REGULAR ARTICLE Chiral bioanalytical methods in bioequivalence studies of intravenous vs. oral formulations of ibuprofen Esperanza González-Rojano 1 | Julio Marcotegui 2 | Leonor Laredo 1,3 | Luther Gwaza 4 | John Gordon 5 | Antonio Portolés 1,3 | Emilio Vargas 1,3 | Susana Morales-Alcelay 6 | Alfredo García-Arieta 6 1 Clinical Pharmacology Department, Hospital Clínico San Carlos, IdISSC, Madrid, Spain 2 Department of Anaesthesiology, Reanimation and Pain Treatment, Hospital Clínico San Carlos, Madrid, Spain 3 Pharmacology and Toxicology Department, Complutense University of Madrid, Spain 4 Department of Essential Medicines and Health Products (EMP), World Health Organization, Geneva, Switzerland 5 Division of Biopharmaceutics Evaluation, Bureau of Pharmaceutical Sciences, Therapeutic Products Directorate, Health Canada, Ottawa, Canada 6 Division of Pharmacology and Clinical Evaluation, Department of Human Use Medicines, Spanish Agency for Medicines and Health Care Products, Madrid, Spain Correspondence Alfredo García-Arieta, Division of Pharmacology and Clinical Evaluation, Department of Human Use Medicines, Spanish Agency for Medicines and Health Care Products, C/Campezo 1, Edificio 8, 28022. Madrid, Spain. Email: agarciaa@aemps.es Abstract According to the Ibuprofen Product-Specific Bioequivalence Guidance of the European Medicines Agency, achiral bioanalytical methods are considered acceptable for demonstration of bioequivalence of ibuprofen-containing products. The aim of this investigation is to compare the bioequivalence outcomes obtained with individual R and S ibuprofen enantiomers and the sum of both enantiomers from bioequivalence studies in which new intravenous ibuprofen products were compared with oral ibuprofen products. Bioequivalence was assessed for S and R enantiomers of ibuprofen and the sum of both enantio- mers, which was calculated to represent the results that would have been obtained with an achiral assay. The infusion rates of 15, 20, and 30 minutes modify the maximum concentration (C max ) of the intravenous administrations. In contrast, the time when the maximum concentration is observed (T max ) was insensitive to detect differences in input rate within this range of infusion times. The eutomer S-ibuprofen is the least sensitive analyte to detect differ- ences in input rate; therefore, the regulatory acceptance of achiral bioanalytical methods for ibuprofen bioequivalence studies is justified because the sum of both enantiomers is more discriminative than the chiral methods where only the eutomer is used for regulatory decisions. KEYWORDS bioequivalence, enantiomer, intravenous, R-ibuprofen, S-ibuprofen 1 | INTRODUCTION Ibuprofen is an analgesic and anti-inflammatory racemic drug that contains equal amounts of R(-)-ibuprofen and S(+)-ibuprofen (Figure 1). The S(+) enantiomer is the active compound because it exhibits about 160 times more potency than the R(-)-ibuprofen in the in vitro inhibition of prostaglandins synthesis. 1,2 Racemic ibupro- fen has half the potency of S(+)-ibuprofen in inhibiting platelet aggregation and thromboxane formation, since R(-)-ibuprofen is about 2 orders of magnitude less active. 3 Ex vivo studies of thromboxane generation in clotting blood also found S(+)-ibuprofen to be twice as potent as the racemate. 4 These differences go so far that some authors think that R and S-ibuprofen should be Additional Authorship Options: Esperanza González-Rojano and Julio Marcotegui should be considered joint first author. Received: 28 April 2020 Revised: 3 June 2020 Accepted: 4 June 2020 DOI: 10.1002/chir.23258 Chirality. 2020;1–9. wileyonlinelibrary.com/journal/chir © 2020 Wiley Periodicals LLC. 1