A Clinical Study to Compare BupiZenge With Lidocaine for Pain Due to Oral Mucositis in Patients With Head and Neck Cancer.

Inclusion Criteria: * Participant must provide signed written informed consent prior to trial participation and must be willing and able to comply with all requirements and restrictions of the trial. * Male or female aged ≥ 18 on the day of consent and ≤ 80 on the first day of dosing. * Pathologically confirmed diagnosis of squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx, or nasopharynx. * About to start IMRT with curative intent with daily fractions of 2.0 Gy to 2.2 Gy to a cumulative intended dose of at least 60 Gy and a maximum of 72 Gy. Proton therapy given at equivalent biological doses is allowed. * Eastern Cooperative Oncology Group (ECOG) Performance Status 0-2. * Female participants of childbearing potential (WOCBP) must agree to use a highly effective contraceptive measure or practice total sexual abstinence from the time of giving informed consent until at least 24 hours after last dose of IMP. Exclusion Criteria: * Participation in another investigational interventional clinical trial within 3 months prior to first dosing, or for a longer period if required by local regulations, or within 5 half-lives of the investigational agent taken (whichever is longer). An exception is studies where patients are randomized to different radiotherapy settings, e.g. participation in DAHANCA 35 is allowed. * Previous radiation therapy to the head and/or neck area. * Pre-existing OM, active herpes simplex virus (HSV) infection, or untreated or uncontrolled oral candidiasis. * Receiving high-dose (\> 15 mg per day prednisolone), corticosteroids (for any indication). * Known allergy or intolerance to bupivacaine, lidocaine, or any of the excipients in the products. * Significant cardiac disease such as AV block II-III or requiring treatment with antiarrhythmic drugs in class III (e.g., amiodarone). * Inability to eat or drink, or dependence on an enteral feeding tube (percutaneous endoscopic gastrostomy \[PEG\] or nasogastric tube) for any reason. * Moderate/severe liver or kidney disease defined as: 1. AST/ALT \> 3 × upper limit of normal (ULN) or bilirubin \> 1.5 × ULN (unless related to Gilbert's syndrome) 2. glomerular filtration rate (GFR) \< 30 mL/min/1.73 m2 * Known diagnosis of epilepsy. * Known phenylketonuria (PKU). * Pregnancy or breastfeeding. * Any condition or circumstance-based on the investigator's assessment-that could increase risk to the participant, confound trial results, or interfere with compliance / participation (including inability or unwillingness to follow trial procedures, or any clinically significant physical or psychiatric condition).