A heterocyclic oxophthalazinyl acetic acid having aldose reductase inhibitory activity of the formula
wherein X is oxygen or sulfur, Z is a covalent bond, O, S, NH or CH₂ or CHR₅Z is vinylene; R₁ is hydroxy, or a prodrug group; R₂ is a heterocyclic group, R₃ and R₄ are hydrogen or the same or a different substituent, and R₅ is hydrogen, methyl or trifluoromethyl. The pharmaceutically acceptable acid addition salts of the above compounds wherein R₁ is di(C₁-C₄)alkylamino or (C₁-C₄)alkoxy substituted by N-morpholino or di(C₁-C₄)alkylamino and the pharmaceutically active base addition salts of the above compounds wherein R₁ is hydroxy are also aldose reductase inhibitors.
A heterocyclic oxophthalazinyl acetic acid having aldose reductast inhibitory activity of the formula ##STR1## wherein X is oxygen or sulfur; Z is a covalent bond, O, S, NH or CH.sub.2 or CHR.sub.5 Z is vinyl; R.sub.1 is hydroxy, or a prodrug group; R.sub.2 is a heterocyclic group, R.sub.3 and R.sub.4 are hydrogen or the same or a different substituent, and R.sub.5 is hydrogen, methyl or trifluoromethyl. The pharmaceutically acceptable acid addition salts of the above compounds wherein R.sub.1 is di(C.sub.1 -C.sub.4)alkylamino or (C.sub.1 -C.sub.4)alkoxy substituted by N-morpholino or di(C.sub.1 -C.sub.4)alkylamino and the pharmaceutically active base addition salts of the above compounds wherein R.sub.1 is hydroxy are also aldose reductase inhibitors.