The present invention relates to novel substituted 2-(5-hydroxy-2-methyl-1H-indol-3-yl)acetic acids, to novel antiviral active ingredients, pharmaceutical compositions, antiviral medicaments, methods for prophylaxis and treatment of viral diseases particularly caused by influenza viruses and infectious hepatisis C (HCV) viruses.Novel substituted 2-(5-hydroxy-2-methyl-1H-indol-3-yl)acetic acids, their esters of the general formula 1 and pharmaceutically acceptable salts and/or hydrates thereof have been disclosed wherein: R1 represents amino group substituent selected from hydrogen, optionally substituted C1-C5 alkyl, acyl or sulfonyl; R2 and R4 independently of each other represent alkyl substituent selected from hydrogen, halogen, optionally substituted C1-C3 alkyl, optionally substituted hydroxyl, optionally substituted amino group, optionally substituted aminomethyl, substituted mercapto group; R3 represents hydrogen, optionally substituted lower C1-C5 alkyl; R5 represents cyclic system substituent selected from hydrogen, fluorine, trifluoromethyl, carboxy group, alkyloxycarbonyl, possibly substituted aryl, heterocyclyl, optionally substituted aminomethyl, cyano group; R6 represents hydroxyl group substituent selected from hydrogen, optionally substituted C1-C5 alkyl, acyl.