RESUMEN
A 64-year-old female received modified FOLFOX6 therapy with continuous administration of a high concentration of 5-fluorouracil (5-FU) for recurrence of peritoneal dissemination after total gastrectomy. Twenty-nine hours after the administration, there was the sudden onset of altered consciousness and hepatic dysfunction accompanied by hyperammonemia. The consciousness and hepatic function improved the following day after treatment with branched-chain amino acid formulation, lactulose, fresh frozen plasma, and continuous hemodiafiltration. Thus, the diagnosis was 5-FU-induced hyperammonemia. Improvement of dehydration and renal dysfunction would be important for avoiding the risk of developing the side effects. Because recurrent gastric cancer is often a progressive condition, post-treatment might be promptly transferred to the other posterior regimen without 5-FU as required.