ATLANTA (AP) _ The pattern is becoming familiar.

Of the five Olympic athletes expelled so far for doping offenses, all are from the former Soviet Union and all tested positive for the controversial drug bromantan.

The latest case involved Russian sprinter Marina Trandenkova, the fifth-place finisher in the women's 100 meters.

She was disqualified Thursday by the International Olympic Committee. It was the first case involving a track and field athlete at the Atlanta Games.

Trandenkova was the fourth Russian athlete banned for taking bromantan, which was added to the list of prohibited substances about six weeks before the Olympics started. The other Russians were two swimmers and a Greco-Roman wrestler.

A cyclist from the former Soviet republic of Lithuania also was disqualified for bromantan, and her team doctor and coach were expelled for supplying the drug.

The five positive doping cases match the total at the Barcelona Olympics four years ago. The Atlanta competition has not concluded, and a backlog of tests still must be analyzed.

The Russian Olympic committee has appealed two of the disqualifications, and the Court of Arbitration for Sport is hearing the appeals. Court general secretary Jean-Philipe Rochat said the panel would meet again today, but a final ruling could be delayed until after the games end.

The Russian Olympic committee denies that bromantan is a stimulant and argues that it is not cited by name on the IOC's list of banned substances.

Prince Alexandre de Merode, the IOC medical commission chairman, said bromantan is a proven amphetamine-like stimulant covered under the heading ``related substances'' on the banned list.

IOC spokeswoman Michele Verdier said bromantan was declared illegal on June 5.

Russian Olympic officials have said their athletes are being singled out for political reasons.

``I believe that someone is not happy about Russian victories, and that this is all about exerting psychological pressure on our athletes,'' Russian Olympic committee president Vitaly Smirnov told the Itar-Tass news agency.

``We are now witnessing yet another `doping war' that has a distinctly anti-Russian flavor,'' the newspaper Komsomolskaya Pravda commented.

The IOC also said Thursday that Irish 5,000-meter runner Marie McMahon was reprimanded after testing positive for a stimulant contained in Robitussin, a cold and cough medicine readily available without a prescription.

``The athlete admitted that she took the drug without telling anyone,'' IOC spokeswoman Michele Verdier said.

She said levels of the banned substance were found ``in her body in a higher concentration than allowed.''

The drug, whose generic name is phenylpropanolamine, is on both the list of banned substances and the list of authorized substances because there are two kinds of it, Verdier said.

McMahon received conflicting information from the Irish national Olympic committee and the Irish track federation, Verdier said.

``The IOC reprimanded the athlete for not consulting the team doctor and strongly told the delegation of Ireland that their athletes are not very well cared for, and that causes some problems,'' she said.

McMahon, the NCAA indoor 5,000-meter champion from Providence College, failed to qualify for the 5,000 final, finishing 14th of 15 runners in her heat.

``It was a silly thing to do, but it was a terrible mistake and I'm just so grateful for all the support I received,'' she said in a statement released by team officials.

McMahon was the second athlete to receive a reprimand for a drug-related offense. Cuban judo competitor Estela Rodriguez Villaneva was warned for taking a banned diuretic.