Monitoring Commercial Ibuprofen Potency Changes Over 1 Year When Stored in a Household Setting

Abstract

Background: Most over-the-counter medications are labeled for storage in a dry, room temperature environment. Despite this, many households store medications in the bathroom, where temperature and humidity extremes may be experienced. Objective: In this project, we sought to investigate the effect that long-term storage in a household bathroom had on potency of over-the-counter ibuprofen (IBU) products as well as on the emergence of a known toxic degradation product, 4-isobutylacetophenone (4-IBP). Methods: A liquid chromatography-tandem mass spectrometry method was developed for the quantitative determination of IBU and 4-IBP in aqueous samples. Three brands each of IBU tablets (200 mg) and suspensions (100 mg/5 mL) were assayed for IBU concentration at the initiation of the study and once monthly thereafter. The samples were stored in a household bathroom, with continuous temperature and humidity monitoring. Each sample was assayed in triplicate and percent recovery was calculated against freshly prepared standards of IBU using bulk powder. Results: Tablets maintained >90% average strength through 3 months, with statistically significant deviation from initial concentration (2-way analysis of variance, P = .05) detected after 6 to 7 months. Suspensions maintained >90% average strength through 5 months, with statistically significant changes from initial concentration emerging after 7 months. After 12 months, the average strength was 73% and 83% for tablets and suspensions, respectively. 4-IBP was not detected in any of the samples during the duration of the study. Conclusions: These data indicate that, while 4-IBP was not detected following 12-month bathroom storage of commercial IBU products, significant changes in potency should negatively affect efficacy.

Introduction

Ibuprofen (IBU) is a nonsteroidal anti-inflammatory drug that possess analgesic, antipyretic, and anti-inflammatory properties, and it was first derived from propionic acid in the late 1960s.^1,2 IBU exerts its pharmacological effects through reversible inhibition of cyclooxygenase-1 and -2 (COX-1, -2), which results in decreased formation of prostaglandin precursors.³ IBU is available over the counter (OTC), and as a prescription, and is widely used for mild to moderate pain, fever reduction, dysmenorrhea, osteoarthritis, and rheumatoid arthritis.⁴ Usual OTC dosing ranges from 200 to 1200 mg a day and can be increased for prescription use to 3200 mg.⁵ Since IBU first became available OTC in 1984, sales have more than tripled, with 40% of households owning IBU and 17% of adults endorsing weekly IBU use.^6-8

In view of IBU’s widespread use, extensive consumption, and availability as an OTC product, it is relevant to understand how this product is stored. Monographs for correct IBU storage state to avoid excessive heat (above 104°F), excessive humidity, and to store at controlled room temperature (between 68°F and 77°F).⁹ In households, it is a common practice to store medications in bathrooms, which provides a moist, humid environment that can facilitate the degradation process of medications.¹⁰ A recent survey found that a large percentage of patients are not informed regarding proper medication storage, with almost half of patients surveyed improperly storing their medications.¹¹ Several methods have been described in the literature of accelerated degradation of IBU utilizing high-performance liquid chromatography (HPLC) methods for quantification and analysis of the chemical stability. IBU is sensitive to oxidative¹² and photolytic^13,14 degradations, which, following a radical mechanism, yield several products.^15,16 One such product, 4-isobutylacetophenone (4-IBP), has been shown to be genotoxic¹⁷ and toxic to fibroblasts both in vivo and in vitro.¹⁸ The US Food and Drug Administration has placed a limit of 4-IBP to ≤0.1% (wt/wt IBU) in both tablets and oral liquids.¹⁹

The purpose of this study was to investigate the potential for IBU degradation, and the subsequent manifestation of 4-IBP, when product tablets and suspensions were stored in “household bathroom” conditions for a period of 1 year. The US Pharmacopeia (USP) has historically established 90% to 110% potency as acceptable, allowing for ±10% as a range for stability investigations.²⁰ This study involved the development and validation of a simple, sensitive, and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of IBU and 4-IBP in tablets and suspensions. Chemical structures of IBU and 4-IBP can be seen in Figure 1.

Figure 1.

Mass chromatogram of ibuprofen (m/z 205.09, −ESI) and 4-isobutylacetophenone (m/z 177.15, +ESI) with chemical structures.

