Despite a healthy rise in revenues, signs that AbbVie's big-selling Humira drug may be showing its age led to a decline in its share price late last week.
The company reported fourth-quarter revenues of $6.3bn - up more than 18% - with Humira (adalimumab) rising 13% to $3.8bn which did not meet some analysts' expectations.
The world's biggest-selling drug consolidated its position at the top of the tree with total annual sales of over $14bn - roughly in line with the company's forecasts - although an ex-US growth rate of less than 10% raised further eyebrows.
Meanwhile, management suggestions that the drug's growth outside the US could continue to slow during 2015 thanks to indirect competition from biosimilar's of a Humira rival - Enbrel - added to investor anxieties.
However, the company's chief executive officer Rick Gonzalez insisted however that growth in the US is robust and there is no sign of a slowdown.
Aside from biosimilars, Humira could also face increasing competition from new molecular entities (NMEs) due to reach the market in the coming months, including Lilly and Incyte's baricitinib, which could be available for prescribing later this year. In trials, baricitinib outperformed Humira on some outcome measures in rheumatoid arthritis patients.
With 60% of its revenues coming from Humira, AbbVie needs new drugs such as hepatitis C virus therapy Viekira Pak (ombitasvir/paritaprevir/ritonavir and dasabuvir) and cancer therapy Imbruvica (ibrutinib) to grow quickly as it prepares for the loss of patent protection for Humira in the coming years.
There was mixed news for the company on these products. Imbruvica grew 48% in the further quarter to reach $343m, while recently launched Viekira Pak brought in $554m, up from $469m in the third quarter.
While top-line performance seemed strong for both drugs, AbbVie has scaled back its 2016 sales forecast for Viekira Pak from $3bn to $2bn, in part because of the imminent launch of Merck & Co's cut-price rival Zepatier (elbasvir/grazoprevir) and also because its label was updated recently to include a recommendation for physicians to assess liver function prior to treatment and during treatment in cirrhotic patients.
Imbruvica broke into the blockbuster category for the first time in 2015 with annual sales of more than $1bn, but is also facing competition from the likes of AstraZeneca (AZ) and Acerta's acalabrutinib which is in late-stage development.
Shares in AbbVie closed down a little over 2% on Friday.