GlaxoSmithKline (GSK) is rumoured to have approached a number of private equity firms to gauge the interest for a range of its older drugs as it attempts to refresh its portfolio.According to various reports, the pharmaceutical group has contacted companies including Advent International, Blackstone and KKR regarding a £7.5bn portfolio of mature products.The speculation follows comments made by Chief Executive Sir Andrew Witty in GSK's first-quarter results last month, who said that the firm "continue[s] to evaluate options to maximise the value of our portfolio and are currently reviewing our Established Products Portfolio (EPP)".The portfolio, comprised of drugs which have lost patent protection, is said to include the antidepressant drug Paxil, migraine treatment Imitrex and stomach acid remedy Zantac.The EPP contributed £814m of £5.61bn revenue generated in GSK's first quarter, but sales from the portfolio were down 11% year-on-year.Any potential transaction with private-equity firms is likely to be a sale of individual medicines or a group of products, rather than the disposal of the whole portfolio.BC