TURNOVER at Glaxo Wellcome, the world's largest pharmaceuticals company, increased 5% in the first half of the year despite a 16% drop in sales of its best selling anti ulcer drug Zantac. The company today reported pre tax profits of £1.55 billion for the half year, up from £1.16 billion in the first six months of 1995 when Wellcome was only included for three months after the merger with Glaxo.