Pfizer is spending around $4.2 billion on the purchase of Anacor Pharmaceuticals, thus securing access to the firm's flagship non-steroidal topical PDE4 inhibitor crisaborole.

Crisaborole is currently being reviewed by US regulators as a potential treatment for mild-to-moderate atopic dermatitis (eczema), with a decision expected in by January 7 next year 2017.

According to Pfizer, the drug could achieve or exceed peak sales of more than $2 billion a year if it makes it to market, given its performance in Phase III trials and sizeable target market; up to 25 million people in the US are thought to suffer from the condition.

"We believe the acquisition of Anacor represents an attractive opportunity to address a significant unmet medical need for a large patient population with mild-to-moderate atopic dermatitis, which currently has few safe topical treatments available," noted Albert Bourla, Group President of Pfizer's Global Innovative Pharma and Global Vaccines, Oncology and Consumer Healthcare Businesses.

"We believe we are well positioned to maximize crisaborole's commercial potential through our strong relationships with paediatricians and primary care physicians," he said, further explaining Pfizer's strategy behind the move.

Anacor also holds the rights to Kerydin, a topical treatment for onychomycosis (toenail fungus) that is distributed and commercialised by Sandoz in the US.

Under the terms of the merger agreement, which has been agreed by both sets of directors a subsidiary of Pfizer will start a cash tender offer to purchase all of the outstanding shares of Anacor common stock for $99.25 per share.

Pfizer said it expects to complete the acquisition in the third-quarter 2016.

The move comes just days after drug giant signed a $900 million metabolic diseases pact with Wave Life Sciences, and reports that it is one of a few pharmas currently circling US biotech Medivation, in the aftermath of its failed $160-billion deal with Allergan.