Drugs giant GlaxoSmithKline yesterday admitted to “unacceptable” mistakes in the United States following its recent £1.9bn fine to settle the largest healthcare fraud in American history. Announcing interim results, chief executive Sir Andrew Witty said he was “very sorry” for the group’s actions after Glaxo pleaded guilty this month to mis-promoting two medicines by seeking to persuade doctors to prescribe anti-depressant drug Paxil for children although it was not intended for under 18s and pushing the Wellbutrin drug for unapproved uses.