ANTIBIOTICS CAUSE FALSE POSITIVES ON HEROIN TEST

NEW YORK (Reuters Health) - Athletes and hopeful job applicants often hinge
their careers on a clean drug test, but the use of certain antibiotics may
cause an unsuspecting person to test positive for heroin even though they've
never touched the drug, according to study findings released Tuesday.

Researchers led by Dr. Lindsey R. Baden of Harvard Medical School (news -
web sites) in Boston, Massachusetts, investigated this problem after they
came across a patient in their practice who tested positive for opiates, and
who was also taking an antibiotic called levofloxacin. The patient was
nearly kicked out from a drug treatment center because of the result, which
later proved to be false.

Opiates are a class of drugs that include the illegal drug heroin, and
several other controlled drugs such as methadone, morphine, Demerol and
codeine.

In their study, Baden and colleagues tested 13 different types of
antibiotics, including levofloxacin and Cipro, all belonging to a class of
chemicals called quinolones, to see what effect they would have on
commercial opiate tests.

The researchers diluted the antibiotics to concentrations that would be
expected to occur in urine and then tested the antibiotic samples using five
different commercial tests to see if they would cause a positive result for
opiates.

Two antibiotics, levofloxacin and ofloxacin, caused a strong positive result
on four of the five tests.

Most of the other antibiotics also caused a positive result on at least two
or three of the five tests. For example, Cipro, the drug given to thousands
of people to fight possible anthrax exposure, resulted in a positive test in
one out of the five tests.

To confirm these results in people, they had six people take a standard dose
of one of the two antibiotics and collected their urine samples every 6
hours for the next 48 hours.

On one of the five tests, all three patients taking levofloxacin tested
falsely positive within 2 hours and up to 22 hours after taking the drug.
The results were similar in patients taking ofloxacin, the investigators
report in the December 26th issue of The Journal of the American Medical
Association (news - web sites).

Baden told Reuters Health that he suspects that the false positives result
from the similar three-dimensional structures of opiates and the
antibiotics. He also pointed out that other types of chemicals could cause a
similar reaction.

According to Baden, it is possible that people have suffered consequences of
a false positive test, because ``a positive drug test is often assumed true,
while the protestations of the person being tested are looked at as
self-serving.''

Baden recommends that anyone who tests falsely positive for opiates ask to
have drug testing performed to confirm the result.

SOURCE: The Journal of the American Medical Association 2001;286:3115-3119