Juices block drugs used to treat high blood pressure.

Fruit Juices Block Common Drugs

Grapefruit, Orange, Apple Juices Decrease Absorption of Many Often-Used Drugs


WebMD Health News
Reviewed by Louise Chang, MD
Aug. 19, 2008 -- Grapefruit, orange, and apple juices block drugs commonly used to treat infections, allergy, transplant rejection, cancer, and high blood pressure.

In 1991, David G. Bailey, PhD, and colleagues found that grapefruit juice increased blood concentrations of the blood pressure drug Plendil to possibly dangerous levels. Grapefruit juice, they later learned, slows down a key liver enzyme that clears Plendil -- and about 40 other drugs -- from the body.

Now Bailey reports that grapefruit, orange, and apple juices decrease the absorption of several important medications:

The allergy drug Allegra, available generically as fexofenadine
The antibiotics ciprofloxacin (Cipro, Proquin), levofloxacin (Levaquin), and itraconazole (Sporanox)
The beta-blocker blood pressure drugs atenolol (Tenormin), celiprolol, and talinolol
The transplant-rejection drug cyclosporine (Gengraf, Neoral)
The cancer chemotherapy etoposide (Toposar, Vepesid)
"This is just the tip of the iceberg. I'm sure we'll find more and more drugs that are affected this way," Bailey says in a news release.

Bailey revealed the new findings in a report to the 236th annual meeting of the American Chemical Society.

A substance in grapefruit juice called naringin seems to be the culprit. The compound apparently blocks OATP1A2, a transporter molecule in the gut, which carries some drugs from the small intestine into the blood. Orange juice contains hesperidin, a naringin-like substance. The culprit in apple juice remains unidentified.

"The concern is loss of benefit of medications essential for the treatment of serious medical conditions," Bailey says.

In their studies, Bailey and colleagues had healthy volunteers take fexofenadine with either a glass of grapefruit juice, a glass of water mixed with naringin, or pure water. Taking the drug with grapefruit juice or the naringin mixture halved the amount of drug that reached the bloodstream.

People should take their pills only with water, advises Bailey, a professor of clinical pharmacology at the University of Western Ontario, London, Canada. He suggests that people taking medications should check with their doctor or pharmacist before taking medications with fruit juices or whole fruits.
By Daniel J. DeNoon

Why opioid pain killers don't work.

People who have the common chronic pain condition fibromyalgia often report that they don't respond to the types of medication that relieve other people's pain.

New research from the University of Michigan Health System helps to explain why that might be: Patients with fibromyalgia were found to have reduced binding ability of a type of receptor in the brain that is the target of opioid painkiller drugs such as morphine.

The study included positron emission tomography (PET) scans of the brains of patients with fibromyalgia, and of an equal number of sex- and age-matched people without the often-debilitating condition. Results showed that the fibromyalgia patients had reduced mu-opioid receptor (MOR) availability within regions of the brain that normally process and dampen pain signals -- specifically, the nucleus accumbens, the anterior cingulate and the amygdala.

Fibromyalgia patients had reduced mu-opioid receptor (MOR) availability within regions of the brain that normally process and dampen pain signals – specifically, the nucleus accumbens, the anterior cingulate and the amygdala.

"The reduced availability of the receptor was associated with greater pain among people with fibromyalgia," says lead author Richard E. Harris, Ph.D., research investigator in the Division of Rheumatology at the U-M Medical School's Department of Internal Medicine and a researcher at the U-M Chronic Pain and Fatigue Research Center.

"These findings could explain why opioids are anecdotally thought to be ineffective in people with fibromyalgia," he notes. The findings appear in The Journal of Neuroscience. "The finding is significant because it has been difficult to determine the causes of pain in patients with fibromyalgia, to the point that acceptance of the condition by medical practitioners has been slow."

Opioid pain killers work by binding to opioid receptors in the brain and spinal cord. In addition to morphine, they include codeine, propoxyphene-containing medications such as Darvocet, hydrocodone-containing medications such as Vicodin, and oxycodone-containing medications such as Oxycontin.

The researchers theorize based on their findings that, with the lower availability of the MORs in three regions of the brains of people with fibromyalgia, such painkillers may not be able to bind as well to the receptors as they can in the brains of people without the condition.

Put more simply: When the painkillers cannot bind to the receptors, they cannot alleviate the patient's pain as effectively, Harris says. The reduced availability of the receptors could result from a reduced number of opioid receptors, enhanced release of endogenous opioids (opioids, such as endorphins, that are produced naturally by the body), or both, Harris says.

The research team also found a possible link with depression. The PET scans showed that the fibromyalgia patients with more depressive symptoms had reductions of MOR binding potential in the amygdala, a region of the brain thought to modulate mood and the emotional dimension of pain.

The study subjects were 17 women with fibromyalgia and 17 women without the condition.

The senior author of the paper was Jon-Kar Zubieta, M.D., Ph.D., the Phil F. Jenkins Research Professor of Depression in the U-M Department of Psychiatry and a member of U-M's Molecular and Behavioral Neuroscience Institute, Depression Center and Department of Radiology. Other authors were Daniel J. Clauw, M.D.; David J. Scott, Ph.D.; Samuel A. McLean, M.D., MPH; and Richard H. Gracely, Ph.D.

Reference: The Journal of Neuroscience, Sept. 12, 2007, 27(37):10000--10006.
ScienceDaily (Oct. 3, 2007)