Watson Pharmaceuticals also announced Wednesday that it launched an authorized generic version as part of an exclusive agreement with Pfizer, which will continue to manufacture the drug and will get a share of Watson's net sales. 

WellPoint, the largest U.S. health insurer by enrollment, told Bloomberg Thursday it will put Watson's version of the drug on its generics list.

Lipitor's patent expiration could mark the beginning of the end of a huge patent era for many best-selling drugs. According to Roland Berger Strategy Consultants, almost 75 percent of 2008 global pharmaceutical sales will go off patent within five years — nearly $100 billion dollars worth of prescription drugs.

Sales of Pfizer's prescription drugs are predicted to decline from $54.1 billion last year to $51.2 billion by 2016, according to an EvaluatePharma report published this summer.

The report also estimates $139 billion will be lost from sales of branded drugs between 2011 and 2016, equal to 20 percent of the global pharmaceutical market last year. Meanwhile the race for the pharmaceutical sales top spot is going to be close, with Sanofi and Novartis breathing down Pfizer's neck – all three companies are expected to have prescription drug sales in the region of $50 billion by 2016.

Meanwhile, as Lipitor's reign comes to an end, rheumatoid arthritis treatment Humira will assume the crown as the world's top selling drug, while Pfizer will rank as the biggest seller of prescription medicines through to 2016.

According to the Associated Press, Pfizer is not giving up its behemoth easily. "Pfizer has devised discounts and incentives for patients, insurers and companies that process prescriptions that will, at least for the next six months, make the brand name drug about as cheap as or cheaper than the generics. Pfizer also has spent tens of millions of dollars this year on marketing to keep patients on Lipitor," writes AP staff writer Linda A. Johnson.

Pfizer's effort includes:

• Offering insured patients a discount card to get Lipitor for $4 a month, far below the $25 average copayment for a preferred brand-name drug and below the $10 average copay for a generic drug. Pfizer is promoting this heavily through ads, information distributed at doctors' offices and its www.LipitorForYou.com site. Pfizer, based in New York, said Tuesday that sign-ups have exceeded its goals.
• Paying pharmacies to mail Lipitor patients offers for the $4 copay card and to counsel patients that Lipitor lowers bad cholesterol more than rival drugs and helps prevent heart attacks and strokes.
• Keeping U.S. marketing spending nearly level until the last minute, versus the typical two-thirds drop in a drug's final year under patent. From July through September, Pfizer spent almost $90 million on doctor sales calls and free samples, about the same as a year earlier, according to Cegedim Strategic Data. Ads targeting patients fell about 60 percent to $19 million. All that will soon taper off.
• Negotiating unusual deals with some insurance plans and prescription benefit managers, the companies that process prescription claims for insurers or employers, to block pharmacists from dispensing generic Lipitor. Pfizer is giving them rebates that bring their cost for Lipitor down to the price of a generic or slightly less — if they agree to dispense only Lipitor for the six months before additional generic competition slashes prices. The move has generated some controversy and means many of the 3 million Americans taking Lipitor won't be able switch to the generic.

What do the deals mean for consumers? AARP says, "It may depend on whether they are covered by employer plans or other private health insurance companies, by Medicare Part D drug plans, or not insured at all. UnitedHealthCare, for example, one of the nation's largest insurers, has said that it will charge enrollees a higher copay for the generic than Lipitor."

A look ahead: Top 10 selling products in 2016 (souce: EvaluatePharma)

1. Humira (arthritis)
2. Avastin (cancer)
3. Rituxan (cancer)
4. Crestor (cholesterol)
5. Enbrel (arthritis)
6. Seretide/Advair (asthma/COPD)
7. Januvia/Janumet (diabetes)
8. Herceptin (cancer)
9. Remicade (arthritis)
10. Prevnar (Pneumococcal disease)