Description:
<jats:title>Abstract</jats:title><jats:p>The aim of this study was to characterize the antioxidant activity of penicillin G (PG), ampicillin (AMP), oxacillin (OX) and dicloxacillin (DOX) through their reactivity towards reactive oxygen species (superoxide anion radical,
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/bio3199-math-0001.png" xlink:title="urn:x-wiley:15227235:media:bio3199:bio3199-math-0001" />; hydroxyl radical, HO<jats:sup>•</jats:sup>; peroxyl radical, ROO<jats:sup>•</jats:sup>; hydrogen peroxide, H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>; DPPH<jats:sup>•</jats:sup>) using various <jats:italic>in vitro</jats:italic> antioxidant assays with chemiluminescence (CL) and spectrophotometry as measurement techniques. In hydroxyl radical assays , PG, OX and AMP were found to inhibit the CL signal arising from the Fenton‐like reaction in a dose‐dependent manner with IC<jats:sub>50</jats:sub> = 0.480 ± 0.020 mM, IC<jats:sub>50</jats:sub> = 0.569 ± 0.021 mM, and IC<jats:sub>50</jats:sub> = 0.630 ± 0.019 mM, respectively. The highest reactivity of PG among the tested penicillins towards the HO radical was confirmed in the deoxyribose degradation assay. In the ABAP‐derived ROO radical assay, the radical‐scavenging ability of the test penicillins was in the following order: AMP > PG > DOX > OX. The number of reduced DPPH radicals by the drugs tested was <1 being the biggest for PG. The weak antioxidant capacity of the test penicillins was confirmed in the trolox antioxidant capacity assay (0.075 ± 0.004; 0.093 ± 0.006; 0.123 ± 0.005; 0.126 ± 0.004) for OX, AMP, DOX, PG, respectively. Use of luminol as a CL probe for estimation of penicillin reactivity towards H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> showed that only AMP was able to quench light emission; the remaining antibiotics demonstrated a strong enhancing effect. All the examined compounds showed a weak antioxidant potential when estimated using the ferric‐ferrozine assay. This study is the first to report the evaluation of test penicillins as antioxidants under the same reaction conditions.</jats:p>