Drug major AstraZeneca has said its 2006 profit will come in at the low end of its forecasts after a generic version of its third best-selling blood pressure drug Toprol XL reached the US market a little earlier than expected.

The onset of generic competition to the product, kicked off by Novartis’ generic subsidiary Sandoz, had been on the cards since AstraZeneca lost a lawsuit to defend a key patent for Toprol XL (metoprolol succinate) in January.

AstraZeneca has taken the defensive measure of cutting a deal with Par Pharmaceuticals to launch an ‘authorised’ generic version of the product, but is still likely to see a significant decline in Toprol XL sales over the coming months.

Last year, sales of the drug (sold as Seloken in some markets) grew 24% to $1.74 billion, with a massive $1.3 billion of that total coming from the USA.

In a statement, AstraZeneca said it expected 2006 earnings per share (EPS) to be at the lower end of its $3.85 to $3.95 forecast range.

Although Toprol XL competition has arrived more or less as predicted, AstraZeneca is under pressure at the moment with three of its top products – Nexium (esomeprazole), Seroquel (quetiapine) and Symbicort (formoterol and budesonide) – facing patent challenges in the courts, and a number of late-stage disappointments leaving its pipeline looking thin.

Analyst Navid Malik at Collins Stewart said the market is now focusing heavily on AstraZeneca’s in-licensed atherosclerosis drug AGI-1067, which he believes remains a risky project. Earlier this week, Malik suggested AstraZeneca could benefit from buying fellow UK-headquartered company Shire to bolster its R&D portfolio.