Four trade union health insurance plans and a consumer group have launched legal action against eight pharmaceutical companies over the use of coupons for drug co-payments, claiming them to be illegal and responsible for increases to long-term healthcare costs.

The lawsuits were filed in federal courts in Philadelphia, New York, Newark and Chicago, US, and named Abbott Laboratories, Amgen, AstraZeneca, Bristol-Myers Squibb, GlaxoSmithKline, Merck, Novartis and Pfizer.

The action is being sought by healthcare plans for American Federation of State, County and Municipal Employees District Council 37, the Sergeants Benevolent Association, the New England Carpenters and the Plumbers and Pipefitter Local 572.

One particular complaint, made by a plaintiff’s lawyer Lisa J. Rodriguez, cited a recent study as estimating that these kickbacks will increase health benefit providers’ prescription drug costs by $32bn over the next decade.

Pharmaceutical companies have issued drug coupons in order to tempt patients into continuing the use of brand-name drugs rather than switching to cheaper generic versions, especially as a number of high-profile drugs suffer from patent expiries.

Arguably the most notable has been Pfizer’s issue of coupons for its cholesterol blockbuster Lipitor, which saw its patent protection expire in November 2011.

Pfizer spokesman Chris Loder defended the use of drug coupons in a company statement, announcing that Pfizer intends to fight the claim.

"Given the larger cost-sharing burden being placed on patients, Pfizer supports the use of company-sponsored programs which help patients with out-of-pocket expenses for the medicines prescribed by their physician," said Loder.