The eight were among 26 athletes facing two-year bans after being accused by the National Anti-Doping Organisation (NADO) in December of evading doping controls or failing to be available for them.
CONI said in a statement that decisions on the remaining 18 had still to be taken.
The case followed a police investigation in the northern Italian region of Trentino Alto Adige.
American-born Howe won the European long jump title in 2006 and a world championship silver medal a year later.
Donato, 39, was European triple jump champion in 2012 and finished third at the London Olympics the same year.
European marathon champion Daniele Meucci, Daniele Greco, Ruggero Pertile, Silvia Salis, Anna Incerti and Andrea Lalli were also acquitted, CONI said.
Italy's athletics federation has defended the 26, saying the affair was a question of inefficient procedures rather than illicit substances.
It has blamed communication failings due to faulty fax machines, problems with email passwords and digital apps that did not work properly.
Athletics was plunged into crisis after a report by the independent commission of the World Anti-Doping Agency (WADA) in November detailed systematic, state-sponsored doping and related corruption in Russia, which has been banned from the sport.
On Monday, the Russian Athletics Federation said four of its track-and-field competitors have tested positive for the banned drug meldonium, a disclosure which could further damage Moscow's efforts to overturn the ban in time for the Rio Olympics in August.
(Writing by Brian Homewood; Editing by Tony Jimenez)
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