Flucloxacillin is a weak inducer of CYP3A4 in healthy adults and 3D spheroid of primary human hepatocytes

Ditte B Iversen, Ann-Cathrine Dalgård Dunvald, Daniel M Jespersen, Flemming Nielsen, Kim Brøsen, Per Damkier, Helen S Hammer, Oliver Pötz, Erkka Järvinen, Tore B Stage

Research output: Contribution to journalJournal articleResearchpeer-review


Flucloxacillin is a widely used antibiotic. It is an agonist to the nuclear receptor PXR that regulates the expression of cytochrome P450 (CYP) enzymes. Treatment with flucloxacillin reduces warfarin efficacy and plasma concentrations of tacrolimus, voriconazole, and repaglinide. We conducted a translational study to investigate if flucloxacillin induces CYP enzymes. We also investigated if flucloxacillin induces its own metabolism as an autoinducer. We performed a randomized, unblinded, two-period, cross-over, clinical pharmacokinetic cocktail study. Twelve healthy adults completed the study. They ingested 1 g flucloxacillin 3 times daily for 31 days, and we assessed the full pharmacokinetics of the Basel cocktail drugs on days 0, 10, and 28, and plasma concentrations of flucloxacillin on days 0, 9, and 27. The 3D spheroid of primary human hepatocytes (PHHs) were exposed to flucloxacillin (concentration range: 0.15–250 μM) for 96 hours. Induction of mRNA expression, protein abundance, and enzyme activity of CYP enzymes were assessed. Flucloxacillin treatment reduced the metabolic ratio of midazolam (CYP3A4), (geometric mean ratio (GMR) 10 days (95% confidence interval (CI)): 0.75 (0.64–0.89)) and (GMR 28 days (95% CI): 0.72 (0.62–0.85)). Plasma concentrations of flucloxacillin did not change during 27 days of treatment. Flucloxacillin caused concentration-dependent induction of CYP3A4 and CYP2B6 (mRNA, protein, and activity), CYP2C9 (mRNA and protein), CYP2C19 (mRNA and activity), and CYP2D6 (activity) in 3D spheroid PHH. In conclusion, flucloxacillin is a weak inducer of CYP3A4, which may lead to clinically relevant drug–drug interactions for some narrow therapeutic range drugs that are substrates of CYP3A4.

Original languageEnglish
JournalClinical Pharmacology and Therapeutics
Issue number2
Pages (from-to)434-445
Publication statusPublished - Aug 2023

Bibliographical note

This article is protected by copyright. All rights reserved.


  • Adult
  • Cytochrome P-450 CYP3A/genetics
  • Cytochrome P-450 Enzyme System/metabolism
  • Drug Interactions
  • Floxacillin/pharmacology
  • Hepatocytes/metabolism
  • Humans
  • RNA, Messenger


Dive into the research topics of 'Flucloxacillin is a weak inducer of CYP3A4 in healthy adults and 3D spheroid of primary human hepatocytes'. Together they form a unique fingerprint.

Cite this