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James McNabb, M.D., C.N.

Drugs and Grapefruit

I came across an article lately that has really got me thinking, much like reading an exciting detective story. Several years ago (prior to knowing much about nutrition), I was taking antihistamines for urticaria, a delayed hypersensitivity allergic disease characterized by whelps on my skin and difficulty swallowing. There were seasons when I was taking as many as 5 antihistamine pills a day to avoid these unpleasant symptoms. Almost as unpleasant were the side effects of drowsiness and lethargy. I was therefore delighted when the non-sedating antihistamines Seldane and Hismanol were released to the market. 

Hismanol

It was during this period of taking Hismanol when I had what I thought was a fainting episode at the office. I was taken to the ER where they did an EKG. I even had another fainting episode there on a stretcher, flat on my back. This is not how normal fainting episodes take place. You are usually standing. Lying down relieves them. So, something else was clearly at work here. The EKG there, as well as a complete cardiac workup over the next few days revealed nothing. The cardiologists shook their heads and stated that they did not know what happened. What a mystery!

Somewhat later I learn that Hismanol is taken off the market due to cardiac complications, meaning cardiac deaths have occurred due to irregular heartbeat. Was my previous fainting episode due to Hismanol? I had taken it for some time. In fact, Hismanol was on the market for several years before being removed. It seems there is another piece of the puzzle that is missing.

Grapefruit

I came across an interesting article on the Internet while searching about Hismanol concerning the toxicity of drugs and eating grapefruit. It seems that eating grapefruit and taking drugs can be hazardous to your health. What is this all about? Well, it seems that grapefruit contains substances that block our cytochrome P-450 system. This system is active in our liver and GI tract to render toxins harmless. Since most drugs have been developed in the last quarter of this century, our body considers them as toxins and uses the cytochrome P-450 system enzymes to destroy them. Thus when you eat grapefruit and take drugs at the same time, you can run the risk of having dangerously high levels of the drugs, enough to cause serious problems. The list of medications that can be affected by eating grapefruit is rather large, including calcium channel blockers (Plendil, Procardia XL, Calan), antihistamines (Seldane and Hismanol), benzodiazepines (Xanax and Halcion) and statins (Mevacor, Zocor, and Lipitor).

Recommendation

Eating a single grapefruit is not likely to be a problem. However, in my case, I am often given a dozen grapefruit either for Christmas or in February for my birthday. I will usually eat a grapefruit or two a day for a week or more. This could more than account for all that had happened to me. It would also explain why the manufacturer of Hismanol did not know about possibly fatal cardiac arrhythmias for several years after its introduction.

The bottom line here is to be careful eating multiple grapefruit if you are taking medications. It may result in an over dosage of the medication.

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