Global biopharmaceutical company AbbVie (NYSE:ABBV) reported its fourth-quarter earnings results before the opening bell this morning and pointed to an increasingly difficult environment due to generic competition.

For the quarter, AbbVie delivered worldwide revenue of $5.11 billion, representing a 1.8% decline that includes a negative 0.7% effect for currency translation. Profit for the quarter shrank to a diluted $0.70 per share from $0.98 in the year-ago period as operating profits were negatively affected in the U.S. by the introduction of generic drugs.

The most important pipeline product to AbbVie is Humira, which contributed 59.5% of AbbVie's $5.11 billion in sales this quarter, and finished the year as the best-selling drug in the world with $10.66 billion in revenue. International sales of Humira rose by 8.2% while revenue in the U.S. pushed higher by 18.1%. Total Humira sales increased 13.4% for the quarter.

Within the remainder of AbbVie's product line, Synagis, AndroGel, Kaletra, and Lupron -- which delivered between $209 million and $314 million in revenue for the quarter -- all saw reported sales decline, with AndroGel's 20.9% decline being the steepest.

Looking toward 2014, AbbVie forecasts revenue of approximately $19 billion, which doesn't include any positive impact from the potential approval and launch of its hepatitis C direct-acting antiviral combo drug, and projects earnings per share to range between $3 and $3.10 on an adjusted basis.