(Reuters) - AbbVie Inc on Friday posted a fourth-quarter profit that missed Wall Street estimates, as the drugmaker's top-selling drug, Humira, faces competition from cheaper rival versions in Europe.

Rheumatoid arthritis drug Humira is the world's best-selling prescription medicine and in the six years since AbbVie spun out from device maker Abbott Labs, the drug has remained by far its top-earner, accounting for about 60 percent of net revenue.

AbbVie in November lowered its forecast for overseas sales of Humira, citing stiff competition in Europe from drugmakers including Mylan NV and Biogen Inc. In the United States, Humira is not expected to face biosimilar competition until 2023.

The company said international sales of Humira fell 17.5 percent on a reported basis to $1.30 billion (992.90 million pounds), on the back of "direct biosimilar competition in certain international markets."

In the fourth quarter, Humira brought in sales of $4.92 billion, falling short of the $5.02 billion forecast by six analysts polled by Refinitiv IBES.

Cancer drug Imbruvica, which AbbVie has earmarked as key to its plan to rely less on Humira in future, brought in sales of $1.01 billion, in line with analysts' estimates.

The company has previously talked up its cancer drug portfolio, which it says will buoy revenue as sales of Humira decline in future, but a recent trial setback for Imbruvica and the failure of its expensive cancer drug Rova-T have worried investors.

The drugmaker said it expects 2019 adjusted earnings of between $8.65 and $8.75 per share, largely below the average analyst forecast of $8.74 per share.

AbbVie posted a loss of $1.83 billion, or $1.23 per share, for the quarter ended Dec. 31, compared with a profit of $52 million, or 3 cents per share, last year, when it took a tax-related charge.

In the latest quarter, the drugmaker recorded $4.12 billion in impairment charges related to the scrapping of its development program for Rova-T, which AbbVie acquired as part of its $5.8 billion purchase of Stemcentrx in 2016.

Excluding items, AbbVie earned $1.90 per share, falling short of the Wall Street target of $1.94 per share.

Net revenue rose 7.3 percent to $8.31 billion in the quarter, but came below the average analyst estimate of $8.38 billion.

(Reporting by Tamara Mathias in Bengaluru; Editing by Maju Samuel)