The United States Anti-Doping Agency on Thursday also disputed that Mayweather violated any rules, saying the boxer applied for and was granted an exemption for the infusion.
"As already confirmed by the USADA statement, I did not commit any violations of the Nevada or USADA drug testing guidelines," Mayweather said in a statement. "I follow and have always followed the rules of Nevada and USADA, the gold standard of drug testing.
"Let's not forget that I was the one six years ago who insisted on elevating the level of drug testing for all my fights. As a result, there is more drug testing and awareness of its importance in the sport of boxing today than ever before. I am very proud to be a clean athlete and will continue to champion the cause."
Mayweather's IV usage, reported Wednesday by SB Nation, was allowed by USADA despite it being against the very WADA rules that USADA claims to follow.
The contract that Mayweather and Pacquiao signed with USADA to cover the drug testing protocol for the bout allowed for therapeutic use exemptions, but USADA issued Mayweather's exemption for the IV use three weeks after the fight, which is unusual.
In addition, USADA did not notify the Nevada State Athletic Commission, the regulatory agency overseeing the fight, or Pacquiao's team until after it was granted well after the fight, something NSAC executive director Bob Bennett took major issue with.
Bennett said only the commission can grant a therapeutic use exemption (TUE) to an athlete, not a drug testing body such as USADA.
"Although Mr. Mayweather's application was not approved until after his fight with Mr. Pacquiao and all tests results were reported, Mr. Mayweather did disclose the infusion to USADA in advance of the IV being administered to him," USADA said in its statement earlier Thursday. "Furthermore, once the TUE was granted, the NSAC and Mr. Pacquiao were immediately notified even though the practice is not prohibited under NSAC rules."
The controversy over Mayweather using IV injections that are not WADA compliant comes just days before he is scheduled to defend the welterweight world title against Andre Berto on Saturday night at the MGM Grand in what Mayweather has said will be the final bout of his 19-year career.
Mayweather's medical team told the USADA collection agents that the IV -- which reportedly included a mixture of 250 milliliters of saline and multivitamins and a 500-milliliter mixture of saline and Vitamin C -- was being given to Mayweather for rehydration purposes following the weigh-in.
The fact that they were given intravenously was not allowed, according to WADA rules that state intravenous infusions or injections of more than 50 milliliters per six hours are prohibited "except for those legitimately received in the course of hospital admissions, surgical procedures, or clinical investigations."
WADA bans such large injections and infusions because they can be used to "dilute or mask the presence of another substance."
While Mayweather was given an exemption three weeks after the fight, Pacquiao was denied a request by the NSAC to be injected with the legal painkiller Toradol on fight night to ease pain in his injured rotator cuff, for which he had surgery after the bout.
Pacquiao's camp was upset about the situation.
"I find it ironic. We tried to get an injection that was totally legal before the fight and the commission slams us and then this thing with Mayweather happens," Michael Koncz, Pacquiao's adviser, told ESPN. "We need to fight in Vegas again so I don't want to make many more comments but it is unusual and it was never disclosed to us until quite a ways after the fight.
"Maybe the best thing for Floyd to do is have a rematch with Manny. But we were shocked by [the TUE]. It shouldn't have happened."
Top Rank chairman Bob Arum, Pacquiao's promoter, also was upset by the situation.
"USADA has a lot of explaining to do," Arum told ESPN. "When we learned about this I was outraged. But I can't just bay at the moon. What legal redress do we have? I have the information, our lawyers got it, but what were we supposed to do with it? Ask for the decision to be reversed? I really think people have to look closely at USADA and investigate what's going on with them."
Arum also said the reason he didn't go public when he received the news that Mayweather had been granted the TUE retroactively because he was bound by a confidentiality clause in the contract with Mayweather. But once the matter became public, he discussed it.
"Our lawyers told us that the information tramsmitted to us was confidential and we were not allowed to disseminate it, so based on that advice we said nothing [until it came out]," Arum said.
When Mayweather and Pacquiao initially began negotiating a fight in late 2009, it fell apart over a disagreement on drug testing protocol, which became a major hurdle in making the fight. After Mayweather accused Pacquiao of using performance-enhancing drugs, Pacquiao sued him and Mayweather eventually settled for an undisclosed seven-figure settlement.
Mayweather used banned IV before Pacquiao fight
ESPN senior boxing writer Dan Rafael reacts to the report that Floyd Mayweather used a banned intravenous injection before his superfight with Manny Pacquiao.