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Biotech / Medical : VVUS: VIVUS INC. (NASDAQ) -- Ignore unavailable to you. Want to Upgrade?

To: VLAD who wrote (19176)	3/2/1999 1:17:00 AM
From: Zebra 365	Read Replies (2) \| Respond to of 23519

VLAD, this is a recycled post I published here about a year ago: <<How will grapefruit juice affect a man who uses Viagra? (Sildenafil)>> Many drugs are deactivated in the liver. In this case think of the liver as a factory in reverse (like a "chop shop" for stolen cars), it disassembles sildenafil molecules into another molecule (which still has some effect, 50%) and then disassembles that molecule into something that has no effect (that is then eliminated in the urine (13%) or feces (80%). In healthy young volunteers this process eliminates 50% of the drug in 4 hours (and 25% in the next four hours, and 12.5% in the next four hours) Theoretically after 12 hours you would still have 12.5% of the drug in your system, and it would be effectively gone after 24 hours (six half lives). Healthy elderly (>65) volunteers cleared sildenafil less than the younger ones, resulting in plasma levels 40% higher at the same dose. In someone drinking grapefruit juice or eating a grapefruit, this factory line could be as much as 90% shut down. This could increase the half-life of Viagra by ten-fold, i.e. a factory working at 10% capacity takes 10 times as long to produce as much. If this then extended the half-life by 10-fold it would become forty hours instead of four, then the dose you take on Tuesday is still mostly around when you take a dose on Wednesday and would have additive effect. (PFE recommends no more than one dose per 24 hour period.) As side effects increased with dosage in the reported studies (plasma levels) this would likely increase the side-effects (and desired effects) of the drug. Exactly to what extent I cannot say. As I mentioned, this grapefruit effect on this enzyme system, has only recently (March 1998) been discovered and is now being studied. Most drugs known to use this enzyme system are now having grapefruit warnings added to their label material. PFE warns about ketoconazole type drugs and other "inhibitors of these isoenzymes" with Viagra but did not mention grapefruit juice. They did try giving 100mg a day to someone at the same time that person was taking a normal dose of erythromycin. This resulted in sildenafil 182% higher levels. Erythromycin is nowhere near as powerful an inhibitor of this enzyme system as grapefruit juice. Tagamet (800mg) given with a single 50mg dose of Viagra, caused a 56% increase in plasma concentration of Viagra in healthy volunteers (age not given) Elderly people already have reduced activity of this system, couple that with an AM grapefruit, and that dose of Viagra, you see my point? My main point is that people often think of drug-drug interactions but often little attention is given to drug-food interactions. Yet, the grapefruit effect on certain drugs is one of the more important drug-food interactions yet discovered. I suspect PFE will add it to the label material soon. (I was wrong) With all the hype that Viagra gets, it would be an excellent chance to increase general awareness (among both physicians and patients) of this newly discovered grapefruit interaction. (Now I'm probably kicked off the mailing list for the Texas Ruby Red Grapefruit people. I love those, have some in the fridge right now and send them for Xmas gifts, see why I have to use a pseudonym!) Zebra P.S. I do not think this applies to all citrus fruit, only grapefruit as far as has been reported.