OBJECTIVES: To assess covariates that affect the duration of pain relief doxepin oral rinse provided cancer patients with painful oral mucositis. METHODS: Fifty consecutive patients with oral mucositis due to head and neck radiation therapy participated in the original study. An examination of the mouth was completed and oral mucositis scored using the Oral Mucositis Assessment Scale (OMAS) which assesses erythema severity and ulceration size. Oral pain was assessed with a visual analogue scale (VAS) prior to taking the rinse and then at five, 15, 30 minutes, one-hour, while continuing every half hour up to three-hours, and at four-hours following rinsing. The time until recurrence of pretest pain level was defined as the time it took for VAS pain scores to reach or exceed initial pain scores. Recurrence of pain relief was right censored at four-hours for twenty patients; survival analysis was utilized to determine what factors were associated with recurrence of pain. RESULTS: Significant pain reduction was reported. Patients described, on average, a 55.6% reduction in pain after 15 minutes of doxepin rinsing. Recurrence of pain was slow and significant reduction in pain from baseline continued at four hours (p<0.0001). The hazard ratios from the Cox proportional hazards model (p<0.001) determined that holding all other variables constant, an increase by one unit in either the baseline pain severity, the worst documented erythema score, or the relative reduction of pain at 15 minutes, decreased the rate of pain recurrence at any time (t) by 45.3, 38.8, or 71.8% respectively. CONCLUSIONS: This research shows good results for doxepin oral rinse. Mucositis patients who reported higher baseline pain, more severe erythema, or larger relative reductions in pain after 15 minutes of rinsing, had a larger probability of extended pain relief.