"US: "No scientific evidence" for grapefruit medication claims"
Stewart pointed out an article that appeared in The Ledger that reveals that scientists with the Florida Department of Citrus have stated that no scientific evidence for such claims exists.
"We know of no validated evidence that co-administration of grapefruit juice with a
drug has caused a dangerous drug interaction resulting in ‘serious adverse effects' or
actual harm to a patient's health," Dan King, the department's director of scientific
research, said.
The study raised the total number of medications subject to harmful interactions
with grapefruit products to 43 oral drugs, more than double the total four years ago,
plus more than 40 drugs with minor interactions. The list includes cardiac and
cholesterol-lowering medications widely prescribed to middle-aged and older
people, the largest consumers of grapefruit products.
David Greenblatt, professor of pharmacology and experimental therapeutics at Tufts
University in Boston and a paid consultant for the Citrus Department, supported
King's statements.
Greenblatt criticized another table showing eight "case reports" of serious harm from
grapefruit-drug interactions.
"These case reports do not demonstrate cause and effect. They're invalid, anecdotal
evidence," he said.
The only scientifically valid proof of a harmful interaction would have to come from
human clinical trials, in which some participants receive grapefruit juice along with
a suspect medication, while another group receives a placebo and juice, he said.
Researchers would then test all participants for differences in physical responses.
In some cases, human clinical trials of some drugs listed in the Canadian journal
refute the authors' claims of a harmful grapefruit-drug interaction, Greenblatt said.
He cited his own clinical trial done with Watson Clinic and the universities of Florida
and South Florida measuring the effect of grapefruit juice and atorvastatin, a
cholesterol-lowering drug sold under the brand name Lipitor. The Citrus
Department financed the study, which was published last year in the British Journal
of Clinical Pharmacology.
The study found grapefruit juice showed "no meaningful enhancement" on
cholesterol levels and no evidence of liver or muscle damage.
Some clinical studies do show a harmful grapefruit-drug interaction, such as the
cardiac drug felodipine (brand name Plendil) and the cholesterol drug simvastatin
(Zocor), Greenblatt said. But many drugs reported in the Canadian journal as having a harmful interaction did not show that in clinical trials, including buspirone (Buspar and Vanspar) to treat anxiety and the cardiac drug erythromycin (several brand names, including E-mycin), he said.
"The tables he constructed are based on theory and conjecture," Greenblatt said.
"The authors are "basically constructing the worst-case scenario. That's not how we do business."