Overview
The delivery of parenteral therapeutics through an intravenous (IV) route often involves contact with different materials associated with IV-administration devices. "In-use" stability studies are designed to ensure no loss of product quality during storage and administration. However, excipients, which are used to stabilize the drug product formulation, may also facilitate the solubilization of leachables from material contact. Typically, monitoring leachables from the administration devices is limited, especially during the early stages of product development. In this article, we provide an overview of in-use stability studies and the effect of common formulation excipients on leachables levels during product in-use storage and administration.
Introduction
During the formulation development process, excipients are selected to maintain product quality and stability. In some cases, excipients are used to improve the solubility of the active, while in other cases excipients may be needed to provide protection against physical stresses like agitation or freeze/thaw temperature cycling [1, 2]. However, the same properties of the excipients that facilitate an increase in the solubility of the active and the physical stability of the product may also facilitate leaching of compounds upon contact with various plastic materials [3].
For parenteral products intended for IV administration, generally the main material contact is with the primary packaging consisting of the glass vial and stopper. However, in some cases, product administration may require the preparation of an admixture solution and the use of an IV-bag, IV-line, and catheter. During this type of administration, an admixture solution is exposed to different plastic fluid-path materials. For example, the IV-bag and IV-line may be constructed of polyvinylchloride material, while the in-line filter may be constructed of polyethersulfone. If leachables during administration are a concern, then to evaluate leachables, an appropriate admixture "in-use" study design as well as an accurate assay to quantify the leachables is needed. Based on these results an appropriate control strategy can be developed.
The evaluation of leachables earlier in the product development process, such as during formulation screening, may ultimately provide additional flexibility for product administration prior to the selection of the clinical and commercial formulation. Specifically, the choice of excipients to minimize leachables may provide more flexible administration options in the clinic.
In this article, we provide an example of how leachables may be controlled by changes to the formulation excipients. In addition, we summarize some key design highlights to admixture "in-use" studies in the context of potential leachables.
In-use Stability Studies
The goal of the admixture in-use admixture stability study is to ensure that the product quality does not change upon initial product dilution and subsequently through storage through administration. In-use stability studies typically evaluate compatibility of the admixture with the diluent (e.g., normal saline or 5% dextrose solution) and fluid-path contact material. The in-use study should be designed to evaluate the concentration ranges that provide the desired dose levels in the clinic. Generally, bracketing the lowest and highest dose levels and corresponding admixture concentrations can be used to efficiently design the experiment. Other considerations in the study design include: the clinical dosing strategy, the administration material availability, and hold times and storage conditions [4]. Prior to initiating these studies, it is helpful to determine the availability various IV-bags and administration devices in the geographic area of interest. For example, IV-bags available in the Europe may not be available in the United States or Japan.
Hold times and storage conditions of the admixture solution will vary depending on the sensitivity of the product. In our experience, clinicians will generally request IV-bag hold times and conditions that provide them with the greatest flexibility in terms of product storage, stability, and administration materials. For many studies, clinical sites would prefer to prepare the solutions in the IV-bag in advance of the administration rather than immediately prior to administration. If there is acceptable physical and chemical stability for the duration of the study, it may be possible to support the maximum allowable beyond-use dating as dictated by USP <797>. However, it may be more appropriate to recommend a shorter hold time in the absence of microbiological testing (e.g. recommending a hold time of 8 hours at room temperature when up to 24 hours is allowed may be allowed) to account for potential excursion [4].
To evaluate admixture compatibility during the duration of the in-use study, generally product quality attributes focused on the active species are monitored. For example, typical assays may include concentration, particulate matter, and aggregate levels (for biologic products) or impurity levels (for small molecule products). Significant changes in these assays may indicate incompatibility of the admixture solution with the diluent or the contact material.
Absent from the assays detailed above is the quantification of leachables in solution. As mentioned previously, excipients in the formulation that are used to help stabilize the drug product and admixture solution may also facilitate leaching from material contact. Extended hold times in the IV-bag and administration times may also facilitate unexpected leaching from the plastic IV containers. However, the presence of leachables from the infusion contact material is often overlooked, especially during early stage product development. For formulations containing excipients that are prone to facilitate leachables, it may be useful to evaluate leachables earlier in the development process to help drive formulation decisions.
Excipients and Leaching: Case study with DEHP
IV-bag and IV-infusion lines were initially constructed using polyvinyl chloride (PVC) plasticized (with 30-40% of bis(2-ethylhexyl) phthalate (DEHP)) [5]. Without the DEHP plasticizer, the PVC is brittle and stiff. PVC+DEHP material, on the other hand, has many characteristics that make it amenable to be the material of construction for IV-bags including collapsibility and transparency [5]. However, since the DEHP is not chemically bonded to PVC, it can leach into the drug solutions, especially those containing non-aqueous components such as fats or surfactants [6].
DEHP has been implicated as a potential carcinogen in rodent studies, though its health impacts on humans are subject to debate [7]. Regardless, the leaching of DEHP from PVC plastics has resulted in concerns due to its potential to cause adverse events in humans [7]. In response, health authorities and organizations have limited the use of DEHP-plasticized PVC. In addition, manufacturers have produced alternative IV-administration materials including PVC plasticized with Tri-2-ethylhexyl trimellitate (TOTM). PVC+TOTM has similar characteristics to PVC+DEHP but the TOTM plasticizer is believed to have lower toxicity and migration rates [8, 9]. Other IV-bag materials include non-PVC options like polyethylene, ethylene vinyl acetate, and polyolefin [4, 5].
