The firm announced it had agreed a deal with the board of California-based Anacor Pharmaceuticals.
Anacor's flagship product is crisaborole, a cream for eczema which is awaiting approval by US regulators.
The deal comes just weeks after Pfizer scrapped a planned $160bn merger with Irish drugmaker Allergan for tax reasons.
"We believe the acquisition of Anacor represents an attractive opportunity to address a significant unmet medical need for a large patient population," said Albert Bourla, head of Pfizer's global innovative pharma unit.
Crisaborole can achieve $2bn (£1.4bn) in annual sales if approved by the US Food and Drug Administration, according to Pfizer.
Some 18 million to 25 million people suffer from eczema in the US, but currently there are few safe appropriate treatments, Pfizer said.
Anacor shares jumped 57%, rising above the $99.25 a share agreed with Pfizer.

Chapelcross, near Annan, is one of five sites being considered but is the only one north of the border.
Capenhurst in Cheshire, Sellafield in west Cumbria and Aldermaston and Burghfield, both in Berkshire, are the other possible locations.
The consultation was at the Victoria Halls in Annan on Friday.
Councillor Ronnie Ogilvie, who chairs the Chapelcross Site Stakeholders Group, said it was important as many people as possible took the opportunity to examine the proposals and express their opinion.
The UK government has pledged that public opinion will be taken into account in deciding the final location.
Consultation will run until February around all the locations on the shortlist.
Ministers are planning that waste from nuclear-powered Royal Navy submarines which have left service would be stored at one of the sites until "some time after 2040" when the UK's deep level underground waste dump is available.
US drugs giant Pfizer will acquire the maker of a new eczema treatment in a deal worth $5.2bn (£3.6bn).
[NEXT_CONCEPT]
A final consultation event has been held on proposals to use a former Scots nuclear plant to store radioactive waste from redundant submarines.