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Why can't I take certain medications with mineral or spring water?

Q) I'm taking weekly alendronate alongside prednisolone for polymyalgia rheumatica (PMR). I hope to go for a winter holiday in Europe. The alendronate leaflet states that they must only be taken with tap water. The water abroad isn't always drinkable, so why can’t I take them with mineral or spring water? My chemist doesn’t know either.
M Prior, Sleaford, Lincolnshire (Autumn 2007)

A) I think the problem here is the calcium content of some mineral waters. The calcium interferes with the absorption of the alendronate. Most European countries now have perfectly drinkable tap water in terms of safety. It may not taste like your tap water but it's an acceptable alternative. Of course, the calcium content of tap water does differ a lot from place to place (both abroad and in the UK) but I'd guess that even where the water is ‘hard’ (higher calcium content) the amount of calcium is insufficient to interfere with the alendronate.


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