“In the 40 years I have been involved in athletics, there have been big moments — Ben Johnson, Marion Jones,” the British middle-distance great told the BBC.
“This is up there.”
The sport’s governing body is investigating allegations by a German TV station of a cover-up of systematic doping in Russia.
Two IAAF officials have stepped down while the investigation takes place.
“It’s been described as a bad week for athletics,” said Coe, who recently declared his candidacy to become president of the IAAF.
“I would go further, it’s been a ghastly week.
“None of us should hide or shy away from that. We have to bring this tawdry, sorry episode and any of those allegations to a close as quickly as we can.”
Johnson failed a doping test after winning the 100 metres at the Seoul Olympics in 1988.
Jones was stripped of five Olympic gold medals in 2007 after admitting to using performance-enhancing drugs in her career.