By Alison McCook

NEW YORK (Reuters Health) - People who take an extended-release form of the blood pressure drug felodipine with a glass of red wine on an empty stomach may run into problems, according to findings from a new small study.

Canadian researchers discovered that when eight healthy people took extended-release felodipine (Plendil) -- a form of the drug intended to release an entire day's dose slowly and constantly -- on an empty stomach and with a glass of red wine, only traces of the drug filtered into their blood.

However, four hours later, when the participants ate lunch, blood levels of felodipine spiked, filling people's bodies with a huge dose of the drug.

"You go from no effect to toxicity," study author Dr. David G. Bailey, of London Health Sciences Center in Ontario, told Reuters Health.

"It was like taking an overdose," he said.

Felodipine helps alleviate high blood pressure by opening up blood vessels. In healthy people like those in this study, a burst of the drug into the bloodstream is unlikely to be harmful. But a similar spike in a person with high blood pressure could be dangerous, Bailey explained.

For these people, who often have other cardiovascular conditions as well, too large a drop in blood pressure can cause chest pain or possibly a heart attack, Bailey said. In addition, a sharp decline in blood pressure can result in fainting, he added.

Based on these findings, which appear in the June issue of the journal Clinical Pharmacology & Therapeutics, Bailey recommended that people taking the extended-release form of felodipine not do so on an empty stomach, with a glass of red wine.

He added that extended-release forms of other drugs might also interact badly with red wine, but more research is needed to answer that question.

During the study, Bailey and his colleagues asked eight people to take extended-release felodipine on an empty stomach with either a glass of red wine or water, and measured levels of the drug in participants' blood for eight hours. Participants ate a meal four hours after taking the drug.

The researchers found that people who took the drug with red wine showed much lower early levels of the drug in their blood, relative to when they downed the pill with a glass of water. After lunch, however, red wine drinkers saw a spike in levels of felodipine that was much higher than when they drank water.

The person with the highest peak blood levels of felodipine also experienced a rapid heart rate, palpitations and flushing, the authors report.

Bailey said that the extended-release form of felodipine, when taken on an empty stomach with red wine, is likely undergoing a process of "dose dumping."

He explained that drugs are absorbed into the bloodstream when they pass into the intestine. However, when taken with red wine without food, the extended-release form of felodipine may be getting stuck in the stomach, and not passing into the intestine until a few hours later, when it dumps a large dose of the drug into the blood.

Bailey said he and his colleagues don't know whether red wine consumed with a meal might cause a problem if combined with the drug.

He noted that patients are also cautioned against taking some drugs with grapefruit juice, for compounds in the juice inactivate the enzymes that normally break down drugs, causing patients to get a higher-than-expected dose.

SOURCE: Clinical Pharmacology & Therapeutics 2003;73:529-537.