Se investiga la actividad antibacteriana de soluciones de las quinolonas ácido nalidíxico, ciprofloxacino y levofloxacino irradiadas mediante luz UVA. La fotólisis de las quinolonas produce una disminución de la actividad antibacteriana en cepas de E.coli y de S.aureus, evidenciándose un aumento de la concentración mínima inhibitoria de un 50% frente a las cepas ensayadas, en relación a las quinolonas no irradiadas. Se postula un mecanismo fotolítico radicalario con la consecuente fotodegradación de la porción γ-piridona-β-carboxílica responsable de la actividad antibacteriana.

Palabras clave: Quinolonas. Fotolisis. CMI. Fotodegradación.

The antibacterial activity of UVA-irradiated solutions of nalidixic acid, ciprofloxacin and levofloxacin was investigated. Photolysis of quinolones produced a decrease in antibacterial activity in strains of E. coli and S. aureus, becoming manifest through an increase of 50% in the minimum inhibitory concentration of the drug as compared to nonirradiated quinolones. In this study, it is suggested that a radical-mediated photolytic mechanism exists, leading to the photodegradation of the γ-piridone- β-carboxylic group, which is the mediator that is responsible for the drugs antibacterial activity.

Key words: Quinolones. Photolysis. MIC. Photodegradation.