The combination formulation was approved for medical use in the United States in 2002.[2][6] In the United States the wholesale cost as of 2017 is between US$2.32 and US$3.15 per day.[7] In the United Kingdom a similar dose costs the NHS £0.90 to £2.72 per day, according to 2015 data.[8] A generic version was approved in mid 2018.[9] In 2017, it was the 288th most commonly prescribed medication in the United States, with more than one million prescriptions.[10][11]