A 45-year-old male with chronic schistosomiasis for 10 years presents with hepatomegaly (liver 1.5 cm below costal margin, 4 finger-breadths below xiphoid), splenomegaly reaching umbilical level, positive serum anti-Schistosoma japonicum antibody, and elevated ALT (100 U/L) without jaundice. The most effective treatment for the pathogen is: