Dietary Supplements and the Ophthalmologist

Stephen G. Schwartz, MD; Pamela S. Chavis, MD


Compr Ophthalmol Update. 2005;6(3):153-159. 

In This Article

Effects on Medications

Many dietary supplements impact the cytochrome P450 oxidase system, thus affecting pharmaceuticals that are metabolized by these pathways. The cytochrome P450 3A4 (CYP3A4) isoform metabolizes many common medications, including calcium channel blockers and 3-hydroxy, 3-methylglutaryl coenzyme A reductase inhibitors (statins). Many agents demonstrate in vitro inhibition of the CYP3A4 isoform, resulting in increased serum levels of these medications, including chamomile; echinacea; garlic; goldenseal (Hydrastis canadensis), used as an antibiotic; and licorice.[37,38]

Conversely, the antidepressant, St. John's wort (Hyperium perforatum), induces the CYP3A4 isoform and therefore decreases serum concentrations of these compounds. St. John's wort also induces the CYP1A2 and CYP2C9 isoforms as well as the transport protein, P-glycoprotein.[3,39] This reduces the serum concentrations of cardiac glycosides, oral contraceptive agents, warfarin, HIV protease inhibitors (such as saquinavir, Invirase®, Hoffman-LaRoche, Inc., Nutley, NJ), and HIV non-nucleoside reverse transcriptase inhibitors (such as efavirenz, Sustiva®, DuPont, Wilmington, DE).

The effects of various dietary supplements on the cytochrome P450 system are summarized in Table 3 . Certain supplements may interact with medications through mechanisms other than hepatic metabolism. Licorice may potentiate the cardiac glycosides, possibly through effects on blood electrolyte levels.[40] This is important to the ophthalmologist because overdoses of cardiac glycosides may cause direct retinal toxicity, typically manifesting as xanthopsia.[41]

Various agents (such as echinacea, ginseng, and licorice) have known or proposed stimulatory effects on the immune system, and may inhibit corticosteroids and other immunosuppressive agents.[42]


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