Pfizer reported a large drop in fourth-quarter earnings due to higher expenses and the strong dollar, but said it was on track to complete its takeover of Allergan.

Earnings for the quarter ending December 31 were $613 million, a 50 percent drop compared with the year-ago period.

Revenues rose 7.1 percent to $14 billion.

They were boosted by a 53 percent gain in global vaccines revenues and a 61 percent rise in global oncology. The results also included about $1.1 billion in sales from Pfizer's acquisition of Hospira, which specializes in injectable drugs.

However, revenues were negatively hit by $934 due the strong dollar. The company also notched large increases in selling, informational and administrative expenses, which includes marketing. Research and development expenses also jumped from clinical trials on oncology and other pipeline drugs.

Pfizer chief executive Ian Read said he expects the Allergan deal to close in the second half of 2016.

"We see this transaction as a very effective driver of accelerating the growth potential of our Innovative business, strengthening our Established business and more efficiently allocating our capital globally," Read said.

For all of 2015, Pfizer reported earnings of $7.7 billion, down 15.2 percent from 2014. Revenues dipped 1.5 percent to $48.9 billion.

Pfizer projects 2016 adjusted net income of $2.20-$2.30 per share.

It forecast 2016 revenues of $49-$51 billion, with an expected $2.3 billion hit from lost exclusivity on drugs to generic competition and another $2.3 billion drag from the strong dollar.

The forecast was below analyst expectations for earnings of $2.36 per share and revenues of $52.5 billion.

Pfizer shares fell 1.1 percent to $29.85 in pre-market trade.