In vitro activity of BRL 36650, a new semisynthetic penicillin.

BRL 36650 [sodium 6 beta-(D-2-[(4-ethyl-2, 3-dioxopiperazin-1-yl)carbonylamino]-2-(3,4-dihydroxyphenyl) acetamido)-6 alpha-formamido-penicillinate] is a new semisynthetic penicillin. It was tested in vitro for activity against 884 organisms cultured from blood specimens of cancer patients. BRL 36650 had broad-spectrum activity against the gram-negative bacilli tested but had no gram-positive activity. The MIC against 90% of the Pseudomonas aeruginosa isolates was 3.12 micrograms/ml. The activity of BRL 36650 was superior to that of piperacillin, comparable or slightly inferior to that of aztreonam and ceftazidime, and lower than that of imipenem and amifloxacin. BRL 36650 should prove useful for the management of gram-negative bacillary infections, including those caused by P. aeruginosa.