(M0930-02-09) Revealing the Stable δ²H, δ¹³C, and δ¹⁸O Isotopic Patterns of Ibuprofen Drug Products and Commonly used Pharmaceutical Excipients

Purpose: In 2024, a total of 3.4 trillion defined daily doses of prescription and over-the-counter medicines were distributed globally [1]. The World Health Organization reported in 2017 that 10.5% of all drugs in low- and mid-income countries are substandard or falsified medical products, with an estimated US$ 30.5 billion in spending, adjudging the urgency of addressing the public health and socioeconomic problem of growing substandard and falsified medical products infiltrating the market [2, 3]. Isotopic ratio mass spectrometry (IRMS) is efficient for high-precision stable and radiogenic isotopic measurements. For decades, stable light isotopes analysis, e.g.,δ²H,δ¹³C, andδ¹⁸O, has been used as an approach in biogeochemistry and food science to understand a variety of geological processes and utilized in controlling the safety, quality, authenticity, and traceability of food products, respectively [3-8]. Despite IRMS being a powerful tool for identifying unique isotopic patterns and demonstrating a high level of accuracy and specificity, the isotopic methodology has oddly not been adapted as a pharmaceutical application to the latest versions of either the European Pharmacopoeia or the United States Pharmacopeia [9, 10]. This project explored the use of stable light δ²H, δ¹³C, and δ¹⁸O isotopic ratio mass spectrometry (IRMS) analysis to i) identify unique isotopic signatures of solid drug products and commonly used excipients, ii) investigate the isotopic signal stability across pharmaceutical batches from the same manufacturer, and iii) to identify the unique isotopic signature of pharmaceutical components to explore the potential of implementing IRMS analysis in pharmaceutical science.

Methods: 27 ibuprofen drug products were collected from six different countries with various sample matrix complexities having active pharmaceutical ingredient varying from 20-82% of the total tablet mass and 6-18 excipients. Based on the ibuprofen drug formulation strategies, 27 of the most common excipients were selected for IRMS analysis. Unlike most analytical methodologies, the IRMS sample preparation was limited to homogenizing the drug products by ball milling prior to analysis. Approximately 150 µg of sample material was encapsulated (n=3) and analyzed through TC/EA IRMS calibrated against certified reference materials.

Results: The isotopic analyses were conducted over consecutive weeks with high data reproducibility. Expectedly and comparable to previous studies in biogeochemistry and food science, the lowest isotopic variation was observed for the δ¹³C signal, followed by δ¹⁸O and δ²H for both the ibuprofen drug products and excipients. The isotopic standard deviations for the drug products (δ²H ≤5.29‰, δ¹³C ≤0.37‰, and δ¹⁸O ≤1.75‰) were expectedly higher compared to mono-ingredient excipients but generally considered low. Unique isotopic signatures were determined for the drug products and excipients, and through the isotopic separation, it was possible to differentiate across pharmaceutical manufacturers and between drug products containing various API doses produced by the same manufacturer. The isotopic signal stability across pharmaceutical batches was determined through analysis (n=3) of 9 drug products obtained from the same manufacturer, having different batch numbers, expiration dates, and packaging material. The isotopic variation (δ²H -44.78±3.51‰, δ¹³C -22.20±0.20‰, and δ¹⁸O 33.59±1.75‰) within batches from a pharmaceutical manufacturer was lower than the isotopic variation across the different drug products.

Conclusion: This comprehensive study presented how stable light δ²H, δ¹³C, and δ¹⁸O analysis allowed robust, specific, and direct analysis of drug products and excipients only using ~150 µg of sample. The 27 drug products demonstrated unique isotopic signatures related to the drug formulation and production strategies of the individual manufacturers. Homogenization of drug products prior to isotopic analysis expectedly resulted in higher isotopic standard deviations than for mono-ingredient excipients. However, for both the ibuprofen drug products and excipients, δ¹³C had the lowest isotopic variation by mass, followed by δ²H and δ¹⁸O. The isotopic stability was evaluated for 9 batches from the same manufacturer and had lower variation within the 9 batches than across the 27 drug products. Stable light isotopic analysis, thus, is a powerful tool for health authorities and pharmaceutical manufacturers to detect falsified and substandard drug products, protect against patent infringement, and evaluate raw material supply lines to ensure high-quality products

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8. Liu, H.; Nie, J.; Liu, Y.; Wadood, S. A.; Rogers, K. M.; Yuan, Y.; Gan, R. Y. A Review of Recent Compound-Specific Isotope Analysis Studies Applied to Food Authentication. Food Chem 2023, 415.
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10. EDQM Council of Europe. European Pharmacopoeia 11.8. European Pharmacopoeia 11.8. 2025.

Acknowledgements: The authors gratefully acknowledge the Novo Nordisk Foundation (Grant number NNF23OC0082920) and The Steven and Roberta Denning International Research Fund VPDoR International Research Exploration Seed Grant for financial support of this research. Part of this work was performed in the Stanford Isotope Geochemistry Measurement and Analysis Facility with support from the Stanford Doerr School of Sustainability and Stanford Nano Shared Facilities (SNSF)/Stanford Nanofabrication Facility (SNF) under National Science Foundation award ECCS-2026822, RRID: SCR_023259.


Distribution of 𝛿2H, 𝛿13C, and 𝛿18O isotopic values for 9 different Advil batches, 27 drug products, and 27 common excipients used in drug production of ibuprofen tablets. Note the different y-axis values.


3D presentation of the 𝛿2H, 𝛿13C, and 𝛿18O isotopic measurements of 27 drug products and pure ibuprofen color-coded according to the country of purchase.


3D presentation of the 𝛿2H, 𝛿13C, and 𝛿18O isotopic measurements of 27 common pharmaceutical excipients color-coded according to the chemical compound.