Synergistic Antimicrobial and Antioxidant Properties of <b><i>Coccinia grandis</i></b> (L.) Voigt, <b><i>Clerodendrum inerme</i></b> (L.) Gaertn. and <b><i>Acanthus ebracteatus</i></b> Vahl. Extracts and Their Potential as a Treatment for Xerosis Cutis

<b><i>Background:</i></b> A common health condition among older persons is xerosis cutis. Topical corticosteroid treatments are ­associated with side effects. There is an unmet need for her­bal treatment alternatives. <i>Coccinia grandis</i>, <i>Clerodendrum inerme</i> and <i>Acanthus ebracteatus</i> are used to treat skin con­ditions in Thai traditional medicine. This study aimed to investigate their antimicrobial and antioxidant properties, synergistic properties as well as their cytotoxicity. <b><i>Methods:</i></b> ­Ethanolic herbal extracts were used to perform minimal ­inhibitory (MIC) and minimal bactericidal concentration (MBC) assays on common skin pathogens. Synergistic anti­microbial activity was evaluated by a chequerboard assay. Antioxidant and synergistic properties were assessed by a 1,1-diphenyl-2-picrylhydrazyl assay. Cytotoxicity was tested on normal adult human primary epidermal keratinocytes. <b><i>Results:</i></b> All extracts showed an inhibitory effect on growth of all microorganisms tested. MIC and MBC values ranged from 0.0625 to 32 mg/mL and from 0.0625 to &#x3e;256 mg/mL, respectively. <i>A. ebracteatus</i> extract markedly demonstrated bactericidal activity against an methicillin-resistant <i>Staphylococcus aureus</i> strain. Additive antimicrobial activity was observed (fractional inhibitory concentration index values: 0.75–1). All extracts possessed antioxidant properties (IC₅₀ values: 0.12–0.25 mg/L). However, antagonism was observed with paired extract combinations (combination index values: 1.025–1.455). The cell viability assay confirmed that herbal extracts were not cytotoxic. <b><i>Conclusions:</i></b> Our results provide early findings of pharmacological activities to support a novel choice of herbal combinations as potential local skin treatment options for xerosis cutis.