[Editor's note: This story has been updated as more companies have pulled their ads.]

The outcry over right-wing radio personality Rush Limbaugh’s rude comments on a law student’s sex life has cost him at least 19 advertisers. Some have dropped their specific ad buys on the show, at least five others have suspended their ads, even after he apologized twice. Other companies, whose media buys happened to place their ads during Mr. Limbaugh's show, have publicly stated that they are ensuring that they don't appear there again.

How much more erosion of his advertising base can he afford?

Probably a lot more, if he can hold onto his audience and survive the immediate reaction from shareholders of Clear Channel, which produces the show.

"As long as the Limbaugh show maintains its ratings and notoriety, there will be advertisers eager to utilize it," writes Michael Harrison, publisher of industry trade magazine, Talkers, in an e-mail. “I would imagine Clear Channel is already picking up new sponsors to replace the ones that have publicly defected and I wouldn't be surprised if some of those that have cancelled come back after the dust has settled.... The American advertising industry is not necessarily known for its taste or dignity.”

Departing sponsors include LegalZoom, ProFlowers, Citrix, Quicken Loans, Sensa, Sleep Number beds, and Carbonite. Others, including AOL and Tax Resolution Services, have “suspended” their advertising on the show. Sears, AutoZone and Allstate have all said they do not sponsor Limbaugh’s show and advertisements for the companies that appeared on the program were placed there by mistake.

Limbaugh got the controversy started last Wednesday when he impugned Georgetown University’s Sandra Fluke on the air, calling her a “slut” and a “prostitute” after she appeared before a congressional committee arguing that her school’s health coverage should include birth control. Limbaugh later in the week insisted that the public should have access to video of her sexual encounters in exchange for the alleged funding of her birth control.

The comments struck many as extraordinarily crass, even for Limbaugh, who frequently makes derisive ad hominem attacks against those he disagrees with. A boycott movement quickly took root, spreading across online communities on sites like Reddit and Facebook, and the strong reaction against Limbaugh inspired seven sponsors to pull ads.

Carbonite CEO David Friend wrote on his company’s blog: "No one with daughters the age of Sandra Fluke, and I have two, could possibly abide the insult and abuse heaped upon this courageous and well-intentioned young lady. Mr. Limbaugh, with his highly personal attacks on Ms. Fluke, overstepped any reasonable bounds of decency. Even though Mr. Limbaugh has now issued an apology, we have nonetheless decided to withdraw our advertising from his show."

Limbaugh himself apologized in a statement Saturday and again on his show, Monday, saying that he wanted to “sincerely apologize” to Fluke for “using those two words to describe her.”

But he also struck back at critics, saying that he would replace those advertisers with others.

The big question is how Clear Channel reacts to the controversy. Unlike Limbaugh, the San Antonio-based company has quarterly revenue targets to meet and has to be concerned about the immediate reaction of shareholders. Clear Channel operates 866 stations in 150 markets in the United States. Its Premiere Networks handles 90 syndicated programs, which it distributes to approximately 5,800 affiliate stations.

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So far, Clear Channel has not commented on the controversy.

"The question and focus should be on how many listeners Rush might lose because of this," Mr. Harrison says. "Ironically, his ratings will probably increase due to all this attention. If that happens his sponsorships will actually increase."