SmithKline Beecham PLC, the newly merged health, household products and pharmaceuticals company, said Wednesday its first quarter profit jumped 42 percent because of the sale of certain businesses. SmithKline said that during the three months ended March 31 it netted $371 million, or 18 cents a share, compared with earnings of $261 million, or 20 cents, a year ago. Sales rose 19 percent to $2.15 billion from $1.8 billion. The results were the first the company reported on a quarterly basis since the merger of SmithKline Beckman Corp. and Beecham PLC in July 1989. Year-earlier figures were made available as if the merger had taken place at the beginning of 1989. SmithKline Beecham attributed the higher quarterly income largely to aset sales. It sold branded businesses such as Ambrosia, Bovril and Marmite food products as well as the Yardley-Lentheric cosmetics, raising around $493 million. The company said that it reduced its debt by $455 million during the first quarter. Its total debt stands at $2.5 billion, down from $4 billion a year ago. SmithKline Beecham Chairman Henry Wendt said that ``interest expense will decline significantly during the year, and the balance sheet will improve as we generate a high level of cash from operations and aggressively pursue debt reduction.'' The pound figures were converted at a rate of $1.65, which was provided by the company.