Participants will receive a single oral dose of diphenhydramine 50 mg administered 30-60 minutes before the scheduled standard-of-care anti-CD20 infusion at each visit.

Fatigue severity will be assessed using the Visual Analogue Scale to Evaluate Fatigue Severity (VAS-F), a validated 18-item self-administered instrument that measures the participant's current experience of fatigue and energy. Each item is scored by marking a point along a 100-mm visual analogue line anchored by "Not at all tired" (0 mm) and "Extremely tired" (100 mm). Scores are recorded as the distance in millimeters from the left anchor, producing a score range of 0-100 mm, with higher scores indicating greater fatigue severity.

Total duration, in minutes, that the participant occupies the infusion chair during each study visit. Chair time will be measured from the participant's arrival for the infusion appointment to the time of discharge.

Incidence of treatment-related toxicity will be reported as the number of participants experiencing treatment-related adverse events (AEs). AEs will be assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) version 5.0, per physician discretion and will be identified through retrospective review of infusion documentation and follow-up assessments.

Incidence of treatment-related toxicity will be reported as the number of participants experiencing treatment-related serious adverse events (SAEs). SAEs will be assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) version 5.0, per physician discretion and will be identified through retrospective review of infusion documentation and follow-up assessments.