* Two athletes test positive for drugs at Sochi Olympics
* German and Italian thrown out of Olympics
* Only one athlete caught at 2010 Vancouver Games (Updates with details, quotes)
By Karolos Grohmann
SOCHI, Russia, Feb 21 (Reuters) - Germany's two-times Olympic cross-country skiing champion Evi Sachenbacher-Stehle and Italian police officer and four-man bobsledder William Frullani were thrown out of the Olympics on Friday after testing positive for drugs.
Sachenbacher-Stehle, who, after switching sports two years ago, was competing in the biathlon in Sochi but did not win a medal. She tested positive for the stimulant methylhexanamin with the second "B" sample tested on Friday.
"The (German Olympic Committee) DOSB stands for a doping-free sport and a zero tolerance," said German team chief Michael Vesper. "We only want clean performances. Every doping case is initially a disappointment but also proof that the system works."
Germany's anti-doping agency had warned athletes many times that some supplements could contain that substance, Vesper said.
Sachenbacher-Stehle, provisionally banned for five days before the start of the Turin 2006 Olympics for high levels of haemoglobin in her blood, won gold in the team sprint at the 2010 Vancouver Olympics and in the 4x5km relay at the 2002 Salt Lake City Games.
The 33-year-old, who also has three Olympic cross country silvers to her name, narrowly missed out on medals in Sochi, coming fourth in both the 12.5km mass start and the mixed relay.
"This is the worst nightmare you could imagine," she told reporters. "I can't explain to myself at all how the doping test could be positive.
"At the moment I can only explicitly assure all those involved that I will do everything to clarify this issue beyond doubt."
She faces a standard two-year ban as a first-time offender.
Frullani, a police officer by profession, was dropped from the team due to compete on Sunday after testing positive for the substance dymetylpentylamine, and left the village.
The substances is registered as a specified substance in the World Anti-doping Agency code which means he could potentially have taken it inadvertently and could face a smaller sanction than the two years.
It can also be found in nasal decongestants.
Italian team officials said they had been given a green light by the International Olympic Committee to replace Frullani, a former decathlete who switched to bobsleigh in 2012, in their four-man team due to race on the last day of the Games.
"The Italian Olympic Committee (CONI) now needs to sort out the composition of the bobsleigh team which Frullani was part of, to make it back up to four," CONI said in a statement.
They have requested that the athlete be replaced by the reserve Samuele Romanini and clearance for this has been received from the IOC.
The two cases mean the Sochi Games have had more positive tests than the Vancouver 2010 Olympics, where only one athlete was caught for using banned substances.
The IOC said before the Olympics it was planning to carry out 2,453 tests during the Games, including 1,269 pre-competition controls, which is a record for a Winter Olympics.
It has also increased pre-Olympic testing in the months leading up to the event so as to stop cheats from getting to the Games.
All Olympic medallists are tested as well as several other finalists, while hundreds more targeted tests are conducted based on intelligence.
Samples taken at the Sochi Olympics will be stored for a decade and re-tested in line with the new World Anti-Doping Code that comes into effect on Jan. 1, 2015.
Germany, who are fifth in the medals table with eight golds, sent a total of 154 athletes to Sochi. Italy, who have yet to win gold in Sochi, sent 114 athletes. (Additional reporting by Julien Pretot and Annika Briedthardt in Rosa Khutor; editing by Mitch Phillips)