At least three private equity firms are planning to bid for a clutch of GlaxoSmithKline’s (GSK.L) non-prescription products, expecting limited competition from rival large pharma groups, people familiar with the process said. Advent International, Cinven CINV.UL and Warburg Pincus WP.UL are among firms considering bids for the over-the-counter (OTC) products, which include painkillers and vitamin supplements, people said. GSK, Britain’s biggest drugmaker, said in February it planned to sell several non-core products with combined sales of around 500 million pounds ($817 million), representing about 10 percent of its total consumer healthcare business.