Sales of Takeda's diabetes drug Actos rose 13% in the two weeks after the Cleveland Clinic issued a report suggesting competitor GlaxoSmithKline's Avandia raised the risk of heart attacks by 43 %.
The number of prescriptions for Avandia fell to 151,807 in the week ending June 1, according to Wolters Kluwer Health cited by Bloomberg News. By contrast, Actos prescriptions rose to 265,723 the last week of May.
The FDA has asked both GSK and Takeda to strengthen warnings on their drugs' labeling about the risk of heart failure.
Since then, shares of Takeda have fallen 4.6% on the Tokyo Stock Exchange, while Glaxo shares recouped some of their loss, rising 2.2 % in London.
Avandia, designed to treat Type 2 diabetes is GSK’s second-best selling drug with $3.3 billion in global sales last year. Actos, with global sales of $2.8 billion, accounted for a quarter of Takeda's revenue last year and was the company's best seller.