acid derivs. of formula (I) and their salts with bases and/or acids are new: In formula (I), R1 is 1-5C alkyl, and R2 is 1-imidazolyl or a gp. -O(CH2)m-OR3, -O(CH2)n-CHR4-OR3 or -OCHR4-(CH2)n-OR3 in which R3 is H of 1-5C alkyl, R4 is 1-5C alkyl, m is 2, 3 ro 4 and n is 1, 2 or 3. (I) are antibacterials, esp. against gram-negative bacteria, and show a high degree of urinary excretion (6% or more of an oral dose of 100 mg/kg is excreted via the urine within 6 hrs. in the rat). They are partic. useful as urinary tract antibacterials. A spacific cpd. (I) is 1-ethyl-7-(2-methoxyethoxy)-4-oxo-1,4-dihydro-1,6-naphthyridine-3- -carboxylic acid. This is prepd. e.g. from 1-ethyl-7-bromo-4-oxo-1,4-dihydro-1,6-naphthyridine-3-carboxylic acid, NaH/oil and 5 ml 2-methoxyethanol.
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