A dramatic decline in sales of asthma drug Singular led to a 4 per cent drop in revenues at Merck & Co to $11.5bn, a little below analysts' forecasts.
On balance however the performance in the quarter was positive, with the pharma company's cost-reduction drive helping it achieve a 2 per cent increase in net income to $1.73bn, which topped expectations.
Merck's chief executive Kenneth Frazier said the company was on track to meet its target of bringing in 2012 revenues at around 2011 levels, noting that with one quarter remaining year-to-date sales were up 2 per cent on last year.
Singulair (montelukast) lost patent protection in the US in August, and the generic onslaught slashed sales by 55 per cent to $602m in the third quarter, down from $1.4bn in the previous three months.
The product - which was the fourth-largest drug in the world earlier this year - is expected to slide even further when it loses patent protection in Europe next year.
Singulair's decline was offset partially by gains for other products, notably diabetes treatment Januvia (sitagliptin) which rose 15 per cent to $975m - making it Merck's top-selling product for the first time. Line extension Janumet (sitagliptin plus metformin) added 16 per cent to reach $405m.
Also making gains were human papillomavirus (HPV) vaccine Gardasil, which saw a 31 per cent hike to $581m attributed by Merck to increased use of the product in males, and herpes vaccine Zostavax which rocketed more than 80 per cent to $202m.
HIV drug Isentress (raltegravir) also did well with sales up 16 per cent to $399m, as did oral hepatitis C drug Victrelis which grew to $149m in the quarter versus $31m a year ago.
Cholesterol franchise Zetia (ezetimibe) and Vytorin (ezetimibe plus simvastatin) slipped a little in the quarter - down 1 per cent to $1.1bn, with a gain for Zetia offset by declines for Vytorin.
Similarly, Merck's antihypertensive drugs Cozaar (losartan) and Hyzaar (losartan plus hydrochlorothiazide) continued to succumb to generic competition with a decline of 27 per cent to $295m.
Frazier said that the performance of new products, plus gains in emerging markets, where sales grew 16 per cent, and a healthy pipeline of new products meant that Merck was on track to "drive long-term growth and shareholder value".