World number-two Andy Murray said that tennis needs more drug testing, after Maria Sharapova's positive test for meldonium, and questioned the Russian's use of the drug for medical purposes.

"I think all sports can do more, I think it's better than it was a few years ago," Murray told reporters at the Indian Wells tournament in California on 10 March. "Last year I certainly got tested a lot, but this year I've been tested once, twice, so far this year, and we're three months into the year."

Meldonium, produced in Latvia but unavailable for purchase in the United States where Sharapova is based, was only added to the World Anti-Doping Agency (Wada) list of banned substances in January, shortly before her positive test at the Australian Open. Manufactured for people suffering from heart problems, it can also increase blood flow and improve exercise capacity.

Sharapova is provisionally suspended by the International Tennis Federation from 12 March and faces up to a four-year ban. She said she was first given the drug by a family doctor 10 years ago after she frequently became sick, had irregular electrocardiogram results, a magnesium deficiency and a family history of diabetes.

"I read that 55 athletes have failed tests for that substance since January first," said Murray. "You just don't expect high-level athletes at the top of many different sports to have heart conditions," he added.

The highest-paid woman in sports, Sharapova has already lost support from some sponsors, with Swiss watchmaker TAG Heuer cutting ties this week, while Nike and Porsche have distanced themselves from her.

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Andy Murray