Methods

Instrumentation and Materials

A Shimadzu HPLC System with XR upgrade was used for all chromatographic measurements (Shimadzu Scientific, Kyoto, Japan). The system was equipped with column oven, in-line degasser, and autosampler. Separation was achieved utilizing a UCT C₁₈ column (2.1 × 100 mm; 1.8 µm; Bristol, PA). The separation with LC-MS grade acetonitrile (ACN; organic phase) and LC-MS grade water (aqueous phase) was run in 15:85 A:B isocratic mode (Fisher Scientific, Waltham, MA). For mass spectrometric detection, IBU was ionized in negative electrospray mode (−ESI) using m/z 205.09 and 4-IBP in +ESI mode at m/z 177.15, using liquid nitrogen as the nebulizing gas (1.5 L/min). Source temperature was maintained at 200°C and detector voltage at 1.85 kV. An example mass chromatogram is shown in Figure 1. Hydrochloric acid was used during sample preparation (Fisher Scientific, Waltham, MA), and calibration solutions were prepared using a USP-grade reference standard of IBU (MP Biomedicals, Solon, OH, Lot QR12429) and 4-IBP (> 97%, Acros Organics, Waltham, MA), which were stored in a controlled laboratory environment: room temperature 20°C to 25°C and refrigerated 2°C to 8°C. Calibration curves were created in the ranges of 0.1 to 2 mg/mL (IBU) and 2 to 100 µg/mL (4-IBP). Three brands each of IBU tablets (200 mg) and suspensions (100 mg/5 mL) were purchased and assayed for IBU concentration at the initiation of the study. Characteristics of each dosage form are summarized in Table 1. The samples were stored in a household bathroom, while temperature and humidity were continuously recorded using EXTECH Instruments RHT10 humidity/temperature datalogger Model No. 170314406 (Nashua, NH).

Table 1.

Identification and Description of Dosage Forms.

Product	Description (Dose)	Excipients Known to Accelerate Ibuprofen Degradation	Expiration
Tablet Brand A	Red-brown (200 mg)	Povidone	December 2020
Tablet Brand B	Orange (200 mg)	Polyethylene glycol (PEG)	August 2019
Tablet Brand C	White (200 mg)	PEG, povidone, and hypromellose	November 2020
Suspension Brand A	Purple (100 mg/5 mL)	Polysorbate 80	June 2020
Suspension Brand B	Purple (100 mg/5 mL)	Polysorbate 80	December 2020
Suspension Brand C	Colorless (100 mg/5 mL)	Polysorbate 80	January 2020

LC-MS Method

Initial mass transitions for IBU and 4-IBP were determined by flow injection analysis, and dwell time and collision energy were optimized for each channel. For each day of analysis, a series of IBU calibration samples were prepared by digesting the USP-grade reference standard in 60:40 0.01 M HCl–ACN to form a stock solution of 20 mg/mL, and then diluting it to the calibration concentrations (0.1-2 mg/mL) using methanol. This sample preparation was adapted from Cory et al.¹⁴ On each day of the stability investigation, a full calibration curve of IBU was prepared and analyzed, with target R² > 0.99. Additionally, reference standards of 4-IBP were analyzed (2 µg/mL) to ensure continued integrity of the +ESI m/z 177.15 channel. The precision of the method, as reflected by percent relative standard deviation (%RSD), and accuracy, as reflected by percent error, was monitored on the 2 mg/mL and 0.2 mg/mL IBU standards throughout the duration of the study (n = 60 data points). Finally, full-scan MS data (m/z 50-300) were collected in +ESI and −ESI modes for each sample and calibration injection. These data were compared using Mass Profiler (Shimadzu, Kyoto, Japan) to identify additional ions that are associated with known degradation products.^14,16

Stability Investigation

The stability investigation continued for a period of 12 months (May 2018 to April 2019). The storage setting (“household bathroom”) was located in a 2-person household in the Southeast region of the United States, with central heat and air conditioning, maintaining average home temperature of 68°F to 72°F. The products were stored in their original containers, and tablets/aliquots removed and transferred to 15-mL capped plastic tubes for transport to the laboratory. Three (200 mg) tablets (A, B, C) were removed from each bottle, and three 5-mL aliquots were removed from each suspension (A, B, C; 100 mg/5 mL), for analysis every 30 days. The USP-grade reference standard was digested in 60:40 0.01 M HCl–ACN to form a stock solution of 20 mg/mL, and then diluted to appropriate concentrations (2.0, 1.0, 0.5, 0.2, 0.1 mg/mL) using methanol. Both tablets (A, B, C) and suspensions (A, B, C) were digested in 40:60 0.01 M HCl–ACN using 1-hour sonication to achieve a stock concentration of 20 mg/mL and diluted to assay concentrations of 2 mg/mL for tablets and 0.2 mg/mL for suspensions using methanol. Tablets, suspensions, and the USP-grade reference standard dilutions were filtered through a 0.22-µm polytetrafluoroethylene membrane into HPLC vials for analysis. Each sample was assayed in triplicate (n = 9 for each sample set) and percent recovery was calculated against freshly prepared IBU reference standards. The concentration-versus-time profiles for both IBU tablets and suspensions were evaluated using a 2-way analysis of variance with Sidack’s multiple comparison test (P = .05) using Graph Pad Prism, version 7.04 (La Jolla, CA).

Results

The LC-MS/MS method was linear in the range of 0.1 to 2 mg/mL for IBU. Furthermore, an assessment of the precision and accuracy of the assay concentrations (2 and 0.2 mg/mL) yielded a %RSD and % error <10% for the study duration. More specifically, the %RSD for 2 mg/mL and 0.2 mg/mL was 8.81% and 7.75%, respectively. Percent error was 7.81% for the high assay concentration and 6.38% for the low concentration. These data reflect n = 60 data points, collected over the 1-year study duration.

