Pharmaceutical major Pfizer has announced a 50% slump in net income for Q4 2011 as the company suffers at the hands of generic versions of its cholesterol blockbuster Lipitor.

Turnover fell 4% to $16.75bn, with sales of Lipitor falling 24% to just under $2bn. The loss of patent protection in the US had a significant impact; sales there fell 42%.

Other Pfizer treatments reported mixed results, with Viagra and Celebrex increasing by 5% and 7% respectively in contrast to Norvasc and Xalatan, which reported respective falls of 6% and 37%.

Indifferent results were also reported from within the portfolio of drugs acquired through the company’s purchase of Wyeth, designed to offset the impact of Lipitor’s patent expiry.

Although pneumococcal vaccine Prevnar/Prevenar and arthritis medication Enbrel witnessed gains of 1% and 7% respectively, antidepressant Effexor XR fell 32% and antibiotic Zosyn/Tazocin decreased some 28%.

Pfizer chief executive Ian Read said, "Overall, 2011 was a year of setting new direction and focus for Pfizer. I am pleased with our 2011 financial performance, which was achieved in the face of a challenging global market and product losses of exclusivity of approximately $5bn."