"I think that tennis is doing a good job in the programmes it has and we've had two fairly high-profile cases recently with Marin Cilic and Viktor Troicki and let's not forget both of those cases resulted in violations for the athletes concerned," the ITF's anti-doping manager Stuart Miller said on Thursday.
"To me that shows that the programme is successful in catching the people it is supposed to be catching so I don't think it's necessarily fair criticism," he told Reuters at the World Conference on Doping in Sport.
"Our programme includes in-competition and out-of-competition testing, with both urine and bloods samples taken and the recent introduction of the athlete's biological passport, another tool in the fight against doping. We have also been increasing our proportion of out-of-competition testing."
Serbia's world number two Djokovic said he had lost all trust in the sport's anti-doping programme following compatriot Troicki's 12-month ban for failing to provide a blood sample at the Monte Carlo Masters in April after complaining of feeling unwell.
Troicki said he believed he could be excused from the test if he provided a reason to the ITF.
Last week, Federer said he felt players were not being tested enough.
"I feel like I used to get tested more, I think I was tested 25 times in 2003, 2004. Ever since, I think it's been clearly going down this season," the 17-times grand slam winner told reporters at the ATP Tour finals in London.
But Miller said there had been no real change in the number of times the ITF had tested the Swiss.
"We've got the exact number of tests on Roger Federer and our information does not match what he says.
"As far as we are concerned, the number of tests completed have remained remarkably constant," added Miller.
"That isn't to say that there aren't other organisations that were testing him to some extent previously and now doing so less and we just don't know about those figures, but as far as we are concerned the number of tests remains pretty constant for 10 years or so."
The ITF is responsible for the enforcement, management and administration of the anti-doping programme on behalf of all professional tennis.
"I'm confident the tennis anti-doping programme is using all the tools available to it to maximise its efficiency but we must remember, you also need a deterrent effect and prevention effect and education as well," Miller said.
Croatian Marin Cilic recently completed a four-month ban for taking the stimulant nikethamide. Cilic said he had taken the substance inadvertently in glucose tablets.
- Sports & Recreation
- Marin Cilic
- Viktor Troicki
- Stuart Miller