An in vitro evaluation of clavulanic acid, a potent, broad-spectrum beta-lactamase inhibitor.

The in vitro efficacy of clavulanic acid, a new broad-spectrum inhibitor of enterobacterial beta-lactamases, was investigated. In conventional agar dilution tests, the presence of a sub-inhibitory level of clavulanic acid (8 microgram/ml) lowered the minimum inhibitory concentration of ampicillin for many resistant enterobacteria to therapeutically achievable levels. When tested against dense populations of Escherichia coli and klebsiella strains in a static turbidimetric system and in an in vitro model of the treatment of bacterial cystitis, clavulanic acid plus ampicillin suppressed bacterial growth for periods far exceeding the normal interdose interval at concentrations at which neither agent alone was effective. In addition to its activity as a beta-lactamase inhibitor, clavulanic acid may interact with other beta-lactam antibiotics in a second, distinct way. Because of this synergic interactions may occur with non-beta-lactamase producing organisms, and the overall synergic effect obtained with beta-lactamase producers may be compounded of two separate elements.