Actions: Cycloserine inhibits cell wall synthesis in susceptible strains of Gram-positive and Gram-negative bacteria and in Mycobacterium tuberculosis. Indications. Cycloserine is indicated in the treatment of active pulmonary and extra-pulmonary tuberculosis (including renal disease) when the organisms are susceptible to this drug and after failure of adequate treatment with the primary medications (streptomycin, isoniazid, rifampicin and ethambutol). Like all anti-tuberculous drugs, cyclosenne should be administered in conjunction with other effective chemotherapy and not as the sole therapeutic agent. Cycloserine may be effective in the treatment of acute urinary tract infections caused by susceptible strains of Gram-positive and Gram-negative bacteria, especially Klebsiella/Enterobacter species and Escherichia coli. It is generally no more and may be less effective than other antimicrobial agents in the treatment of urinary tract infections caused by bacteria other than mycobacteria, Use of cycloserine in these infections should be considered only when the more conventional therapy has failed and when the organism has been demonstrated to be sensitive to the drug.