A new metallo-.beta.-lactamase inhibitor which acts as amedicament for inhibiting the inactivation of .beta.-lactamantibiotics and recovering anti-bacterial activities is disclosed.The maleic acid derivatives having the general formula (I) havemetallo-.beta.-lactamase inhibiting activities. It is possible torecover the anti-bacterial activities of .beta.-lactam antibioticsagainst metallo-.beta.-lactamase producing bacteria by combiningthe compound of the general formula (I) with .beta.-lactamantibiotics.(see formula I)
