This is despite pressure from fellow Republicans and talk of who might replace him on the November 6 ballot.
Akin – a staunch abortion opponent – vowed to stay in the contest against Democratic Senator Claire McCaskill, indicating he represents a conservative movement that must be heard.
A 5pm local time deadline passed with no indication he planned to take his name off the ballot.
Akin was defiant. His campaign posted a new website on Tuesday seeking donations with a banner "I'm pro-life and I stand with Todd Akin." It had briefly featured a picture of a foetus and a picture of McCaskill with US President Barack Obama, but the foetus image was later removed.
"We are going to continue in this race for US Senate," Akin told The Mike Huckabee Show, a radio programme hosted by the former Arkansas governor.
Republican presidential candidate Mitt Romney on Tuesday joined the chorus calling for him to pull out of his race after Akin claimed in a weekend television interview that it was extremely rare for women to get pregnant from "legitimate rape".
"Today, his fellow Missourians urged him to step aside and I think he should accept their counsel and exit the Senate race," said Romney, who previously condemned Akin's comments.
The outrage over Akin's remarks sent waves of anxiety through the Republican Party a week before it reaches out to independent voters, especially women, at its national convention where it will nominate Romney to run against Obama.
Waves of anxiety
Republicans fear the Akin episode could prevent them from winning in Missouri, reducing their chances of picking up the four seats they need ensure a majority in the 100-member Senate.
McCaskill had trailed Akin by about 10 points but a Public Policy Polling survey on Monday had Akin ahead by one point.
To the dismay of many Republicans, Akin's woes have cast a spotlight on a part of the platform party members again endorsed on Tuesday: a call to oppose abortion with no mention of exceptions in cases of rape and incest.
That is not the position of Romney, who has said abortion should be allowed to end pregnancies resulting from rape or incest.
Obama, who supports abortion rights, also strongly denounced Akin's remarks, saying "rape is rape".
Romney's vice presidential running mate, US Representative Paul Ryan of Wisconsin, has expressed a harder line on abortion, saying it should be allowed only to save the life of the mother. The campaign said this week a Romney/Ryan administration would reflect Romney's position.
Ryan, who has co-sponsored anti-abortion legislation with Akin, called the Missouri candidate and suggested he think about leaving the Senate contest. "He thought I maybe should give some thought to stepping down, but he didn't tell me what to do. And that's because he's a very respectful and a very decent guy," Akin said on the Sean Hannity radio programme.
Coming to Akin's defence
The controversy is a distraction in a campaign Romney has sought to keep tightly focused on the economy and jobs.
Tim Wildmon, president of the influential American Family Association, was one of several social conservatives who have come to Akin's defence.
"This is a decent, honourable man who has been pro-life and pro-traditional values. He has apologised for his choice of words and that should be the end of it," Wildmon said.
Although religious conservatives are a crucial part of the Republican base, many party leaders say its central message should be its conservative approach to fiscal issues like debt and deficits.
"It's not that we keep shooting ourselves in the foot. We keep shooting ourselves in the eyes," said former Missouri Senator John Danforth, one of a group of current and former US senators from the state who urged Akin to step aside.
Under Missouri election law, Akin had until 5pm local time to get his name off the ballot for the November 6 election most easily. But he faces a harder deadline on September 25, the last day his name can be removed with a court order.
If Akin withdraws, the Missouri Republican committee would name a successor to run against McCaskill. Possible candidates include the two Republicans Akin defeated in the primary just two weeks ago – St Louis businessman John Brunner and former state Senator Sarah Steelman.
But the party can pick any candidate.
Other possibilities include former Senator Jim Talent, who lost narrowly to McCaskill in 2006 and Representative Jo Ann Emerson, considered a favourite because many Republicans think the party would best reassure women voters by running a woman.
In another sign that he is not leaving, US News and World Report reported that Akin spent $150 000 on Tuesday for television advertisements in seven media markets.
But he will struggle to keep up with McCaskill, especially after the Karl Rove-linked American Crossroads Super PAC and the Republican Senate committee said they would hold back millions in funding earmarked for the race.
McCaskill's campaign is using Akin's comments in its fundraising. Emily's List, which supports Democratic women candidates, said it has seen a big jump in fundraising.
Akin apologised again in an internet advertisement called "Forgiveness". And he sent a fundraising letter to supporters on Tuesday asking for donations of $3 or more. – Reuters