Interesting medical question

A customer called in to find out whether she had hard water where she lives. It turns out she's taking medication and if she's got hard water, it's been suggested that she take it with distilled water.

I told her she gets "medium" (by industry standards) water, and asked her what medication it was. It turns out to be the generic form of Fosamax, a treatment for osteoporosis.

I gave her the numbers for the hardness in her area, and suggested she run it past her pharmacist to verify this was soft enough. She said the advice was even news to her pharmacist.

So I went Googling.

Looking under "Fosamax", "water", and "hardness", I found a document that gave me the scoop. The link has since moved, so I used the cached version.

Medication Absorption with Hard Water Reminder: If your community has hard water, you may want to consider advising your patients to use distilled water when taking specific medications. The absorption of some drugs is affected by the hardness of water. For instance, the patient insert for Fosamax® (alendronate sodium) states that “because of high mineral content, ‘hard water’ may decrease absorption of FOSAMAX. If your normal drinking water is classified as ‘hard water,’ you should consider taking this medication with distilled water (i.e. not mineral water).” The pharmacist who reminded us of this issue contacted Merck Frosst and was advised that, since only a small amount of Fosamax is absorbed by the body, any further decrease in absorption could have a significant impact on the efficacy of the drug. Environment Canada has defined soft and hard water as:

• very soft water 0 to 60 ppm. calcium carbonate
• less soft water 61 to 120 ppm. calcium carbonate
• hard water 121 to 180 ppm. calcium carbonate
• very hard water > 180 ppm. calcium carbonate

This does not mean all the calcium in your water has to be carbonate to count as hardness – it's typical to calculate hardness as if all the calcium found were the carbonate salt.

It occurs to me, if the serum concentration of the drug is that sensitive to hardness, you might want to take the pills with distilled water anyway. And don't take any Tums or any other calcium-basd antacids within about an hour of taking the pills, either.

And of course, no milk or cheese, or other calcium-rich foods during that time, as well.

What we need here is some real numbers on how much of an effect dietary calcium has on the serum concentration of the drug. It might be this is an effect that is what I call "significant but not useful". It shows up in the lab under analysis, but is otherwise swamped in the normal variation that appears in daily life.

I'm going to speculate that it won't make any real difference. However, it might make people feel better if they make these minor changes in their lives.