Background: The De-ESCALaTE trial confirmed the superiority of cisplatin over cetuximab in combination with radiotherapy for the treatment of low risk human papillomavirus positive oropharyngeal cancer (HPV+OPC). The most common serious adverse events (SAEs) for cisplatin were due to vomiting and nausea, in contrast with oral mucositis and vomiting for concurrent cetuximab. In this study, we examined the efficacy of different hydration and anti-emetic policies in preventing cisplatin-related gastrointestinal and renal toxicities as well as related SAEs in the cisplatin arm of the De-ESCALaTE trial. Methods: This was a post-hoc pre-specified analysis of data collected within the De-ESCALaTE trial including pre-hydration, diuretics, the amount of intravenous (IV) fluids before, during and after chemotherapy, whether oral fluid hydration was advised and type of antiemetic regimen prescribed, if any, after chemotherapy administration, including if a triple antiemetic regimen with a NK1 receptor antagonist, steroids and a serotonin 5-HT3 antagonist was given before and after chemotherapy. The primary outcome was number of SAEs per patient; secondary outcome was number per patient of cisplatin-induced severe toxicity events of interest: nausea, vomiting, dehydration or renal toxicity. Results: 166 (mean age 57 yrs; 132 m, 34 f) patients received cisplatin. Hydration and anti-emetics policies for cisplatin treatment are significantly correlated with the rate of SAEs and acute severe nausea, vomiting, dehydration or renal toxicities. Using stepwise backwards multivariable ordinal logistic regression in the presence of baseline characteristics, use of a triple anti-emetics regimen (OR 0.41,p = 0.032) and 2.5 to 3L IV fluids given before and during cisplatin chemotherapy (OR 0.161, p = 0.009) as well as oral fluids advised post chemotherapy (OR 0.365, p = 0.03) were associated with a significantly lower incidence of SAEs and severe toxicities of interest. We will also present data on relative cost-effectiveness of the different regimens. Conclusions: Based on our results, we recommend the use of a triple anti-emetic regimen, adequate hydration of 2.5-3L before and during chemotherapy as well as advising patients to take oral fluids advised to reduce cisplatin toxicities related to nausea, vomiting, dehydration and/or renal injury. Clinical trial information: ISRCTN33522080.