Washington, Nov 10 (ANI): Pop star Britney Spears has been ordered by the court to be available on the phone to drug testing authorities.

Spears' ex-husband Kevin Federline's attorney Mark Kaplan complained that the singer, who has been ordered by the court to undergo two tests every week, had not responded to 8 out of 14 calls for drug tests, reports Contactmusic.

According to court orders, Spears is required to respond to requests from the testing authorities within an hour.

At a previous hearing, the court had said that a missed drugs check would be seen as a failed test.

Spears' lawyer Anne Kiley said that her client could not be contacted because of changed telephone numbers.

She also added that it was not fair to assume that Spears was consuming drugs if she could not be reached, insisting that the star had to change her number frequently due to the pressures of being a celebrity.

The judge therefore said that the singer could change her number as frequently as she wanted, but ordered her to keep the authorities updated on her contact details. (ANI)