The goal of this clinical trial is to explore the effectiveness and adverse reactions of doxepin solution spray for alleviation of stubborn breakthrough pain induced by swallowing in patients receiving radiotherapy for nasopharyngeal carcinoma.

Patients with nasopharyngeal carcinoma receiving radical radiotherapy or chemoradiotherapy who developed oral mucositis and had a swallowing-induced pain score ≥ 4 were recruited and randomly assigned 1:1 to the experimental group and the control group.

Patients in the experimental group received a doxepin solution spray to the posterior pharyngeal wall 10 minutes before eating. At least 12 hours later, when the swallowing-induced pain score ≥4, a placebo spray was administered to the posterior pharyngeal wall 10 minutes before eating.

Patients in the control group received a placebo spray to the posterior pharyngeal wall 10 minutes before eating. At least 12 hours later, when the swallowing-induced pain score ≥4, a doxepin solution spray was administered to the posterior pharyngeal wall 10 minutes before eating.

The swallowing-induced pain and incidence of adverse events were assessed at 10 minutes, 20 minutes, 30 minutes, and 1 hour after medication using a patient-reported questionnaire, and safety evaluation was conducted 1 day after treatment.

Inclusion Criteria:

1. Provide informed written consent.
2. Age ≥ 18 years.
3. Histologically confirmed as nasopharyngeal carcinoma, and currently undergoing radical radiotherapy or chemoradiotherapy.
4. Physical examination demonstrating the presence of radiation-induced mucositis in the oral cavity and/or oropharynx.
5. At least 4 (out of 10) patient-reported swallowing-induced pain as measured by the numeric rating scale of pain.
6. Being able to complete the questionnaires independently or with assistance.
7. ECOG Performance Status 0, 1 or 2.

Exclusion Criteria:

1. Known allergy to doxepin, tricyclic antidepressants, or any known component of the drug formulation.
2. Use of a tricyclic antidepressant or monoamine oxidase inhibitor within 14 days prior to registration.
3. Current untreated or unhealed oral candidiasis or oral herpes simplex virus infection.
4. Untreated narrow angle glaucoma within 6 weeks prior to registration.
5. Untreated urinary retention within 6 weeks prior to registration.
6. Administration of cryotherapy to prevent oral mucositis within 6 weeks prior to registration.
7. Current serious heart disease or a recent history of myocardial infarction.
8. Current untreated or unresolved conditions like epilepsy, hyperthyroidism, hepatic dysfunction, delirium, and neutropenia.
9. Pregnant or lactating women.