Screening trimethoprim primary metabolites for covalent binding to albumin


Modification of endogenous proteins by drugs and drug metabolites are thought to be a cause of idiosyncratic adverse drug reactions (IADRs). Trimethoprim (TMP) is a commonly prescribed antibiotic that has been implicated in IADRs; however, there is no known mechanism by which this drug or its metabolites modify proteins. This study describes the results of screening trimethoprim and its primary metabolites for the ability to covalently modify human serum albumin (HSA). The first step of the screen was in vitro reactions of the compounds with HSA followed by western blotting with antisera specific to drug-modified proteins. Compounds with positive signal in the western blot were then screened using an untargeted peptide profiling method to discover modified peptides. This strategy identified two sites in HSA that are modified by incubation with a TMP metabolite, α-hydroxy trimethoprim (Cα-OH-TMP).

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idiosyncratic adverse drug reactions


human liver microsomal




1-N-oxide trimethoprim


3-N-oxide trimethoprim






α-hydroxy trimethoprim


carbamazepine 10,11-epoxide


human serum albumin


keyhole limpet hemocyanin


liquid chromatography mass spectrometry


extracted ion chromatogram


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We would like to thank Robert Hanzlik and Yakov Koen at the University of Kansas, Department of Medicinal Chemistry, for their assistance in TMP antigen generation and antisera dilution and inhibition work. This work was supported by the National Institutes of Health R01GM129783 (J.L.G).

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Correspondence to Jennifer L. Goldman.

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Nolte, W.M., Tessman, R.T. & Goldman, J.L. Screening trimethoprim primary metabolites for covalent binding to albumin. Med Chem Res 29, 1238–1246 (2020).

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  • Trimethoprim
  • Metabolism
  • Protein adduct
  • Adverse drug reaction