Merck & Co saw revenues slip 4 per cent in the third quarter as diabetes blockbuster Januvia continued to show signs of weakness in the US.

Group sales came in at $11 billion, with Merck's DPP-4 inhibitor Januvia (sitagliptin) down 5% to $927 million as growth outside the US failed to support a decline in domestic sales. Line extension Janumet (sitagliptin and metformin) fared a bit better, up 9% to $442 million.

Januvia is jostling in the marketplace alongside other DPP-4 inhibitors - such as Eli Lilly's Tradjenta (linagliptin), AstraZeneca/Bristol-Myers Squibb's Onglyza (saxagliptin) and Takeda's Nesina (alogliptin) - as well as new entrants like Johnson & Johnson's SGLT-2 inhibitor Invokana (canagliflozin) which has got off to a strong start since being approved in the US in March.

Merck's president of human health Adam Schechter said the overall diabetes market in the US is flat and "with significant new competition, we must defend market share."

Elsewhere, HIV drug Isentress (raltegravir) shrugged off a tougher competitive environment to reach $427 million, a rise of 7%, while sales of the cervical cancer vaccine Gardasil climbed 15% to $665 million thanks to increasing use by males in the US.

The sales declines for Merck's cholesterol drug drugs Vytorin (ezetimibe plus simvastatin) and Zetia (ezetimibe) slowed a little in the third quarter - down 1% collectively to $1.1 billion, with a small gain of Zetia offsetting declines for Vytorin.

The company's anti-inflammatory products stole the show in the quarter with Remicade (infliximab) - the Johnson & Johnson drug which Merck sells outside the USA -  up 17% to $574 million and Simponi (golimumab) advancing 46% to $126 million, although the latter was just marginally up on the second quarter of this year.

Earnings per share (EPS) showed the strain of the $2.2 billion in acquisition and restructuring costs in the quarter, falling to $0.38 from $0.56 a year earlier.

Merck said earlier this month it plans to cut another 8,500 jobs - on top of 7,500 already announced - to reduce its costs by $2.5 billion by 2015 and improve competitiveness.

Commenting on that programme, chief executive Kenneth Frazier said it hinged upon "sharpening our focus on R&D" - spending on which dropped $260 million this quarter - and prioritising the commercial elements of the business that will drive growth such as vaccines, diabetes and its oncology portfolio such as much-touted anti-PD1 drug MK-3475.

He intimated that other deals such as the $1 billion sale of older drugs and a manufacturing plant to South Africa's Aspen could be on the cards. Some investors have been pushing for Merck to divest businesses such as consumer health and veterinary medicines and focus on its prescription pharma operations.