Fifty-four lawsuits, mostly involving suicides and attempted suicides by teenagers in various parts of the country, accuse the New York-based pharmaceutical company of concealing a negative pediatric study on Celexa, duping physicians about the drug’s clinical trials, and targeting children in aggressive promotions of Celexa and a sister drug, Lexapro. Four of the cases were settled Friday, and two additional cases were settled in recent weeks. A surge of related settlements, which could total millions of dollars, is expected in the months ahead as the pharmaceutical company attempts to move beyond the controversy surrounding its marketing of antidepressants to children.