What toxicity is of most concern with the first dose of rituximab?

• A. Neuropathy
• B. Hypersensitivity reaction
• C. Cardiac arrhythmia
• D. Hemorrhagic cystitis

Answer: (B)

The main idea is that the most concerning toxicity with the first dose of rituximab is an infusion-related hypersensitivity reaction caused by rapid cytokine release when B cells are targeted.

This reaction happens as the monoclonal antibody binds CD20 on B cells, leading to their rapid activation and destruction, which releases cytokines. Clinically, it can present with fever, chills, rigors, flushing, hypotension, wheezing, and sometimes bronchospasm or hypoxia. Because it can escalate quickly, it’s the primary safety focus at the start of therapy, and it’s why patients are premedicated and monitored closely during the initial infusion.

Other listed toxicities aren’t typically the immediate first-dose concern. Neuropathy is a possible but less acutely presenting adverse effect and not the hallmark of the initial infusion. Cardiac arrhythmias and hemorrhagic cystitis are not characteristic first-dose risks with rituximab.