Nalidixic acid is a synthetic narrow spectrum antibacterial. It is bacteriostatic or bactericidal depending on the concentration. Nalidixic acid appears to act by inhibiting bacterial DNA synthesis, possibly by interfering with DNA polymerization. It is rapidly and completely absorbed from the G.I. Tract. Parent drug and active metabolites are distributed to most tissues specially to the kidney and to the urine. During normal renal function, half-life is 1.1 to 2.5 hours and when renal function is impaired, half-life is up to 21 hours. It is rapidly and almost completely excreted within 24 hours.