The drug, which currently has US Food and Drug Administration approval to treat non-Hodgkin’s lymphoma, is undergoing clinical trials for rheumatoid arthritis.
Genentech senior manager of product comms Megan Pace said it was the first time the company had worked with Weber Shandwick.
The agency won the account through a competitive tender. Pace declined to discuss the other firms that were considered.
Results from Phase IIa clinical trials of the drug were recently published in the New England Journal of Medicine.
According to Genentech, there are over 150 trials under way with more than 10,000 patients, studying the safety and efficacy of Rituxan in a number of malignant and non-malignant conditions.
Rituxan, which is the second highest-selling drug in the US, was approved for the European Union in 1998 under the trade name MabThera.