection, 50 mL in polyvinyl chloride bag, Baxter Healthcare Corporation, Deerfield, IL, lot P366807

• ^c60 mL polypropylene syringe, Becton, Dickinson and Company, Franklin Lakes, NJ

• ^d10 mL polypropylene syringe, Becton, Dickinson and Company, Franklin Lakes, NJ

• ^eSciex 4000 LC-MS/MS, Applied Biosystems, Waltham, MA

• ^fShimadzu HPLC, Shimadzu Scientific Instruments, Columbia, MD

• ^gPAL auto-sampler, LEAP Technologies, Carrboro, NC

• ^hZorbax extended-C18 50 x 4.6 mm, with column guard, Agilent Technologies, Santa Clara, CA

• ^IThermo Scientific Orion 2-Star pH meter. Thermo Scientific. Beverly, MA