A compound, or a tautomer thereof, or a pharmaceutically acceptable salt or ester thereof, for use in the treatment of pulmonary fibrosis in a subject, wherein the compound is of the formula: wherein X is SO 2; b is zero; a and c are each independently 0, 1, 2, 3, 4 or 5; R 1 and R 3 are each independently selected from C 1 -C 6 alkyl, substituted C 1 -C 6 alkyl, halogen, C 1 -C 8 alkoxy and substituted C 1 -C 8 alkoxy; A is an amidino-containing moiety having the structure of: wherein R 4 is H; R 5 is C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, -NH 2, -N(C 1 -C 6 alkyl) 2, -NH(C 1 -C 6 alkyl), phenyl, a monocyclic or bicyclic heteroaryl that includes at least one nitrogen heteroatom, or a monocyclic or bicyclic heterocycloalkyl that includes at least one nitrogen heteroatom; or R 5 is C 1 -C 6 alkyl, -N(C 1 -C 6 alkyl) 2, -NH(C 1 -C 6 alkyl), or -NHC CH 3; or R 5 is an amino of the formula -NR 30 R 31, where R 30 and R 31 are, independently, hydrogen or an optionally-substituted C 1 -C 6 alkyl, provided that at least one of R 30 and R 31 is optionally substituted C 1 -C 6 alkyl; or R 5 is a thiol substituted with a C 1 -C 6 alkyl or a substituted C 1 -C 6 alkyl; wherein substituted C 1 -C 6 alkyl is a C 1 -C 6 alkyl wherein one of more hydrogen atoms are substituted with halogen, cycloalkyl, C 1 -C 8 alkoxy, -NH 2, hydroxyl, aryl, alkenyl with up to 6 carbon atoms or carboxyl; and substituted C 1 -C 8 alkoxy is C 1 -C 8 alkoxy substituted with alkenyl with up to 6 carbon atoms, alkynyl with up to 6 carbon atoms, aryl, aryl-C 1 -C 6 alkyl, cycloalkyl, halogenated C 1 -C 6 alkyl, or C 1 -C 8 alkoxy. X is SO 2; b is zero; a and c are each independently 0, 1, 2, 3, 4 or 5; R 1 and R 3 are each independently selected from C 1 -C 6 alkyl, substituted C 1 -C 6 alkyl, halogen, C 1 -C 8 alkoxy and substituted C 1 -C 8 alkoxy; A is an amidino-containing moiety having the structure of: wherein R 4 is H; R 5 is C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, -NH 2, -N(C 1 -C 6 alkyl) 2, -NH(C 1 -C 6 alkyl), phenyl, a monocyclic or bicyclic heteroaryl that includes at least one nitrogen heteroatom, or a monocyclic or bicyclic heterocycloalkyl that includes at least one nitrogen heteroatom; or R 5 is C 1 -C 6 alkyl, -N(C 1 -C 6 alkyl) 2, -NH(C 1 -C 6 alkyl), or -NHC CH 3; or R 5 is an amino of the formula -NR 30 R 31, where R 30 and R 31 are, independently, hydrogen or an optionally-substituted C 1 -C 6 alkyl, provided that at least one of R 30 and R 31 is optionally substituted C 1 -C 6 alkyl; or R 5 is a thiol substituted with a C 1 -C 6 alkyl or a substituted C 1 -C 6 alkyl; wherein substituted C 1 -C 6 alkyl is a C 1 -C 6 alkyl wherein one of more hydrogen atoms are substituted with halogen, cycloalkyl, C 1 -C 8 alkoxy, -NH 2, hydroxyl, aryl, alkenyl with up to 6 carbon atoms or carboxyl; and substituted C 1 -C 8 alkoxy is C 1 -C 8 alkoxy substituted with alkenyl with up to 6 carbon atoms, alkynyl with up to 6 carbon atoms, aryl, aryl-C 1 -C 6 alkyl, cycloalkyl, halogenated C 1 -C 6 alkyl, or C 1 -C 8 alkoxy. R 4 is H; R 5 is C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, -NH 2, -N(C 1 -C 6 alkyl) 2, -NH(C 1 -C 6 alkyl), phenyl, a monocyclic or bicyclic heteroaryl that includes at least one nitrogen heteroatom, or a monocyclic or bicyclic heterocycloalkyl that includes at least one nitrogen heteroatom; or R 5 is C 1 -C 6 alkyl, -N(C 1 -C 6 alkyl) 2, -NH(C 1 -C 6 alkyl), or -NHC CH 3; or R 5 is an amino of the formula -NR 30 R 31, where R 30 and R 31 are, independently, hydrogen or an optionally-substituted C 1 -C 6 alkyl, provided that at least one of R 30 and R 31 is optionally substituted C 1 -C 6 alkyl; or R 5 is a thiol substituted with a C 1 -C 6 alkyl or a substituted C 1 -C 6 alkyl; wherein substituted C 1 -C 6 alkyl is a C 1 -C 6 alkyl wherein one of more hydrogen atoms are substituted with halogen, cycloalkyl, C 1 -C 8 alkoxy, -NH 2, hydroxyl, aryl, alkenyl with up to 6 carbon atoms or carboxyl; and substituted C 1 -C 8 alkoxy is C 1 -C 8 alkoxy substituted with alkenyl with up to 6 carbon atoms, alkynyl with up to 6 carbon atoms, aryl, aryl-C 1 -C 6 alkyl, cycloalkyl, halogenated C 1 -C 6 alkyl, or C 1 -C 8 alkoxy.