More details about the $41 billion (£25 billion) Merck acquisition of Schering-Plough are being sought by the US Federal Trade Commission on anti-trust grounds.
Since the deal will create the world’s second-largest drugmaker by revenue, both companies have said that they expected the request and intend to fully cooperate.
The deal was brokered in March, and both companies expect it to be finalised in the fourth quarter of this year after approval by both sets of shareholders.
The combined companies field top-level medications, including Singulair for asthma, Nasonex for allergies and the cholesterol drugs Zetia and Vytorin.
Merck plans to issue about $3.5 billion (£2.2 billion) of debt to fund the buyout, with some of the proceeds being used for Vioxx lawsuit-settlement funds.
This relates to personal injury claims connected to incidents of myocardial infarction and ischemic stroke allegedly associated with the drug, and which are currently before the US courts.
Copyright Press Association 2009