Despite the presence of non-DEHP PVC and non-PVC IV-administration materials, PVC+DEHP is still prevalent in the clinical setting. If DEHP leaching is a significant concern, limiting admixture contact material to non-PVC or non-DEHP PVC materials may be an appropriate choice for the admixture storage and administration. The drawback to this approach, however, is that the clinical site may be limited to specific IV-bag and IV-administration materials. Here, we compare the level of DEHP leaching in the presence of common and less common excipients for PVC+DEHP and PVC+TOTM IV-bags to provide an example of how leaching may be controlled by not only appropriate IV-bag material choices but also formulation changes.
The impact of excipient choice on DEHP leaching is illustrated in Figure 1 for PVC+DEHP IV-bags exposed to a placebo solution containing only the excipients polysorbate 80 (PS80), polysorbate 20 (PS20), pluronic F68 (F68), and Solutol HS15® (Solutol) for 72 hours at ambient conditions. PS80, PS20, and F68 are often used in biologic products to enhance stability against physical stresses and Solutol is often used to increase small molecule compound solubility [2, 10]. 
Solutol, PS80, and PS20 all result in the leaching of DEHP from the PVC-DEHP IV-bag, and the concentration of DEHP in the admixture solution increases with exposure time. In contrast, F68 does appear to facilitate any DEHP leaching.
PS80 and PS20 are commonly used in biologic products because these surfactants minimize the interaction of the protein with various interfaces encountered during manufacturing, storage and handling [10]. However, the same properties that stabilize the protein also facilitate the leaching of DEHP from PVC, as shown in Figure 1 [6]. On the other hand F68, a less commonly used excipient, which may provide similar stress protections, delivers a superior DEHP leachables profile with minimal leaching observed at the same concentrations and exposure conditions.
During formulation development, if all three surfactants provide equivalent protection for the protein, then the use of PS20 or F68 may offer the added the benefit of minimizing DEHP leaching, which in turn may allow a clinical site greater flexibility in selecting administration materials. A similar logic may also be applied to small molecule formulation development. For example, during formulation development, if both Solutol and PS20 increase the solubility of a compound equally and the stability profiles are equivalent, the use of PS20 may be preferred over Solutol based on the lower DEHP leachables profile.
As mentioned above, another option to minimize DEHP leaching is to use non-DEHP PVC materials. In Figure 2, we observe that a "nonof DEHP" plasticized PVC still contains low levels of DEHP, and that the residual DEHP will leach into the admixture solution. The presence of low levels of DEHP in TOTM plasticized IV bags is not entirely surprising. TOTM and DEHP have very similar chemical structures, and DEHP is an impurity in the manufacturing process of TOTM [8]. The level of DEHP leaching from the TOTM IV-bags is significantly lower than that observed for PVC plasticized with DEHP. However, if any level of DEHP is of concern, then the choice of excipient that limits DEHP leaching may again provide additional flexibility for clinical administration.
Conclusions
An appropriate experimental design that emulates the clinical administration procedure is important to measure both product inuse stability and potential leachables levels. Strategies to minimize leachables include selecting appropriate administration contact materials and/or formulating the drug product to minimize potential leaching interactions. Both strategies are acceptable and should be based on the product stability profile. In the example discussed here, we show that the choice of excipients may significantly effect the concentration of DEHP in the admixture solution.
While this discussion focused on leachables associated with the admixture and the IV-administration materials, a similar discussion may be applicable to drug product manufacturing and storage. Notably, excipients that are used to increase solubility may also facilitate leaching of less soluble compounds in e.g., fill line tubing [11]. Integration of basic leachables testing early in the formulation development process may help define an appropriate strategy for mitigating risks associated formulations containing excipients that are known to facilitate leachables.
References
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Jason Cheung received Ph.D. in Chemical Engineering from the University of Texas at Austin. He joined Merck & Co. in 2006 and is currently an Associate Principal Scientist in the Bioprocess Development division. He currently leads a group focused on Biophysical Characterization of therapeutic proteins.
Manoj Sharma is an Associate Principal Scientist in the Bioprocess Development division at Merck & Co. in New Jersey. He received his B.Tech. in Chemical Engineering from the Indian Institute of Technology, Delhi, India and his Ph.D. in Chemical Engineering from the City University of New York, New York. He has been working at Merck & Co. since 2005 where he has focused on formulation development of monoclonal antibody candidates for various indications.
Anita Dabbara is a Senior Scientist in Bioprocess Development division at Merck & Co. in Summit, NJ. She received her MS in Chemistry in 1991 from Villanova University. In 1992 she joined Nycomed. While at Nycomed and now at Merck, she has been involved in parenteral formulation development and Biophysical Characterization with a focus on therapeutic monoclonal antibodies and small molecules for over 19 years.
Jonathan Petersen received his BA in Chemistry from Rutgers University. He has over 15 years experience in the pharmaceutical industry, working as an analytical scientist on small molecule active pharmaceutical ingredients and extractables and leachables. He is currently a project analytical chemist working on extractables and leachables at Merck.