Wesfarmers’ proposed takeover bid of Priceline Pharmacy owner Australian Pharmaceutical Industries is under fire, after Sigma Healthcare put forward a new merger deal, which API’s board has acknowledged as a superior offer.

Sigma has offered a mix of cash and Sigma Healthcare stock, which values API as $774 million – over 1 per cent more than the Wesfarmers offer, which is wholly cash-based, and still under due diligence.

While this throws a spanner in the works for Wesfarmers, both deals are subject to the due diligence investigations, regulatory approvals, and need the “unanimous recommendation” of the API board.

In addition, major share holder Washington H. Soul Pattinson, which controls 19.3 per cent of API shares, has committed to voting in favour of the Wesfarmers deal.