Russia's athletics federation was this week provisionally suspended from international competition, including the Olympic Games, for its alleged involvement in widespread doping.
Coe said action needed to be taken against Russia or there were "unlikely to be many tomorrows for athletics".
"It was the toughest sanction we had," Coe wrote in the Sunday Telegraph.
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The International Association of Athletics Federations council members voted 22-1 in favour of Russia being banned after the publication of an independent World Anti-Doping Agency report that alleged "state-sponsored doping".
Coe, who became president of the sport's world governing body in August, said the crisis had been "a horror show" but accepts that the IAAF should have done more to stop doping.
"The best way to protect clean athletes is to be unflinching in our commitment to them, and not just in words," added Coe.
"We have to create structures that are always in their corner and here none of us come out very well - including my federation.
"The architecture of anti-doping has failed them. Were the walls too high in many of our organisations to properly investigate abuses? Almost certainly 'yes' has to be our uncomfortable answer."
IAAF president Lord Coe says athletics may not have a future if it does not eliminate doping.