Grapefruit Juice and Finasteride/Dutasteride Absorption

Dear Doctor:

This is in response to a post that I saw regarding grapefuit juice and Propecia/Avodart absorption. Grapefruit juice inhibits the Cytochrome P-450 intestinal enzyme CYP3A4. It does not affect the hepatic enzyme apparently. Dutasteride is metabolized extensively by this enzyme. The serum level of any CYP3A4 substrate, such as Dutasteride, will be elevated in the presence of GF juice. Additionally, grapefruit juice takes quite some time to leave the body, so it’s effect is cumulative. If someone drinks 1 glass a day for 5 days, CYP3A4 will be significantly reduced. Additionally, one 8-oz glass of grapefruit juice inhibits CYP3A4 as much as 2-3 double strength glasses, so you don’t need much. Ketoconazole is also a very potent CYP3A4 inhibitor. Now, I am sure most readers would not be against elevated serum levels of Dutasteride/Finasteride as the effects of dutasteride (at least) is dose-dependent. However, many other drugs such as antivirals, statin drugs, antihypertensives, antiseizure medications, and many allergy medications are also CYp3A4 substrates. Elevated serum levels of these drugs can prove deadly, so as a general rule, patients should check with their doctors regarding any drug/food interaction.

Just my 2 1/4 cents. Thanks!

Thanks for the information. There are some medications that do not do well with grapefruit juices, but here some other links to explore about this —

• Grapefruit Juice And Medication Can Be A Dangerous Mix
• Grapefruit juice squeezes more out of some medications
• Drug – Grapefruit Interactions (Review)

And there’s more links in a previous blog post here.