Fuad El-Hibri plans to retire as chief executive of Rockville-based Emergent Biosolutions effective April 1, 2012, the company announced today, after serving as head of the biotechnology firm since its formation in 1998.

Emergent’s current president and chief operating officer, Daniel J. Abdun-Nabi, has been chosen as his successor. El-Hibri will remain with the company as executive chairman and shift his attention exclusively to corporate strategy and merger and acquistion opportunities.

The departure comes as Emergent expands its product portfolio beyond BioThrax, the only anthrax vaccine licensed by the U.S. Food and Drug Administration. It’s products under development include treatments for typhoid, tuberculosis, rheumatoid arthritis and chronic lymphocytic leukemia.

As Capital Business reporter Marjorie Censer wrote in January, Emergent got its start when El-Hibri paid $25 million in cash and commitments at an auction in 1998 for a government facility in Lansing, Mich. that produced an anthrax vaccine.

The company posted $1.5 million in net income for the third quarter of 2011 on total revenue for the three-month period of $58.8 million.