Levitra, or vardenafil, is one of several oral medications used to treat erectile dysfunction, or ED. Levitra belongs to a class of agents called phosphodiesterase-5, or PDE5, inhibitors. Like all drugs in this class, Levitra improves blood flow to the penis, thereby helping maintain an erection to permit sexual intercourse. Levitra was approved for marketing by the U.S. Food and Drug Administration in August 2003 and soon after joined other drugs on a growing list of medications that interact with grapefruit.
Mechanism of Action
PDE5 is an enzyme found in several tissues, including your blood vessels, lungs, intestines and eyes. It is found in particularly high concentrations in the smooth muscle cells lining the blood vessels of your penis. PDE5 breaks down a molecule called cGMP, thereby reducing your cells’ ability to produce nitric oxide. Nitric oxide promotes blood vessel dilation, which enhances blood flow to the penis and improves erectile function. By blocking PDE5, Levitra increases cGMP levels, boosts nitric oxide production and strengthens erections. Notably, Levitra blocks PDE5 throughout your body.
How Levitra is Metabolized
Like many drugs, Levitra is partially metabolized by a specific enzyme, called CYP3A4, in the lining of your intestine. This “first pass” metabolism reduces the amount of Levitra absorbed into your bloodstream. Drugs, however, are formulated to compensate for first pass metabolism, so they are administered at dosages that are effective but not too high. A 2004 review in “American Journal of Cardiovascular Drugs” reported that grapefruit and grapefruit juice interfere with the action of CYP3A4, thus reducing Levitra’s first pass metabolism and permitting more of the medication to pass into your bloodstream.
Levitra Side Effects
If you consume grapefruit in conjunction with Levitra, the medication’s effects throughout your body will be magnified, and its side effects – dizziness, flushing, headache and nausea – could be intensified. Heightened blockade of PDE5 can lead to “over-dilation” of your blood vessels, resulting in a significant and potentially dangerous drop in your blood pressure. This grapefruit-Levitra interaction could result in fainting, and if you have coronary artery disease your risk for heart attack might also be increased.
Considerations and Precautions
Levitra, like all PDE5 inhibitors, interacts with grapefruit in a manner that accentuates the medication’s effects in your body. This increases your risk for potentially serious side effects. According to scientists at London Health Sciences Centre in Ontario, Canada, in the 2004 "American Journal of Cardiovascular Drugs," grapefruit can interfere with Levitra’s metabolism for at least 24 hours. Therefore, you should avoid consuming grapefruit or grapefruit juice for more than a day before using Levitra. If you use grapefruit products on a regular basis, ask your doctor if there are alternatives to Levitra for treating erectile dysfunction.