"It's been the busiest 18 months I can remember," says Latham & Watkins California partner Charles Ruck of activity in the pharmaceutical sector. "Even the recent gyrations on the stock market don't seem to be slowing people down."

He is not exaggerating. Data from Mergermarket shows that in the three years to 31 July 2015, global deal value in the sector has soared, with £201bn of deals announced worldwide over the most recent year, compared with £68.4bn in the year to 31 July 2013 and £92.2bn over the same period in 2014. With deal values climbing, five of the 10 largest deals over the three year period have been announced since January this year.

Latham tops the global and European legal adviser rankings by value and volume, with all of the tables dominated by US players. The firm advised on 53 deals globally worth a combined £162.5bn over the three year period, making it the most active firm by both value and volume of mandates,  working on more than 40% of the total transaction value. Skadden Arps Slate Meagher & Flom came second globally by both measures, with a deal count of 45 mandates worth a combined £148m.

Overall, US firms held the top 10 spots in the global rankings by volume and eight of the top 10 by value. Non-US firms fared only a little better in the European rankings, holding only 10% of the top spots by value and 40% by volume.

Given its position at the top of the tables, Latham has advised on many of the most high profile deals over both the last three years and the year to date. Its haul includes roles on six of the 10 biggest deals globally since 2012, including the biggest deal of the period – Actavis's £40bn acquisition of Allergan last year. More recent mandates include advising Kythera Biopharmaceuticals on its $2.1bn (£1.3bn) sale to Allergan, and Receptos on its acquisition by pharmaceuticals company Celgene Corporation for $7.2bn (£4.6bn) last month.

Fellow Latham Orange Country corporate partner Scott Shean, who led alongside Ruck on both of the most recent deals comments: "There have been a handful of super deals which have really driven up dollar growth."

Bucking the trend for US domination of the sector though, two Irish firms appear in the global value rankings. Arthur Cox and Matheson feature in ninth and tenth place by value thanks to their roles on the Actavis/Allergan deal on which Matheson corporate partners George Brady and Patrick Spicer led the team advising Allergan.

Arthur Cox advised Actavis with corporate partner Geoff Moore at the helm. Moore comments: "For decades we've been lucky enough to act for a host of pharma companies who set up in Ireland in the 1970s. It's an extremely hot sector, and there will undoubtedly be further opportunities to act on other pharma deals."

Global giant Baker & Mckenzie, which came fourth in the league table by deal count, recently carried out research into predicted growth in the sector.

The report, published in association with Oxford Economics in July this year, found that the pharmaceutical and healthcare sectors will continue to see significant M&A activity over the next five years.

It predicts an estimated US$510bn in completed pharmaceutical deals will take place in 2015, up from $115.8 bn in 2014. Strong activity of more than $300bn per year is expected to continue in 2016 and beyond as pharmaceutical companies use M&A to expand into new markets.

Jane Hobson, Bakers'  global healthcare leader explains: "Transactional activity in the pharmaceutical industry has grown enormously and one factor is the growth in the demand for drugs in emerging economic markets. Governments want to improve and increase the availability of healthcare for their populations and offer the same medical technology that the more developed markets have."

"We've seen a change in the approach of the pharma companies as they continue to face issues with expiring patents – they're looking to find growth elsewhere and are focusing on their core strengths which has led to larger deal activity."

"There's also been consolidation of generics deals, the most recent example being when Allergan sold their generic drugs business to Teva Pharmaceutical Industries in July this year."

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