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The clinical arm is twelve patients without an established organic cause, so it establishes the target rather than the treatment effect.\nexposure: Sildenafil assayed against phosphodiesterase isozymes prepared from human tissue\nevidence_span: {\"source_cache\": \"artifacts/sildenafil-research/8858389.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"173f69debd8427b8a1c001e543e4356f2d3b90c730ca3217073a25c4bc61905a\", \"start_char\": 0, \"end_char\": 1288, \"text_sha256\": \"173f69debd8427b8a1c001e543e4356f2d3b90c730ca3217073a25c4bc61905a\"}\n[sil-p8858389] Sildenafil: an orally active type 5 cyclic GMP-specific phosphodiesterase inhibitor for the treatment of penile erectile dysfunction. 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