Severe and sometimes fatal infusion reactions may occur with rituximab. These reactions may occur while you receive rituximab or within 24 hours after you receive it. Tell your doctor right away if you develop blurred vision, chest pain, cough, dizziness, drowsiness, fainting, fast or irregular heartbeat, headache, hives, itching, numbness of an arm or leg, shortness of breath, swelling (eg, lips, tongue, throat, face), trouble breathing, weakness, or wheezing while you receive or after you receive rituximab. Severe and sometimes fatal skin and mouth reactions (Stevens-Johnson syndrome/toxic epidermal necrolysis) may occur during treatment with rituximab. Tell your doctor right away if you experience red, swollen, peeling, or blistered skin; or sores or ulcers on your skin, lips, or in your mouth. If you have had hepatitis B before or carry the virus, rituximab can cause the virus to become active again. This can lead to severe and sometimes deadly liver problems. Your...