The disclosure relates to pyridazinone derivative compounds of formula (I): and pharmaceutically acceptable salts or tautomers thereof which are inhibitors of poly(ADP-ribose)polymerase (PARP) and thus useful for the treatment of cancer, inflammatory diseases, reperfusion injuries, ischaemic conditions, stroke, renal failure, cardiovascular diseases, vascular diseases other than cardiovascular diseases, diabetes mellitus, neurodegenerative diseases, retroviral infections, retinal-damage, skin senescence and UV-induced skin damage, and as chemo-or radiosensitizers for cancer treatment and are also useful for reducing cell necrosis (in stroke and myocardial infarction), down regulating inflammation and tissue injury, treating retroviral infections and protecting against the toxicity of chemotherapy.
