A quadruple mixture composed of the corticosteroid dexamethasone, the aminoglycoside antibiotic gentamicin, the vitamin cyanocobalamin (vitamin B12), and the local anesthetic agent procaine, with antimucositis activity. Upon oral administration of the cyanocobalamin/dexamethasone/gentamicin/procaine formulation, the active ingredients prevent or inhibit inflammation and infection of the oral mucosa and reduce the associated pain. This may prevent or treat radiation-induced oral mucositis (OM).