Over the duration of the study, the average storage temperature was 69.2 ± 3.7°F with a range of 59.9°F to 86.2°F. The average relative humidity was 63.2 ± 14.9% with a range of 29.2% to 100%. The total number of times the temperature exceeded the upper limit of the recommended storage setting (77°F) was 753 times, which represents 0.72% of the data points collected. The number of times the relative humidity exceeded 70%, adapted from Cory et al, was 9394 times, representing 8.98% of the data points.¹⁴ Fluctuations in both temperature and humidity for storage setting can be viewed in Figure 2. Months 1 and 5 saw spikes in the number of times the temperature exceeded recommended storage, and month 9 spiked the number of data points where humidity >70% was documented.

Figure 2.

Fluctuations in storage temperature and humidity for ibuprofen products over 12 months. Graphs represent the number of data points exceeding temperature (>77°F) and relative humidity (>70%) thresholds.

All IBU products investigated fell below 90% product potency during the duration of the 12-month study. Tablets maintained acceptable product potency (range: 90% to 110%) through 3 months. Statistically significant changes in potency as determined by a 2-way analysis of variance, P = .05, were detected after 6 to 7 months. Linear regression analysis was used to model the discrete time for the tablets to fall below 90% potency. Tablet A fell below 90% potency at 4.13 months (R² = 0.3878), tablet B at 3.71 months (R² = 0.5494), and tablet C at 4.84 months (R² = 0.1741). After 12 months of storage, the average tablet strength was 73.3% of the initial potency. These data are graphically summarized in Figure 3.

Figure 3.

Graphical representation of potency change seen in OTC ibuprofen tablets and suspensions stored in household bathroom conditions for 12 months. Each data point shows average recovery (n = 9) and error bars reflect standard deviation.

Suspensions maintained acceptable average product potency through 5 months with statistically significant changes versus the initial concentration emerging after 7 months. Linear regression analysis revealed a discrete time of potency <90%; suspension A was 5.72 months (R² = 0.3241), suspension B at 6.73 months (R² = 0.3734), and suspension C at 7.49 months (R² = 0.2610). After 12 months of storage, the average suspension strength was 82.8% of initial potency. These data are summarized in Figure 3.

The 4-IBP was not detected in the calibration range in any of the product samples during the duration of the study. Mass profiling experiments of the products on the final sampling day (360) yielded some evidence of an additional degradant (+ESI, m/z 179.21) in tablets consistent with 1,4-isobutylphenyl ethanol, reported previously from thermal degradation of IBU.¹⁶

Discussion

Several investigators have documented that IBU, when exposed to temperature and humidity extremes, will degrade and subsequently manifest several byproducts.^14,16,21,22 To our knowledge, this is the first time an experiment has been carried out storing and monitoring IBU in a normal household setting, namely, a bathroom medicine cabinet exposed to normal day-to-day temperature and humidity fluctuations. Over the course of the study, none of the products expired; it may be noted that in other studies expired products were used and potentially could have contributed to IBU instability.¹⁴ Although the toxic compound 4-IBP was not identified in any of the products, all products lost potency over the duration of the study with sharp declines (see Figure 3) occurring during months 6 and 7. Extremes in temperatures rarely occurred in the storage setting with temperatures recorded never exceeding 90°F; however, the relative humidity in the storage setting exceeded 70% relative humidity in many instances, also remaining above 90% relative humidity for significant periods of time. Of note, this burst of degradation also followed a spike in temperature recording of >77°F noted in month 5. Despite being in a climate-controlled home, the spikes of temperature and humidity in the bathroom are inevitable, and especially pronounced when the outside temperatures rise. In this experiment, month 5 corresponds to September.

Excipients theorized to accelerate degradation of IBU products are polyethylene glycol (PEG), povidone, hypromellose, and polysorbate 80.¹⁴ Tablet A contained povidone, tablet B contained PEG, while tablet C contained as PEG, povidone, and hypromellose. All suspensions (A-C) contained polysorbate 80. Excipients found in the products may contribute to their overall degradation and thus reduction in potency; however, no apparent trend was identified in this study with regard to which products’ degradation was accelerated due to particular excipients.

This study was limited by single batches of each product test, and monitoring for degradation products was largely restricted to 4-IBP. Additionally, we began the investigation in April, and thus experienced the warmest months of the year at the beginning of the study. The purpose of this study was not to assign a new beyond-use-date for OTC IBU products, but rather to draw attention to the importance of drug products storage as it relates to potency maintenance. The potency changes we saw over a 1-year period would be clinically significant, and indicate IBU’s sensitivity to fluctuations in temperature and humidity that exceed the storage recommendations.

Conclusion

Pharmacists are easily accessible health care providers and play a crucial role in their community, counselling patients on their medications. This role is important in ensuring patient safety and product efficacy for both prescription and OTC medications. In this study, we found that storage of OTC IBU products in a household bathroom, which is common for many patients, can compromise product potency. Therefore, patient counseling on proper medication storage may be an important piece of the overall community pharmacist-patient interaction, with the goal of maintaining product integrity and ultimately improving patient outcomes.