An “unprecedented” number of brand-name drugs are currently going off patent, representing more than $49 billion in US sales through 2011, according to major pharmacy benefit manager Medco Health Solutions, which forecasts that US consolidated generic dispensing rates will exceed 60% in the near future.

This year alone, 14 major drugs are set to lose patent protection in the USA, 10 of which have revenues exceeding $8.1 billion, for example Sanofi-Aventis’ leading sleep medication Ambien (zolpidem) and two antihypertensives – Pfizer’s Norvasc (amlodipine besylate) and AstraZeneca’s Toprol XL (metoprolol succinate extended-release).

Ambien’s loss of patent protection could dramatically reshape spending on insomnia treatments during 2007, given that its US sales exceeded $2 billion last year; combined with the controlled-release version, Ambien CR, total volume rose 38.1%, says Medco. Medications to treat sleep disorders are one of the fastest growing categories of drug spending and, while seniors are the most prevalent users of hypnotics, the number of adults aged 20-44 using sleep medications rose 128% during 2000-5, it adds.

Heavy sales impact for pharmacos

The US patent on Norvasc, the top-selling calcium channel blocker, expires in September, and the impact on Pfizer’s sales in that market is expected to be very significant, according to a report by Datamonitor. When the product’s patent in the UK expired, sales there decreased more than 50% during 2004-5, says the study.

Toprol XL’s US patent ends on September 18, but it is already subject to generic competition due to a January 2006 US District Court decision in favour of a group of generics makers which claimed that the patents on the drug were invalid and unenforceable. However, AstraZeneca has agreed a deal with Par Pharmaceutical to distribute an authorised generic version of the drug.

Hypertension affects about 60 million adults in the USA, and Norvasc and Toprol XL are the third and fourth most frequently dispensed drugs in the USA, respectively, says IMS Health. Together with GlaxoSmithKline’s Coreg (carvedilol), whose US patent expired this month (March), these three drugs combined generated total US sales of $4.8 billion in 2006.

This year’s patent expiries follow those of several blockbusters in 2006, which included two cholesterol-lowerers – Merck & Co’s Zocor (simvastatin) and Bristol-Myers Squibb’s Pravachol (pravastatin), plus Pfizer’s depression/anxiety treatment Zoloft (sertraline), GlaxoSmithKline Flonase (fluticasone propionate) for nasal allergies and Boehringer Ingelheim’s nonsteroidal anti-inflammatory Mobic (meloxicam).

10 major drugs over next five years to lose patents

And, over the next five years, an average of 10 major drugs will lose US patent protection each year, a new study from Urch Publishing has estimated. The most notable casualty will be Pfizer’s cholesterol-lowerer Lipitor (atorvastatin) - the world’s top-selling drug with sales last year of almost $13 billion - which will start losing protection outside the USA from March 2010. Lipitor also led the US market in 2006, with sales of $8.3 billion, and was the leading US product in terms of dispensed prescriptions, which were worth $74 million, says IMS.

US expiries in 2008 will include Merck & Co's Fosamax (alendronate), GlaxoSmithKline’s Advair (fluticasone propionate/salmeterol), Pfizer’s Zyrtec (cetirizine) and Wyeth’s Effexor XR (venlafaxine). In 2009, the US patent on TAP Pharmaceutical’s Prevacid (lansoprazole/amoxicillin/clarithromycin) ends, and Merck & Co’s Cozaar/Hyzaar (losartan/losartan plus hydrochlorothiazide) expires there in 2010.

55.2% of all medications dispensed to Medco members in 2006 were for generics, an increase of 3.7% over 2005, says the firm. “When a new generic drug is close to entering the market, we communicate to our clients, their members and health care providers by mail, fax, phone and e-messaging to help ensure that they take advantage of the savings opportunity immediately,” said Laizer Kornwasser, senior vice president of channel and generic strategy at Medco. “Through our mail-order pharmacy we can achieve a 95% generic substitution rate within the first week of the brand losing patent protection,” he added.