Vivus Inc., a Mountain View drug maker with several promising treatments in the pipeline, has just signed for a big new headquarters space in the city. Vivus is taking 45,240 square feet at 351 East Evelyn Ave. in Mountain View. The company signed an 84-month lease with landlord SFERS Real Estate Corp. U, which appears to be a subsidiary of RREEF Real Estate, according to California incorporation documents. It’s a big size increase from Vivus’ current digs. According to SEC filings, Vivus was in about 18,000 square feet at the Castro Commons office building, at 1172 Castro St. In the new space, Vivus will pay a starting annual rent of $31.20 per square foot and will occupy the space beginning in the spring of 2013.