XDH and hepatitis A virus infection: As for PZA-induced hepatitis, recently PZA metabolites pyrazinoic acid and 5-hydroxypyrazinoic acid have been reported to correlate with PZA-induced hepatitis.34 The conversion of PZA to pyrazinoic acid, and that of 5-hydroxy-PZA to 5-hydroxypyrazinoic acid both involve an amidase (Supplementary Figure S4, http://links.lww.com/MD/A303).35 The other source of 5-hydroxypyrazinoic acid production is from pyrazinoic acid via xanthine oxidase.