This CPB has been revised to: (i) include arginase deficiency as a medically necessary indication for sodium phenylbutyrate (Buphenyl) therapy when criteria met, and (ii) require elevated plasma ammonia levels at baseline for chronic management of urea cycle disorder, including arginase deficiency. This CPB has been updated with the following: (i) created subheaders, (ii) reorganized the policy format, and (iii) added additional dosage and administration.