GlaxoSmithKline has joined the list of companies which are suing Abbott Laboratories over the US firm’s decision, taken almost four years ago, to substantially increase the price of its HIV treatment Norvir.

In a lawsuit filed with the US District Court in Oakland, California, and reported by the Wall Street Journal, GSK is claiming that Abbott "schemed” to take away “one of the critical components" of AIDS drug cocktails by increasing the price of Norvir (ritonavir) by some 400% in December 2003. The wholesale cost of the treatment in the USA, which is used as a boosting agent for other protease inhibitors, subsequently rose to $257.10 from $51.30 for 30 100mg capsules.

However Abbott did not raise the price of its own HIV combination treatment Kaletra (lopinavir/ritonavir), which includes Norvir and GSK alleges that the rise happened two weeks after the latter introduced its HIV drug Lexiva/Telzir (fosamprenavir), which is used in combination with Abbott's treatment. The cost of Lexiva shot up and "Abbott's anticompetitive scheme protected Kaletra against new competitors that threatened its market dominance, in violation of the antitrust laws," GSK claims.

The price rise four years ago caused uproar at the time and Abbott settled lawsuits in 2004 filed by the AIDS Healthcare Foundation. The company also faces a separate class-action lawsuit on behalf of consumers and third-party payers and just last month Walgreen, Safeway, The Kroger Co, New Albertson's and American Sales Co also filed suit in California.

Abbott is nonplussed by these cases and spokeswoman Melissa Brotz told the WSJ that GSK’s “frivolous lawsuit is completely without merit," and the firm has always maintained that the price rise represented the value of the drug.

These latest lawsuits follow an article published earlier in the year from the WSJ which reported that Abbott discussed two alternatives to a Norvir price increase. One was to sell the drug only as a liquid, which one executive said “tasted like vomit” and would have discouraged use of Norvir when used in other products. Another was to pull Norvir from the market altogether, but Abbott said that it never seriously considered those scenarios and the latter firm has also pointed out that competitors' drugs have since gained market share.